tag:blogger.com,1999:blog-9591491885112665122024-03-06T04:44:30.259+11:00syymmetriesBluejayhttp://www.blogger.com/profile/06935684943024856641noreply@blogger.comBlogger51125tag:blogger.com,1999:blog-959149188511266512.post-65667804019508950332017-06-25T15:11:00.000+10:002017-07-09T10:30:33.416+10:00Naturalness: A Pragmatist's Guide<div style="text-align: center;">
<b>1. The long read</b></div>
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I've been meaning to write a more comprehensive reflection on naturalness here for a while now, ever since penning a summary in the introduction to my <a href="http://inspirehep.net/record/1503457">PhD Thesis</a> (now conferred) and submitting <a href="https://arxiv.org/abs/1607.07446">a paper</a> on the topic (now published). During my graduate studies, I spent a lot of time earnestly trying to understand the assumptions on which naturalness was predicated, and how those assumptions might be written down hierarchically as a quasi-nested set, in order to appreciate what a "strong" or "conservative" stance on naturalness would entail. I did not find this to be an easy task. Instead, I found the literature to be plagued with oversimplifications, hand-waving, a lack of distinction between physical and unphysical quantities, definitions which are imprecise and inconsistent, and a great many unmentioned and/or unconsidered assumptions. Eventually I began to piece together my own understanding, and it became clear that the subject is more nuanced than many seem to appreciate, deserving a more careful treatment than what is typical.<br />
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I offer this post as an attempt at a comprehensive summary of my current understanding, in the hopes of getting people to at least step back and question what they thought they knew about naturalness. Throughout I will challenge conventional wisdoms. I am not intentionally trying to be provocative, just that I don't believe some of the things that are often said with regard to naturalness actually pass muster, and I will try to make it clear just why. The views are my own. The layperson will be able to follow for a while, however I will not make special effort to keep the latter prose below a graduate level. It is a long read, but it needs to be.<br />
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<b>2. What do we mean by naturalness? </b></div>
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When we talk about naturalness we are talking about the required values of input parameters which enter a theory in order to explain observations (i.e. to basically reproduce the standard model at low energy). The descriptor "natural" is commonly used in two distinct senses in the literature.<br />
<ol>
<li>A theory may be called natural if the required dimensionless input parameters are of $\mathcal{O}(1)$. (If there are input parameters with mass dimension, then this criterion requires all those mass scales to be similar).</li>
<li>A theory may be called natural if the required input parameters do not need to be very precisely specified.</li>
</ol>
These senses are quite different; a theory can satisfy the first condition without satisfying the second, and vice versa. It is the second sense, and naturalness of the Higgs mass in particular, which the remainder of this post is dedicated to, and henceforth what we take as the qualitative definition of what it means to be natural.<br />
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<b>3. What do we mean by "very precisely specified"?</b></div>
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Actually there is a not-so-subtle yet under-appreciated point to be made here, because there is a local and a global sense in which the parameters could be described as precisely specified. Both are used in the literature.<br />
<ol>
<li>In the local sense, a theory is natural if small perturbations around the required input parameters does not wildly change the observables. </li>
<li>In the global sense, a theory is natural if the observables are not "improbable" when considered over the range of possible values the input parameters could have taken on.</li>
</ol>
The first "local naturalness" sense is usually what is referred to as "fine-tuning" (but not always), and it is easy to understand why people use measures involving partial derivatives to quantify such naturalness (we will cover this later on). The second "global naturalness" sense is essentially what is explored when people perform parameter scans.<br />
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It is tempting to think of the first sense as a weaker requirement than the second—I do tend to categorise it loosely as such—since it is easy to imagine a theory where a small but finite "island" of parameter space reproduces low scale physics like observed; this would be a locally natural theory that is not globally natural. But it seems to me also possible at least in principle to have a globally natural theory that is not locally natural (think chaotic systems). So I do think these are in fact technically distinct senses and this should be acknowledged. I will use the terms "locally natural" and "globally natural" to refer to these two qualitative definitions henceforth where appropriate.<br />
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<b>4. Why should a theory be natural, anyway? </b></div>
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I think it's fair to say that the primary goal of theoretical particle physics is to discover the higher scale theory (and intermediate theories) from which the standard model (plus gravity) derives. The secret hope is that it uniquely predicts the standard model at low energy, i.e. that it is "perfectly" natural by the above definitions (it may even have inputs of $\mathcal{O}(1)$, or none at all). Failing that, the next secret hope is that it (loosely) generically predicts something <i>like</i> the standard model, i.e. that it is in some sense globally natural. The idea, I guess, is that the standard model should not be an accident but instead the inevitable outcome of some unified mathematical description – if only we could figure it out.<br />
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Many physicists would like, or subjectively feel like, this should be the case. It would be a somehow "neat" outcome. However, from a logical point of view, there is no guarantee that nature is actually like this. It is absolutely possible that nature is ultimately described by a set of mathematical rules with some input parameters which just "are what they are," and which may even be unnatural according to the above definitions.<br />
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<b>5. What people do</b></div>
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Nevertheless one is certainly free to make the <i>assumption</i> that the high scale physics is natural, optionally acknowledging the logical possibility that it is not, and use that assumption as a sort of guiding principle to constrain theory space. That is what people do.<br />
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<b>6. What people actually do</b></div>
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What people actually do (at least in hep-ph) is use the assumption of naturalness to constrain theories which are defined at a higher scale than the standard model, but not at so high a scale as to be considered <i>the</i> high scale theory. That is, if you consider the standard model as the end of a chain of effective theories all the way up to the highest scale, people are checking for naturalness halfway up the chain.<br />
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Why is this useful? There seems to be an implicit assumption here. The assumption is that naturalness of the theories halfway up the chain implies something about the naturalness of the theories above. But this needn't be the case. Even if it were the case it might be only at a very high scale that the theories begin to look natural. It is a logical possibility that, when viewed one by one, the chain links actually realised in nature might appear as any combination of "natural" and "unnatural" as you work your way up. A natural effective theory can be embedded in an unnatural theory, and an unnatural effective theory can be embedded in a natural one. Indeed, the latter idea can be used as a get-out-of-jail-free card; it's essentially the trick exploited by multiverse proponents, where an unnatural observable theory is made to be natural by embedding it in a large enough ensemble of theories, then appealing to anthropics. We could turn a natural theory into an unnatural one using the same trick.<br />
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The point here is that we should acknowledge when we are testing naturalness some way up the chain and that this does not <i>necessarily </i>imply anything about what's above. Still, this does not preclude the possibility—and this is what theorists hope—that it may be the successful algorithmic way to climb the theory chain all the way to its natural end. It might be true in some sense that natural theories mostly beget natural theories.</div>
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<b>7. Quantum corrections</b></div>
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Since the definitions of naturalness above involve observables and input parameters, we need to go into some technical detail to understand how parameters behave in quantum field theories. In particular, they are <i>not</i> constants. For instance, what is called the fine-structure constant $\alpha\approx 1/137$ changes value with energy scale, and even its value at fixed scale depends on the renormalisation scheme (more on this later) and loop level which you are working in. In other words, in quantum field theories, your parameters are "corrected" by quantum effects.<br />
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The nature of these quantum corrections is important for understanding exactly what kind of naturalness problem we're talking about. There are three general cases I want to highlight which represent different levels at which a theorist might worry.<br />
<ol>
<li>It might be that a parameter needs to be very precisely specified in a global sense, but nevertheless once it is specified it is stable under quantum corrections, because the corrections are proportional to that parameter. </li>
</ol>
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Indeed, if one were to set that parameter to zero, then the corrections would also be zero. This is usually indicative of an additional symmetry being introduced in that limit, and the parameter is called "technically natural" in the literature, a terminology introduced by 't Hooft. An example is the Yukawa couplings in the standard model. You might puzzle about <i>why</i> their values are the way they are (in the global sense), but nevertheless once they are set there is no local naturalness problem, due to the chiral symmetry reinstated when the Yukawas are set to zero. This is why you don't hear about a naturalness problem for the electron mass – there is no local naturalness problem, but rather a sort of global naturalness problem to be solved in explaining the Yukawa structure. The same is actually true of neutrino masses, although the global naturalness problem is considered somehow worse because the required Yukawa couplings are so much smaller than for the other fermions, suggesting that there might be another explanation.</div>
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<ol start="2">
<li>It might be that a parameter needs to be very precisely specified in a global sense, but nevertheless once it is specified it is stable under quantum corrections, because the corrections are sufficiently smaller than the parameter. </li>
</ol>
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</ul>
This is distinct from the previous case in that setting the parameter to zero does not reintroduce a symmetry. You couldn't call such a parameter technically natural, but you could still say that it is locally natural in the $\log$ of the parameter. An example is the QCD $\bar{\theta}$ parameter in the standard model. The $\bar{\theta}$ parameter has a global naturalness problem because a priori one expects this parameter could take any value up to $\mathcal{O}(1)$, however experiments have ascertained that its value is $\lesssim 10^{-10}$. If $\bar{\theta}$ is set to zero by hand at a high scale, quantum corrections reintroduce it, but only at the level $\sim 10^{-17}$. So there is a global naturalness problem to be solved (the "strong CP problem"), but once you have solved this you are done. People consider this case as more of a problem than the previous case, since there is no "increased symmetry" explanation that can be appealed to. Indeed, the way the $\bar{\theta}$ problem is usually solved is to introduce the appropriate symmetry by extending the standard model.<br />
<ol start="3">
<li>It might be that a parameter needs to be very precisely specified in a global <i>and</i> local sense, since that parameter needs to cancel off comparatively large quantum corrections to many significant figures in order to realise the low scale observations. </li>
</ol>
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This is considered as a much greater problem, since it appears to be just an unexplained and very precise conspiracy between a boundary condition and the quantum corrections. This is exactly the sort of conspiracy that is needed in certain quantum field theories with light scalars (like the Higgs) <i>which interact sufficiently strongly with heavy new physics</i>. That italicised text is often left out of the usual story, but it is important, as I will explain...<br />
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<b>8. The usual Higgs story</b><br />
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In the standard model the major naturalness worry is the Higgs mass-squared term $\mu^2 = -m_h^2/2 \approx -(88\text{ GeV})^2$. The usual introduction-slide story that is told is the following.<br />
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<i>One-loop Feynman diagrams introduce a "quadratically divergent" quantum correction to this term, $$\delta\mu^2 \sim \frac{1}{(4\pi)^2} y_t^2 \Lambda^2,$$ which depends on the "cutoff scale" $\Lambda$. If $\Lambda$ is very large then this quantum correction needs to be cancelled away very precisely in order to realise the observed Higgs mass.</i><br />
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Ostensibly this sounds like a naturalness problem of the third kind as written just above. But we should ask: what does $\Lambda$ represent and what exactly is cancelling it away?<br />
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<b>9. Input parameters in quantum field theories</b></div>
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To be true to the definition of naturalness we are working with, what we would actually like to do is see how the observables depend on the input parameters of the theory. So we can try to do just that; first we might think of taking the inputs as the parameters which enter the standard model Lagrangian, but we need to be careful, since quantum field theories are not that simple...</div>
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The parameters (and the normalisation of the fields themselves) which enter the Lagrangian of any quantum field theory are called "bare" quantities. If you try to calculate observables using these bare quantities you end up with a whole lot of infinities. Understanding and taming these infinities was an important problem of early quantum field theory. The key insight turned out to be the following: the bare quantities are not measurable. What is measured are the physical observables themselves, e.g. scattering cross-sections or decay rates, which are manifestly free from infinities. In order to proceed, from a calculational perspective, physicists learned to employ "regularisation" procedures to capture the divergences arising in the bare quantity calculations. Calculation results can then be made consistent with the finite physical observables by appending divergent counterterms to the bare quantities, which cancel with the divergences arising in the calculations. I think it is fair to say the modern interpretation is that the cancellation between divergences is just an unphysical intermediate artifact of the calculation procedure. Once the Lagrangian parameters are regularised (under some scheme) and rewritten in terms of physical observables, they are said to be "renormalised". These parameters are measurable.<br />
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<b>10. The cutoff scale in the standard model</b></div>
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The quadratic divergence $\propto y_t^2 \Lambda^2$ in the standard model is due to a "cutoff regulator" which captures the divergent quantum correction to $\mu^2$. What it must be cancelled against is the bare $\mu_0^2$ contribution, in order to realise the renormalised parameter $\mu^2(m_t)\simeq -m_h^2/2$. What to make of this "unnatural" cancellation? In my opinion there is only one consistent interpretation: it is just the regularisation and renormalisation procedure. The cancellation has no physical significance, since the cutoff regulator scale $\Lambda$ has no physical significance, it is just the arbitrary scale at which we choose to renormalise, essentially just being used as a dummy variable or dictionary to convert between observables and renormalised Lagrangian parameters. Indeed, the very procedure itself mathematically demands that any observable you calculate does not depend on which $\Lambda$ you choose.<br />
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<b>11. The standard model is natural</b></div>
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Again, to be true to the definition of naturalness we are working with, we want to see how the observables relate to the inputs. So what is the input parameter of interest? It can only be the renormalised parameter $\mu^2(\Lambda_h)$, defined at some high scale $\Lambda_h$ (where boundary conditions are specified), and not the bare parameter $\mu_0^2$, since after all I cannot measure $\mu_0^2$, and the regularisation procedure anyway forces me to choose a counterterm to realise the observed Higgs mass.<br />
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Next we must ask how the low scale parameter, $\mu^2(m_t)$, depends on the high scale input $\mu^2(\Lambda_h)$. An interesting implication (interesting enough for some Nobel Prizes, anyway) of the regularisation and renormalisation procedure is that the quantum parameters depend on energy scale according to the "renormalisation group equations". The renormalisation group equation for the Higgs mass-squared parameter in the standard model is $$\frac{d \mu^2}{d \log\Lambda_R} \approx \frac{6 y_t^2}{(4\pi)^2} \mu^2 ,$$ where $\Lambda_R$ is the renormalisation scale and the dependence of each parameter on $\Lambda_R$ is implied. If we take $y_t$ as a constant we can easily solve this to write $$\mu^2(m_t) = \mu^2(\Lambda_h) \left(\frac{m_t}{\Lambda_h}\right)^{\frac{6 y_t^2}{(4\pi)^2}}.$$ Even if we take $\Lambda_h\sim 10^{18}~\text{GeV}$ and $y_t\sim 1$, we have $\mu^2(m_t)\sim \mu^2(\Lambda_h)/4$. We see that the input parameter $\mu^2(\Lambda_h)$ has not at all needed to be precisely specified (in the local sense) to realise the observed Higgs mass (and in actuality the news is much better than a factor of 4, it is $\approx 1$, since the renormalised $y_t^2$ parameter shrinks with scale quite quickly).<br />
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What I am arguing here is that, when we only consider the parameters which have a physical significance, we can only conclude that the standard model is natural (in the local sense), since it is stable for small perturbations around the renormalised input parameter $\mu^2(\Lambda_h)$, i.e. we have $$\mu^2(m_t) \sim \mu^2(\Lambda_h).$$Indeed this might have been guessed, since there is only one explicit physical scale in the theory, and no dynamic scales are generated from the electroweak scale up to the scale at which we expect the theory must be modified (which we'll come to shortly).<br />
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<b>12. A hierarchy problem</b></div>
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Nevertheless we have not solved a sort of the global naturalness problem. If one has $\mu^2(\Lambda_h) \lll \Lambda_h^2$ one might ask: <i>why?</i> In the standard model it is fair to argue that $\Lambda$ is an arbitrary regulator scale with no physical significance, $\Lambda_h$ is an arbitrary scale at which we specify the boundary condition, and that $\mu^2(\Lambda_h)$ is the only explicit mass scale in the theory, so why not? However many would argue that this is beside the point, since we expect that there is physics at a much higher scale, and it is actually this physics that we are concerned about. There seem to me to be two concerns here which are fundamentally distinct, although this distinction is not commonly made.<br />
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<li>The first concern is the violation of naive dimensional analysis. </li>
</ol>
This is what I think of as a "hierarchy problem", to be defined henceforth simply as <i>an unexplained hierarchy between energy scales in the theory</i> (this can be thought of as a sort of global naturalness problem). It should be emphasised here that this is <i>not</i> the sense in which people usually use the term hierarchy problem; usually it is used as a quasi-synonym for a naturalness problem for mass terms. Still, I find this definition and distinction useful and necessary, since it is possible to have a hierarchy problem (as defined) without having a (local) naturalness problem, as I will soon explain.<br />
<ol start="2">
<li>The second concern is that heavy new physics induces a naturalness problem for the Higgs mass. </li>
</ol>
For example, it could be the case that a physical mode exists at a very high scale, say $M$. The argument you often hear is that this makes $\Lambda$ physical, by setting the cutoff scale for the standard model at $\Lambda \sim M$, which then implies a $\delta\mu^2 \sim \frac{1}{(4\pi)^2} y_t^2 M^2$ correction which is also physical, so that the new mode (unless non-trivially ameliorated) has induced a naturalness problem. But I don't buy this argument. The term "cutoff scale" in this context is usually defined loosely as the scale at which the standard model fails to be a good description, or sometimes more precisely as the universal scale at which one defines higher dimension operators of the standard model effective field theory (making lower scale observables expansions in powers of $1/\Lambda$). But neither of these are the same thing as the cutoff regulator scale; the former are precise values and the latter is by definition an arbitrary value. Using the same term for each is the cause of some confusion. Instead of this hand-waving argument, we should take the more pragmatic approach of just writing down the theory with high scale physics included and checking when/if there's a naturalness problem. We will do this presently.</div>
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<b>13. The standard model with a hierarchy problem can be natural</b></div>
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What we should do is the following: write down the field theory with the high scale physics included, match this on to the effective field theory of the standard model at the threshold around $M$, and then write the Higgs mass-squared term $\mu^2(m_t)$ in terms of the input parameters of the high scale theory at scale $\Lambda_h>M$. When you do this you will find that an additional term appears in the $\mu^2$ renormalisation group equation above the scale $M$, i.e. $$\frac{d \mu^2}{d \log\Lambda_R} \sim \frac{1}{(4\pi)^2} y_t^2 \mu^2 + C M^2,$$where $C$ is some constant. There is also a threshold correction of similar order which appears when the theories are matched (in dimensionless schemes). The end result is you get something like $$\mu^2(m_t) \sim \mu^2(\Lambda_h) - C M^2 \log\left(\frac{\Lambda_h}{M}\right) + C_{thresh} M^2,$$where the first term is as in the pure standard model, the second term is the renormalisation group contribution, and the third term is the threshold correction contribution. <i>This</i> is why the Higgs has a <i>potential</i> naturalness problem: because it is not protected from corrections of this kind from any heavy new physics, and if $C M^2\gg \mu^2(m_t)$ then the input parameter $\mu^2(\Lambda_h)$ needs to be very precisely specified in order to realise the observed Higgs mass.</div>
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But this is exactly the point: it is $C M^2$ which is the quantity of interest, <i>not </i>$M^2$, and not (necessarily) anything to do with $y_t^2$. And what is $C$? Well it depends on the new physics: if it is a right-handed neutrino it is $\sim y_\nu^2 / (4\pi)^2$; if it is a particle with standard model gauge charges it is $\sim g^4/(4\pi)^4$; if it is another scalar it is $\sim \lambda_{HS}/(4\pi)^2$ (which could even be exactly zero in a technically natural way if the scalar is a gauge singlet); and if it is a stop (i.e. a top squark) it is $\sim y_t^2/(4\pi)^2$.<br />
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This brings us to a completely logical and obvious point: <i>the correction to (and the naturalness problem for) the Higgs mass induced by any heavy new physics depends on the strength at which that new physics couples or "talks" to the Higgs</i>. Therefore it is possible to have a field theory with a hierarchy problem, in the sense that new physics exists at a much higher scale than the electroweak scale, without having a naturalness problem (at least in the local sense), as long as that new physics couples sufficiently weakly to the Higgs.<br />
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<b>14. The standard model with <i>the </i>hierarchy problem can be natural</b></div>
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By <i>the</i> hierarchy problem I am specifically referring to the disparity between the electroweak scale and the scale at which we expect quantum gravitational effects become important, i.e. the Planck scale $\Lambda_{Pl}\sim 10^{18}~\text{ GeV}$. The hierarchy problem is often treated as synonymous with the naturalness problem for the Higgs. Certainly it is a hierarchy problem, at least as I have defined it, but does it imply a naturalness problem? I don't believe it necessarily does. Let me offer one argument.<br />
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The Planck scale, as far as I know, is only derived by dimensional analysis. The physical modes of gravity (or whatever they may be) may actually lie far below this scale, i.e. the theory of gravity might actually reside at a much lower scale (call it $\Lambda_G< \Lambda_{Pl}$). The apparent largeness of the Planck scale could then be explained by a small coupling strength (call it $C$) between standard model modes and gravitational modes, e.g. something like $\Lambda_{Pl} \sim \Lambda_G/C^2$. The physical correction to the Higgs mass should be proportional to the coupling strength, so something like $\delta \mu^2(m_t) \sim C^2 \Lambda_G^2$, which can be rewritten as $\delta \mu^2(m_t) \sim C^6 \Lambda_{Pl}^2$. Therefore, for sufficiently small $C$, there would be no naturalness problem.<br />
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To make a more precise analogy, consider if neutrino mass came from the Weinberg operator, $$ \frac{1}{\Lambda_N} \overline{(l_L)^c}\Phi\Phi^Tl_L .$$ The neutrino mass scale of $\sim 0.1\text{ eV}$ suggests $\Lambda_N\sim 10^{15} \text{ GeV}$ (which is why people immediately think of grand-unified theories). But in the simplest renormalisable neutrino mass model with right-handed neutrinos $N$ coupling to the Higgs via $y \overline{l_L} \tilde{\Phi} N$, we have$$\Lambda_N \sim \frac{M_N}{y^2}, \;\,\;\,\; \delta\mu^2(m_t) \sim \frac{y^2}{(4\pi)^2}M_N^2 \sim \frac{y^6}{(4\pi)^2} \Lambda_N^2.$$If $y^2 \lesssim 10^{-4}$, then the corrections to the Higgs mass are no larger than 1 TeV. This small value for $y$ is even technically natural. The neutrino mass seesaw requirement $y^2=m_\nu M_N / v^2$ translates this to $M_N\lesssim 10^7\text{ GeV}$.<br />
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We see that in this simple neutrino mass example: dimensional analysis implies an apparent very large scale $\sim 10^{15}\text{ GeV}$ in the theory; this apparent large scale could just be due to the appearance of a technically natural small coupling; and even the existence of a physical large scale $\sim 10^7\text{ GeV}$ in the renormalisable theory calculably does not introduce a naturalness problem. I see no logical reason why something like this could not also be the case for gravity. Indeed, from what I can tell this is exactly what happens in gravitational theories like e.g. softened gravity, or large extra dimensions, and surely others.<br />
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<b>15. The $y_t^2\Lambda^2$ correction</b><br />
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It is worth commenting that, in standard model plus heavy new physics theory, the quadratic divergence $\propto y_t^2\Lambda^2$ induced by the top quark loop does not appear in the equation relating $\mu^2(m_t)$ to the renormalised input parameter $\mu^2(\Lambda_h)$. Only contributions from heavy new physics appears. This is consistent with the interpretation of $\delta\mu^2 \propto y_t^2\Lambda^2$ as an unphysical contribution related to the regularisation procedure.</div>
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Often in the modern literature, proposed solutions to the Higgs naturalness problem (or a little naturalness problem) are motivated by showing that they contribute a term which cancels the $y_t^2\Lambda^2$ contribution. This may be a controversial statement, but I think this line of argument is unhelpful at best and misleading at worst. It's just that it mostly misses the real reason(s) why a given solution can solve a Higgs naturalness problem, and propagates the misconception that the quadratic divergence due to the standard model top quark is the problem which must be tamed by a negative contribution of the same order. The confusion is likely related to the fact that there is an actual physical contribution to the Higgs mass $\sim y_t^2\Lambda^2$ coming from new particles which couple to the Higgs with strength $y_t$ by construction in many of these solutions (e.g. stop quarks in supersymmetry or top partners in composite scenarios). Naturalness will demand that these particles be light because of this physical contribution, not because they need to save us from top quark divergences...</div>
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<b>16. The $y_t^2\Lambda^2$ correction in supersymmetry</b></div>
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Let me be more explicit by appealing to the usual argument for why supersymmetry solves the Higgs naturalness problem, and why it needs to appear at a fairly low scale. It goes something like the following. </div>
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<i>In a supersymmetric theory, for every fermionic quantum correction there exists an equal but opposite bosonic quantum correction (from the fermion's superpartner). For example, for the top quark we would have:$$\delta\mu^2 \sim \frac{1}{(4\pi)^2} y_t^2 \Lambda^2 - \frac{1}{(4\pi)^2} y_{\tilde{t}}^2 \Lambda^2,$$where the stop contribution cancels the top contribution by virtue of $y_t = y_{\tilde{t}}$. With no quantum correction to the Higgs mass there can be no naturalness problem. </i><br />
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<i>Since supersymmetry must be broken, this cancellation is only good above the (effective) supersymmetry breaking scale (approximately the stop mass scale), call it $\Lambda_{\rm SUSY}$. Below this scale the (uncancelled) top quark contribution dominates, therefore the quantum correction is, in toto,$$\delta\mu^2 \sim \frac{1}{(4\pi)^2} y_t^2 \Lambda_{\rm SUSY}^2.$$ Naturalness demands that this contribution be not much larger than the Higgs mass, which implies that </i><i>$\Lambda_{\rm SUSY}$</i><i> should be not much larger than the TeV scale.</i></div>
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This argument gives the right answer, i.e. that supersymmetry at or below the TeV scale can solve a Higgs naturalness problem, but it is totally misleading. The claim is that the top quark quadratic divergence is the problem that needs to be tamed, and that the taming is done by the stop. But this is not really the reason why supersymmetry solves a potential naturalness problem for the Higgs (nor the reason why there needs to be a stop).</div>
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<b>17. Supersymmetry can solve a Higgs naturalness problem <br />(but probably not in the way you've been taught)</b></div>
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Let me offer an alternative argument which is fully consistent with the picture sketched above (in terms of the renormalised parameters). In this picture the real worry for the Higgs mass is corrections from heavy new physics which is sufficiently strongly coupled to the Higgs. In particular, a heavy particle of mass $M$ introduces a term $\sim C M^2$ into the renormalisation group equation for the Higgs mass, which results in similarly sized terms in the equation for the observed Higgs mass when written in terms of the high scale input parameters. What supersymmetry does for you is ensure that another particle exists (the supersymmetric partner) which contributes another term $\sim -C M^2$ to the renormalisation group equation which cancels the first contribution. In fact it ensures that this property holds to <i>all</i> loop levels and at <i>all </i>energy scales. For this to work in fact requires that <i>every</i> particle must have a supersymmetric partner, not just the heavy particle. This is because, schematically, as you draw higher-loop Feynman diagrams involving the heavy particle you will eventually find one with also e.g. a top quark involved, and hence a loop-suppressed contribution to the Higgs mass $\propto y_t^2 M^2$, or else a contribution to some scalar quartic $\propto y_t^2$ which threatens stability under renormalisation group flow, etc. To cancel these contributions you find that you need a supersymmetric partner for the top. And so on for every other particle. This remarkable result is embodied in the supersymmetric non-renormalisation theorem, which ensures that the renormalisation group equation for each parameter in a supersymmetric theory, <i>including for the mass parameters</i>, is proportional to the parameter itself, i.e. they are always technically natural. So in <i>any</i> supersymmetric theory, once you set a mass parameter at the high scale, it will always be safe from large quantum corrections from heavy new physics (including in theories with very heavy states which couple relatively strongly to the Higgs, like in grand unified theories). This is, for me, the much more profound and completely non-trivial reason why supersymmetry can solve a Higgs naturalness problem (and why there needs to be a stop).</div>
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Of course, in nature, supersymmetry is broken, so this can't be the entire story. If nature is fundamentally supersymmetric then the standard model superpartners must have large enough masses to have thus far evaded searches at e.g. the Large Hadron Collider. This is a potential problem for naturalness of the Higgs mass. For example, in the (softly broken) minimal supersymmetric model the Higgs mass-parameter (named here $\mu_{\rm SM}$) is given at tree level by$$\mu_{\rm SM}^2 = |\mu|^2+\mu_{H_{u}}^2,$$ where $\mu$ is the supersymmetric $\mu$-parameter and $\mu_{H_{u}}^2$ is a soft-breaking parameter. Naturalness will loosely demand that the parameters on the right-hand side are not too large so as to require a precisely specified cancellation. But here $\mu$ is also the approximate scale for the higgsino masses, so this would imply light higgsinos. Beyond tree level there are radiative contributions primarily from the stop and gluino sectors, and renormalisation group and threshold corrections to $\mu_{H_{u}}^2$ of the order $\frac{y_t}{(4\pi)^2}m_{\rm stop}^2$. Naturalness will loosely demand that these corrections be sufficiently small as well. This is the argument for light stops (i.e. <i>not</i> because the stop is needed to start cancelling off a quadratic divergence from the top quark). Then gluinos correct the stop mass, so naturalness requires light enough gluinos, and so on. In any case, neither higgsinos, nor stops, nor gluinos have been seen at the LHC, threatening natural supersymmetry.<br />
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I am no expert in Higgs mass calculations from high scale supersymmetric parameters, so I will stop here. Broken supersymmetry is not necessarily an impediment for supersymmetry as a solution to a potential Higgs mass naturalness problem. Still, if it is the solution, the supersymmetric standard model partners must be realised at a low enough energy for the above mentioned reasons. To know exactly how heavy they can be before violating naturalness requires actually calculating the Higgs mass in terms of the high scale input parameters, quantifying the dependence on those input parameters, and determining when/if those parameters are required to be "precisely specified". This exercise has become its own industry for papers in high energy physics. Unfortunately many approximations are made in the map from inputs to Higgs mass (e.g. constraining the parameter space), and there is not even an agreed upon approach for measuring the degree of naturalness. This causes its own set of problems, to be discussed after the next section, where I have a small bone to pick.</div>
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<b>18. Supersymmetry does not solve the hierarchy problem</b></div>
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The minimal supersymmetric standard model does not explain the <i>origin</i> of the $\mu$ parameter (or $\mu_{H_u}^2$ for that matter). Therefore, and by my definition, one has not eliminated the hierarchy problem (i.e. why is $\mu \lll \Lambda_{Pl}$?), or any other hierarchy problem which might exist if heavy new physics is present (e.g. a grand unification scale). This has its own name: "the $\mu$ problem".<br />
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This is not to say the hierarchy problem cannot be answered within the supersymmetric paradigm. There are some very satisfactory possible explanations for the origin of $\mu$ in extended models. The point to make though is that you need such an explanation <i>in addition</i> to needing supersymmetry. For example, a common explanation is to have $\mu=0$ at high scale, imposed by some global or scale symmetry, only to be made non-zero when some dynamical scale is generated (e.g. by spontaneous symmetry breaking) at a comparatively high scale, which then induces a small $\mu$ term via some dimensionally suppressed operator. Something like this arises if the dynamical scale is otherwise decoupled and only communicated to $\mu$ via even higher scale physics (e.g. gravity or otherwise). This is an excellent example of how a fully natural hierarchy can exist in a quantum field theory. In this setup the $\mu$ parameter has its origin in the high dynamical scale, and its relative smallness (and the failure of naive dimensional analysis) is just explained by a suppressed coupling between the scales.</div>
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<b>19. The problems with measuring naturalness</b></div>
<b><br /></b>So far our discussion of naturalness has been intentionally non-rigorous. We have talked about parameters being precisely specified, in both local and global senses, without really explaining what this might mean quantitatively. Indeed, many questions remain, for example: <i>In what parameters should we measure perturbations ($x$, $x^2$, $\log(x)$, ...)? What constitutes an unacceptably large change in the observables? Do we measure perturbations in all parameters, including the already measured parameters, or just the unmeasured ones? Does the answer depend on the way in which I write down my theory? What is the "volume" of the original parameter space? Is it right to exclude theories which are non-perturbative just because I cannot calculate in them?</i> And so on.<br />
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There is a tendency in the field to define naturalness measures intuitively. For example, the most popular is the Barbieri-Giudice fine-tuning measure which compares percentage changes in an input(s) versus those in the Higgs mass-squared parameter (or the Higgs mass, or $Z$ mass, or similar):$$\Delta_{\mathcal{X}_I} = \left|\frac{\partial\log\mu^2}{\partial\log\mathcal{X}_I}\right|,$$where $\mathcal{X}_I$ is some high scale "input" parameter, usually one of the Lagrangian parameters or a high scale observable. If this measure is sufficiently large then you would start to call the theory unnatural, since a small change in the input is inducing a large change in the observable. When simple intuitive measures return non-sensical results in special cases, or when they become too involved to fully calculate, they might be extended/patched/simplified in various ways which are again often motivated by intuitive arguments. Popular ones are, for example,$$\Delta = \max\limits_{\mathcal{X}_I}\left\{ \left|\frac{\partial\log\mu^2}{\partial\log\mathcal{X}_I}\right| \right\},\text{ and}$$ $$\Delta = \sqrt{ \sum\limits_{\mathcal{X}_I} \left(\frac{\partial\log\mu^2}{\partial\log\mathcal{X}_I}\right)^2 },$$where the maximisation/sum is often performed over a subset of the parameters for simplicity. The end result of all this is a plethora of measures within the literature which can return very different results even for the very same model, and no clear "best" measure or even a methodology by which to categorise/compare the measures. Since they are motivated intuitively, it is not clear what the assumptions are behind them, and as such no clear way to address questions like in the first paragraph. Put simply, they are just rather arbitrary. A common excuse is the following: <i>well, naturalness is a subjective concept anyway, why shouldn't our measures also be? </i>This to me is entirely unsatisfactory – we can do better.<br />
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I make this claim because the last paragraph follows the arc of my own study and understanding of naturalness measures. In studying naturalness even within very minimal extensions of the standard model I found that the simple measures would sometimes fail to identify the fine-tuning in certain areas of parameter space which were clearly fine-tuned (regions which resembled what is known as a "Veltman throat"). Sometimes it can be argued that this goes away when the calculations are performed at higher loop order. Other times it remains. It doesn't take much brainstorming effort to intuitively identify a number of possible ways to extend the simple measures in order to capture the fine-tuning, but it is not at all clear which is the "proper" way. And when you're stuck, you go back to first principles. I asked: what are my assumptions? what exactly do I mean by naturalness? and so on, much of which resulted in what has already been written. The key turning point in my understanding of naturalness measures in particular was the discovery of <a href="https://arxiv.org/abs/1204.4940">a paper</a> by Sylvain Fichet: "Quantified naturalness from Bayesian statistics"...<br />
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<b>20. The Bayesian approach to measuring naturalness</b></div>
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Bayesian probability is a framework that has all the ingredients to capture and quantify the subjective part of naturalness and leave the rest up to the mathematics in a completely consistent way. One can write down quantities which act just like naturalness measures, but with the appealing property of having a precise meaning in terms of Bayesian statistics. This chapter is rather loose and a bit technical, but I want to provide a sketch in order to give you a taste of how this works, because it seems to me this is just the right way to think about naturalness.<br />
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Take some high scale model $\mathcal{M}$ of particle physics. The question of naturalness is reframed: <i>how probable is the low scale standard model given this high scale model?</i> Mathematically, that is, you are interested in$$Pr(\mathcal{O}=\mathcal{O}_{exp} | \mathcal{M}),$$where $\mathcal{O}$ is the set of observables. This is what is called the "Bayesian evidence" for $\mathcal{M}$ given a set of prior beliefs on the model inputs,$$B(\mathcal{M}) := Pr(\mathcal{O}=\mathcal{O}_{exp} | \mathcal{M}) = \int Pr(\mathcal{O}=\mathcal{O}_{ex} | \mathcal{I} )\; Pr( \mathcal{I} )\; d\mathcal{I},$$where $\mathcal{I}$ is the set of input parameters and $Pr( \mathcal{I})$ the set of prior beliefs. The Bayesian evidence is a very good place to start deriving a naturalness measure. All the subjectivity is captured and quantified in the prior densities (and implicitly the volume of the input parameter space). If you work through the mathematics (and assuming flat prior densities) you find that the Bayesian evidence becomes something like$$B(\mathcal{M}) \sim \frac{1}{\sqrt{\left|{\rm det}\left(JJ^T\right)\right|}},$$where $J$ is the matrix $J_{ij} = \partial\mathcal{O}_i/\partial\mathcal{I}_j$. (The origin of this term lies in coordinate transformations and the induced metric on the input space submanifold carved out by the requirement that observables match experiment).<br />
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Now, as argued above, we can define our input parameters with respect to the renormalised high scale model Lagrangian parameters, call them $\{\mathcal{X}_I\}$. What about our priors? Requiring that the result not be dependent on units or parameter rescalings suggests that we should take a flat prior in the $\log$ of the inputs (since $\partial\log\mathcal{X} = \partial\mathcal{X}/\mathcal{X}$); this is a sort of "maximally agnostic" prior. Similarly, we identify the set of observables with the logged set of renormalised standard model Lagrangian parameters, call them $\{\log\mathcal{X}_O\}$. The Bayesian evidence becomes$${\small<br />
B(\mathcal{M}) \sim<br />
\frac{1}<br />
{\sqrt{\left|{\rm det}\left[<br />
\left(<br />
\begin{array}{ccc}<br />
\frac{\partial\log\mathcal{X}_{O_1}}{\partial \log\mathcal{X}_{I_1}} & \cdots & \frac{\partial\log\mathcal{X}_{O_1}}{\partial \log\mathcal{X}_{I_n}} \\<br />
\vdots & \ddots & \vdots \\<br />
\frac{\partial\log\mathcal{X}_{O_m}}{\partial\log \mathcal{X}_{I_1}} & \cdots & \frac{\partial\log\mathcal{X}_{O_m}}{\partial\log \mathcal{X}_{I_n}}<br />
\end{array}<br />
\right)<br />
\left(<br />
\begin{array}{ccc}<br />
\frac{\partial\log\mathcal{X}_{O_1}}{\partial \log\mathcal{X}_{I_1}} & \cdots & \frac{\partial\log\mathcal{X}_{O_1}}{\partial \log\mathcal{X}_{I_n}} \\<br />
\vdots & \ddots & \vdots \\<br />
\frac{\partial\log\mathcal{X}_{O_m}}{\partial\log \mathcal{X}_{I_1}} & \cdots & \frac{\partial\log\mathcal{X}_{O_m}}{\partial\log \mathcal{X}_{I_n}}<br />
\end{array}<br />
\right)^T<br />
\right]<br />
\right|}}<br />
}$$So you're now starting to see something which looks like the inverse of a generalised version of the Barbieri-Guidice measure. That is what you expect, since low evidence should correspond to high fine-tuning (or low naturalness). And this quantity is calculable (if the model is perturbative). The renormalisation group equations, together with the threshold corrections at the interfaces of effective field theories, define the map which relates the high scale inputs to the standard model observables at low scale. With this map in hand you can start turning the crank: you just calculate to the highest loop level you can (or are willing to) and solve the resulting coupled set of differential equations with boundary conditions to evaluate $\left|{\rm det}\left(JJ^T\right)\right|$ at different points in the input parameter space.<br />
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How do you interpret the number you get? Actually it is not so straight forward to interpret the Bayesian evidence alone. In the above equations I left off volume factors and the integration over input space. This integration is complicated by the fact that points in the theory of interest may hit non-perturbative regimes (where we do not yet know how to calculate). I left these details off because there is a way to "bypass" the complications by taking <i>ratios</i> of Bayesian evidences. This can be done between models, within the one model for different inputs, or for different priors, and can be set up to capture the local or global naturalness problem. Whatever is chosen, the interpretation of the ratio is a well-defined one: it is a Bayesian model comparison which captures the relative evidence for one model over another. For example, to study naturalness of the Higgs mass in <a href="https://arxiv.org/abs/1607.07446">the paper</a> for which I was a co-author, we found it useful to compare the models where the Higgs mass-squared parameter was taken either as a low scale "phenomenological" input parameter, or as a high scale input parameter (with the same prior). This ratio had some nice properties where much of the matrix algebra cancelled to unity, an intuitive Barbieri-Giudice-like measure was reproduced in a relevant limit, and all the previously uncaptured areas of fine-tuning were smoothed over.<br />
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The particulars of that approach are beyond the scope of this blog post (and irrelevant, really). What I wanted to give was a flavour of the Bayesian approach to naturalness. Unfortunately this approach is still a minority in the literature. There are probably two main reasons for this. The first reason is just that it is not as straight-forward as writing down an intuitive measure. The second reason is uneasiness about dependence on the priors; the common objection is the following: <i>clearly your answer depends on the priors, and how do you know that the high scale physics implies e.g. flat priors?</i> But that's exactly the point – you don't and you can't. What you <i>have</i> done is derive a naturalness measure from an underlying framework with a well-defined meaning and with all your assumptions rolled into the priors in a clear, explicit (and optionally maximally agnostic) way. That is in my opinion much more transparent than just using a measure written down intuitively. And it makes clear that you <i>are</i> in fact making assumptions about the high scale physics. Naturally! For all these reasons I find the approach extremely satisfying.<br />
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<b>21. A kind of conclusion</b></div>
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I don't know if anyone will read this post, but I hope that they do, and that they share it and challenge it. It seems ridiculous to me that the field of physics beyond the standard model, which (it is probably fair to say) has been motivated primarily by naturalness arguments for the past decades, is so loose and so full of misconceptions about naturalness. I guess it is just the foreseeable consequence of a lack of clear, physical, rigorous, well-defined, and agreed upon definitions. There may have been a time when the majority of the field understood the nuances, but this does not seem to be the case now, and certainly not at the graduate level, where our exposure usually amounts to the same parroted introduction slide explanation in terms of a top quark induced quadratic divergence. Not only does this undersell the more profound reason why e.g. supersymmetry is a potential solution, but it propagates the incorrect ideas that the top quark itself is the problem, and that it is the scale of new physics alone which sets the level of the problem (i.e. not involving the coupling strength).<br />
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At a time when the Large Hadron Collider is challenging the established wisdom on naturalness, surely it is time to take stock and sturdy up its foundations? If you agree, please share this and start the dialogue. I sure hope so, but maybe not. So it goes.</div>
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Bluejayhttp://www.blogger.com/profile/06935684943024856641noreply@blogger.com24tag:blogger.com,1999:blog-959149188511266512.post-37205712889368908892016-06-05T15:21:00.003+10:002016-06-05T15:21:32.235+10:00Warsaw Workshop on Non-Standard Dark MatterFor the last few days I've been at the Warsaw Workshop on <a href="http://indico.fuw.edu.pl/conferenceDisplay.py?confId=45">Non-Standard Dark Matter</a>. It's been very enjoyable! Plenty of interesting ideas, coffee, and social events. Yesterday I gave a short talk, trying to make the case for a dark matter direct detection search for the sidereal modulation signature. The general idea is that, if dark matter has self-interactions, the dark matter wind which strikes the Earth will interact with any Earth-captured dark matter, leading to a non-trivial spatial distribution which terrestrial detectors traverse throughout the day. I share the slides below this post. If nothing else you should click through to see some entertaining magnetohydrodynamic simulation animations!<br />
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By the way, as of this writing ATLAS+CMS have recorded about 2+2/fb of data (or 20 diphotons in alternative units):<br />
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<a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhUvvEqRnjfytiQeYdwwsIsu1YOIJenn15UXHbwo_cZJpJwlbacOwH72KdKukefMmUoNSHQkvF-Jh3XgYVa3j617Ed52w_L6jyQIGHnVAKwXbtq279-4MEOa2xOFYXnXpmShMeJ9ynzl2c/s1600/sumLumiByDay.png" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" height="143" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhUvvEqRnjfytiQeYdwwsIsu1YOIJenn15UXHbwo_cZJpJwlbacOwH72KdKukefMmUoNSHQkvF-Jh3XgYVa3j617Ed52w_L6jyQIGHnVAKwXbtq279-4MEOa2xOFYXnXpmShMeJ9ynzl2c/s200/sumLumiByDay.png" width="200" /></a><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEikwuNWKEwInqe-xDIDPPxmR0AO5rnTqApZg4e5YxseaYpo4z_Ud0tj_gGfJg1BH23WKJbMHHbSmE3XRRkHbUDWKFJ3u7q82N80hql6dK1oQQHTgZ9beblw8ZPyvisniYdqI93ITMVvjuA/s1600/int_lumi_per_day_cumulative_pp_2016OnlineLumi.png" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" height="150" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEikwuNWKEwInqe-xDIDPPxmR0AO5rnTqApZg4e5YxseaYpo4z_Ud0tj_gGfJg1BH23WKJbMHHbSmE3XRRkHbUDWKFJ3u7q82N80hql6dK1oQQHTgZ9beblw8ZPyvisniYdqI93ITMVvjuA/s200/int_lumi_per_day_cumulative_pp_2016OnlineLumi.png" width="200" /></a></div>
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We're quickly moving toward the position we were by Christmas last year (about 3+3/fb including the CMS $B=0$ data). If the 750 GeV diphoton resonance prevails in the new data we hope to know by the <a href="https://www.ichep2016.org/">ICHEP</a> on August 3-10. <a href="http://arxiv.org/pdf/1604.06446.pdf">Some authors</a> have taken to calling the would-be particle Ϝ, which is the archaic Greek letter "digamma" -- very fitting! We will see yet if this name becomes lore... I also quite like the following perhaps future update of the PDG <a href="http://arxiv.org/abs/1605.09401">from Strumia</a>:</div>
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<a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgkfh74oFXUKiAqZN-f_Gl___2FXQbs2DY8D2gPK0R1RtEHEK-Ry0TF5pAzcVO_at1ItxMWMPErJwT0KIhmJOk0L9faulJ7CNHgK6aAdJ_wgqzgA_iSyWIu8tt_1CKE5nsAYdP-nFbNzWo/s1600/Screenshot+from+2016-06-05+15%253A18%253A23.png" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" height="321" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgkfh74oFXUKiAqZN-f_Gl___2FXQbs2DY8D2gPK0R1RtEHEK-Ry0TF5pAzcVO_at1ItxMWMPErJwT0KIhmJOk0L9faulJ7CNHgK6aAdJ_wgqzgA_iSyWIu8tt_1CKE5nsAYdP-nFbNzWo/s400/Screenshot+from+2016-06-05+15%253A18%253A23.png" width="400" /></a></div>
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<b>Slides</b></div>
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<iframe allowfullscreen="true" frameborder="0" height="569" mozallowfullscreen="true" src="https://docs.google.com/presentation/d/1-D0ge0f1Ia1xpBNaRSELFczqE8xfqy7Jv7ZCYc7F0YU/embed?start=false&loop=false&delayms=5000" webkitallowfullscreen="true" width="650"></iframe><br />
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<br />Bluejayhttp://www.blogger.com/profile/06935684943024856641noreply@blogger.com2tag:blogger.com,1999:blog-959149188511266512.post-90642431702804168952016-04-24T19:55:00.003+10:002016-04-24T19:55:34.226+10:00Wrap-up<div>
Readers might have noticed that this blog has slowed down lately. The reason is that I am in a transition period at the moment, wherein I hope to: see to completion three collaborative projects, attend two conferences in Europe (Warsaw Workshop on Non-Standard Dark Matter, and The Lindau Nobel Laureate Meeting), make it back in time for SUSY2016 in Melbourne, complete my PhD thesis (by August 1), move into a new position juggling research with industry work, and also go on a belated honeymoon... hence the blog will have to go on the backburner for now. In order to keep this format up I need to be in a stable routine, which was the case for the last year or so, but currently is not. Updates might still be made in the coming months, though certainly not in this same format. Until then...!<br />
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<li>LHC had its <a href="https://youtu.be/ig8TD7L0kpk">first proton beam</a> on 25th March, and today had <a href="https://twitter.com/CERNpress/status/723645676580679680">first stable</a> 13 TeV collisions!</li>
</ul>
<ul>
<li><a href="https://indico.cern.ch/event/351843/contributions/828673/">Belle has released</a> a preliminary measurement of an angular observable in $B\to K^*\mu\mu$ which LHCb <a href="http://syymmetries.blogspot.com.au/2015/03/friday-wrap-up-lhc-delay-b-to-k-higgs.html">has consistently been</a> seeing a discrepancy with. Belle see the same thing:<br /><br /><div class="separator" style="clear: both; text-align: center;">
<a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjnqxrNcYpy_BR6NfEAJnhqn9WwikKYvRWF5_Z4U6X3maMItwCiIuMaLCpcqyIh0uVmwdK6MYpQWK0YjHtFKR8aEOkKeuVmFLkVFYSgmqyVTJYBeNEP68W4kZEiGee0rFDIfcJ8_glssVk/s1600/Screenshot+from+2016-04-24+16%253A26%253A16.png" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" height="298" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjnqxrNcYpy_BR6NfEAJnhqn9WwikKYvRWF5_Z4U6X3maMItwCiIuMaLCpcqyIh0uVmwdK6MYpQWK0YjHtFKR8aEOkKeuVmFLkVFYSgmqyVTJYBeNEP68W4kZEiGee0rFDIfcJ8_glssVk/s400/Screenshot+from+2016-04-24+16%253A26%253A16.png" width="400" /></a></div>
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</li>
<li>Four 750 GeV diphoton papers <a href="http://journals.aps.org/prl/pdf/10.1103/PhysRevLett.116.150001">were published</a> in Physical Review Letters this week.</li>
</ul>
<ul>
<li>April Fools came and went; see CERN's <a href="http://home.cern/about/updates/2016/04/sonified-higgs-data-show-surprising-result">effort here</a>, <a href="http://news.fnal.gov/2016/04/auntie-proton/">Fermilab</a>, arXiv <a href="http://arxiv.org/abs/1603.09703">here</a>, and <a href="http://theoryandpractice.org/downloads/files/supersplit_750.pdf">return of</a> supersplit supersymmetry, this time (of course) linked to the 750 GeV diphoton excess.</li>
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<ul>
<li>CMS publicly <a href="http://cms.web.cern.ch/news/cms-releases-new-batch-research-data-lhc">released 2.5/fb</a> of 7 TeV proton-proton collision data.</li>
</ul>
<ul>
<li>Dark Matter at the LHC Workshop ran from 30 March to 1 April (<a href="https://indico.cern.ch/event/342623/">indico</a>). LHCski: A first discussion of 13 TeV results, ran from 10-15 April (<a href="https://indico.cern.ch/event/351843/timetable/#20160411.detailed">indico</a>).</li>
</ul>
<ul>
<li>Links without thinks:</li>
<ul>
<li>Matthew Buckley via Boston Review: The <a href="http://bostonreview.net/books-ideas/matthew-buckley-search-new-physics-cern">Search for</a> New Physics at CERN, and The <a href="https://bostonreview.net/books-ideas/matthew-buckley-search-new-physics-cern-part-2">Hitchhiker's Guide</a> to Quantum Field Theory.</li>
<li>CERN: In Theory: <a href="http://home.cern/about/updates/2016/04/theory-which-came-first">Which came</a> first…?</li>
<li>Backreaction: Why is Lorentz-invariance <a href="http://backreaction.blogspot.com.au/2016/04/dear-dr-b-why-is-lorentz-invariance-in.html">in conflict with</a> discreteness?</li>
<li>Quanta: Physicists Hunt for the <a href="https://www.quantamagazine.org/20160419-string-inflation-triangles/">Big Bang’s Triangles</a>.</li>
<li>Quanta: Debate Intensifies Over <a href="https://www.quantamagazine.org/20160412-debate-intensifies-over-dark-disk-theory/">Dark Disk</a> Theory.</li>
</ul>
</ul>
<ul>
<li>In audio/video media:</li>
<ul>
<li>In Particular shorts: <a href="https://youtu.be/i0_sKMttxEY">Graviton</a>. [7:14]</li>
<li>Art McDonald via Perimeter Institute: A Deeper Understanding of the Universe <a href="https://youtu.be/hLp15co2D-A">from 2 km</a> Underground. [1:16:53]</li>
<li>Jernej Kamenik via Laitn American Webinars: Update on the LHC <a href="https://youtu.be/v14Amv9pg0M">diphoton excess</a>. [1:11:58]</li>
<li>Nima Arkani-Hamed via IAS Princeton: <a href="https://youtu.be/1HRdqNcgOOo">The Future</a> of Particle Physics. [1:43:42]</li>
<li>David Kaplan via Quanta: Is <a href="https://youtu.be/wDYd4nd0Fjg">That 'Bump'</a> a New Particle? [2:25] </li>
<li>Don Lincoln via Fermilab: Theoretical physics: <a href="https://youtu.be/TYTQm7t3I38">insider's tricks</a>. [8:31]</li>
<li>Perimeter Institute: Canadian Prime Minister <a href="https://youtu.be/4ZBLSjF56S8">Justin Trudeau</a> Explains Quantum Computing. [1:08]</li>
<li>Vsauce: How To <a href="https://youtu.be/SrU9YDoXE88">Count Past</a> Infinity. [23:45]</li>
</ul>
</ul>
</div>
Bluejayhttp://www.blogger.com/profile/06935684943024856641noreply@blogger.com2tag:blogger.com,1999:blog-959149188511266512.post-64935787752574211482016-03-25T15:49:00.000+11:002016-04-07T21:34:07.971+10:00Friday wrap-up: Moriond...The 50th anniversary Rencontres de Moriond (<a href="https://indico.in2p3.fr/event/12279/other-view?view=standard">electroweak indico</a>, <a href="https://twitter.com/_Moriond_">twitter</a>, <a href="https://twitter.com/hashtag/moriond?src=hash">hashtag</a>) was on over the past few weeks. Here's the updated logo [credit <a href="https://indico.in2p3.fr/event/12279/session/12/contribution/110/material/slides/1.pdf">Strumia</a>]:<br />
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<a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEinTpOf7ZsbatzrmFq99rAeGyH-cl8M5J7-ORKicBXOib9Q4y7kEakfDVjRsE9tS3Bbe_8sCQp3YImvoBwlKCf5YUqKzGlo-0XLfa6ouB5v_ZAS43u2KUWqZBNxNS_k_c4FPqs9kq26DMs/s1600/Screenshot+from+2016-03-25+12%253A11%253A30.png" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" height="161" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEinTpOf7ZsbatzrmFq99rAeGyH-cl8M5J7-ORKicBXOib9Q4y7kEakfDVjRsE9tS3Bbe_8sCQp3YImvoBwlKCf5YUqKzGlo-0XLfa6ouB5v_ZAS43u2KUWqZBNxNS_k_c4FPqs9kq26DMs/s200/Screenshot+from+2016-03-25+12%253A11%253A30.png" width="200" /></a></div>
<div style="text-align: center;">
<br />
<div style="text-align: left;">
Not sure how the 7 got in there... probably insignificant.</div>
</div>
<ul>
<li>The most anticipated results were updates on the 750 GeV <a href="http://syymmetries.blogspot.com.au/2015/12/friday-wrap-up-diphoton-excess-no.html">diphoton saga</a>. Slides from ATLAS and CMS are <a href="https://indico.in2p3.fr/event/12279/session/12/contribution/163/material/slides/1.pdf">here</a> and <a href="https://indico.in2p3.fr/event/12279/session/12/contribution/218/material/slides/0.pdf">here</a>. <br /><br />There are excellent detailed write-ups at <a href="http://resonaances.blogspot.com.au/2016/03/diphoton-update.html">Résonaances</a> and <a href="http://www.physicsmatt.com/blog/2016/3/18/tdu3j18n86e01bd4a8l8u5flqdifce">PhysicsMatt</a> already, and I don't have much to add to these (for pop-sci articles see e.g. <a href="https://www.theguardian.com/science/2016/mar/18/excitement-grows-over-large-hadron-colliders-possible-new-particle-lhc">Guardian</a>, <a href="http://www.symmetrymagazine.org/article/bump-watch-2016">symmetry</a>, <a href="http://www.scientificamerican.com/article/hints-of-new-lhc-particle-get-slightly-stronger/">Scientific American</a>). You should read them, if you haven't. In short, with the addition of new "B=0" data from CMS and an updated analysis from ATLAS, the excess is not going away. Below I reproduce one of the third-party combination plots published on <a href="http://www.physicsmatt.com/blog/2016/3/18/tdu3j18n86e01bd4a8l8u5flqdifce">PhysicsMatt</a> which tells some of the story. On the left is the combination of previous data, and on the right after the Moriond update, assuming the <a href="https://indico.in2p3.fr/event/12279/session/12/contribution/110/material/slides/1.pdf">Volksmodel</a> $gg\to S\to \gamma\gamma$ and a narrow width:<br /><br /><div class="separator" style="clear: both; text-align: center;">
<a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgK6IhBhaOl7ort3kBQBCYDGkO_KJy9xPz9yTkBiBFvT44-9PMFAbnklgoLEo5XqyuS-qvAgqgP4UFHI3Iwa_ioUP6mXcsgYcjFm4hmq0SiNreFgCky-L6i3MX0-XOmyb2ACCu-c2qbzww/s1600/Screenshot+from+2016-03-25+12%253A56%253A38.png" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgK6IhBhaOl7ort3kBQBCYDGkO_KJy9xPz9yTkBiBFvT44-9PMFAbnklgoLEo5XqyuS-qvAgqgP4UFHI3Iwa_ioUP6mXcsgYcjFm4hmq0SiNreFgCky-L6i3MX0-XOmyb2ACCu-c2qbzww/s640/Screenshot+from+2016-03-25+12%253A56%253A38.png" width="560" /></a></div>
<div style="text-align: center;">
<br /></div>
One can see by eye that the reanalysis of the ATLAS 8 TeV data shows it is more consistent with a $gg\to S$ 13 TeV excess than previously believed, and there's an excess in the new CMS 13 TeV data in the right ballpark. Taken together this adds a little fuel to the fire.<br /><br />As well, there are strong rumours that ATLAS are sitting on an analysis in which they relax some of their cuts (increasing acceptance of events), and that this alone bumps up the local (global) significance of the excess to ~4.7σ (>3σ) [see e.g. <a href="http://resonaances.blogspot.com.au/2016/03/diphoton-update.html">Résonaances</a> and comment section]. If this is true then hep-ph might as well become hep-γγ...<br /><br />For your interest see below some (obviously biased) surveys in the twittersphere. Clearly people are taking this seriously. If the rumoured ATLAS analysis is true I would give the 750 GeV excess a dice throw at sticking around.<br /><div style="text-align: center;">
<blockquote class="twitter-tweet" data-lang="en">
<div dir="ltr" lang="en">
Bets are circulating if the 750 GeV excess is real or not. What's your take?</div>
— RencontresdeMoriond (@_Moriond_) <a href="https://twitter.com/_Moriond_/status/712017015763038208">March 21, 2016</a></blockquote>
<blockquote class="twitter-tweet" data-lang="en">
<div dir="ltr" lang="en">
What are the odds you place on the diphoton excess being real new physics? (Odds are in favor of this being real).</div>
— Matthew Buckley (@physicsmatt) <a href="https://twitter.com/physicsmatt/status/713007452715884547">March 24, 2016</a></blockquote>
<br />
<script async="" charset="utf-8" src="//platform.twitter.com/widgets.js"></script>
<script async="" charset="utf-8" src="//platform.twitter.com/widgets.js"></script></div>
</li>
</ul>
<ul>
<li>If you're out of ideas for how to explain the excess, then maybe you can find inspiration at <a href="http://snarxiv.org/hep-750gev/">snarXiv</a>.</li>
</ul>
<ul>
<li>About a month ago D0 <a href="http://arxiv.org/abs/1602.07588">announced observation</a> of a tetraquark $X(5568)\to B_s^0\pi^\pm$ state. It received quite a bit <a href="http://www.symmetrymagazine.org/article/fermilab-scientists-discover-new-four-flavor-particle">of press</a>. Here's the plot from the D0 preprint:<br /><br /><div class="separator" style="clear: both; text-align: center;">
<a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjBbogwlUbPLIEplD2l1070QSkUZB7qmftULx_N1eTmntvaQeJq3oyeDgVx_P0comF8Uf49KhtIMHskGRF4qFBE-3H4H9NIeoBxyYw2Pnm9pmyLD_ex_-gOos3WUqFHsOeNJQMn11o93y0/s1600/Screenshot+from+2016-03-25+11%253A46%253A55.png" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" height="640" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjBbogwlUbPLIEplD2l1070QSkUZB7qmftULx_N1eTmntvaQeJq3oyeDgVx_P0comF8Uf49KhtIMHskGRF4qFBE-3H4H9NIeoBxyYw2Pnm9pmyLD_ex_-gOos3WUqFHsOeNJQMn11o93y0/s640/Screenshot+from+2016-03-25+11%253A46%253A55.png" width="329" /></a></div>
<br />At Moriond LHCb announced that they see no evidence for such a tetraquark state (<a href="http://moriond.in2p3.fr/QCD/2016/WednesdayMorning/Gandini.pdf">slides 22-24 here</a>). A few days ago there was an <a href="https://indico.cern.ch/event/509820/attachments/1244766/1837209/LHC_Seminar_Pappagallo_22032016.pdf">LHC Seminar</a> on the analysis. From what I can gather, there is some talk of bias introduced by a "cone cut" in the D0 analysis. In the <a href="http://cds.cern.ch/record/2140095/">Conf Note</a> LHCb write:<br /><br /><i>In the D0 analysis, a requirement is imposed on the opening angle between the $B^0_s$ candidate and the companion pion in the plane of pseudorapidity and azimuthal angle [$\Delta R$]... No such requirement is imposed here, as $\Delta R$ is strongly correlated with $Q$ value and, when combined with kinematic requirements imposed by the LHCb detector acceptance, a cut on this variable can cause broad peaking structures.</i><br /><br />There is speculation that this might have introduced some spurious shape or impacted the statistical interpretation somehow for D0. I find the following slide from the seminar rather telling.<br /><br /><div class="separator" style="clear: both; text-align: center;">
<a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjnIhK6HMtYRGJ_r-Cr1sIFZe36jJLXa5bHKEH3VREaYKpNeDTOli8wS4S_zgGIg5X63BUeLQVPv3AKlbN64e6x5LRcKKzLmO3P7YcF1RVmew0L4Cnvjlj1UIhOgvlwpsC7C7z_KhZc5CE/s1600/Screenshot+from+2016-03-25+11%253A57%253A02.png" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" height="300" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjnIhK6HMtYRGJ_r-Cr1sIFZe36jJLXa5bHKEH3VREaYKpNeDTOli8wS4S_zgGIg5X63BUeLQVPv3AKlbN64e6x5LRcKKzLmO3P7YcF1RVmew0L4Cnvjlj1UIhOgvlwpsC7C7z_KhZc5CE/s400/Screenshot+from+2016-03-25+11%253A57%253A02.png" width="400" /></a></div>
<br />Here $\rho_X$ is the fraction of $B_s^0$ coming from tetraquark decays. Could there be some major difference in the production of $X$ or of $B^0_s$ in a $p\bar{p}$ (as in D0) versus a $pp$ (as in LHCb) collider? Would love to hear from an expert. In the mean time we wait for results from ATLAS/CMS, and in particular CDF (the partner experiment to D0 at Tevatron) to tell us more. There's a pop-sci article at Scientific American <a href="http://www.scientificamerican.com/article/new-tetraquark-particle-sparks-doubts/">here</a>.</li>
</ul>
<ul>
<li>LHC beam splashes tonight!</li>
</ul>
<ul>
<li>The CERN In Theory series continues: "Are theoreticians just <a href="http://home.cern/about/updates/2016/03/theory-are-theoreticians-just-football-fanatics">football fanatics</a>?" and "Why are theoreticians filled <a href="http://home.cern/about/updates/2016/03/theory-why-are-theoreticians-filled-wanderlust">with wanderlust</a>?"</li>
</ul>
<ul>
<li>Links without thinks:</li>
<ul>
<li>Physics World: Where people and particles collide: What’s it like to be in a <a href="http://physicsworld.com/cws/article/indepth/2016/mar/03/where-people-and-particles-collide">gender or sexual minority</a> at CERN, one of the most multicultural labs on the planet?</li>
<li>Nature: The <a href="http://www.nature.com/news/the-black-hole-collision-that-reshaped-physics-1.19612?WT.mc_id=TWT_NatureNews">black-hole collision</a> that reshaped physics</li>
</ul>
<li>In audio/video media:</li>
<ul>
<li>BBC News: Step inside the <a href="https://youtu.be/d_OeQxoKocU">Large Hadron Collider</a> (360 video). [3:14]</li>
<li>Q&A: <a href="http://www.abc.net.au/tv/qanda/txt/s4406559.htm">String Theory</a>, Sea Turtles, AI and Pi (featuring Brian Greene, Tamara Davis). [1:04:33]</li>
<li>Laura Baudis at Physics@FOM Veldhoven 2016: <a href="https://youtu.be/e4fk3PWk8-E">Dark Matter Detection</a> Masterclass. [2:09:54]</li>
<li>Johnny Depp and Lawrence Krauss: <a href="https://origins.asu.edu/depp-krauss-origins-project-dialogue">Origins Project</a> Dialogue. [~2hrs]</li>
</ul>
</ul>
Bluejayhttp://www.blogger.com/profile/06935684943024856641noreply@blogger.com0tag:blogger.com,1999:blog-959149188511266512.post-90588272561171127862016-03-06T15:38:00.000+11:002016-03-08T15:02:30.807+11:00Friday wrap-up: LIGO, chasing the 750 GeV excess...Apologies for the long hiatus -- other aspects of life have been getting in the way. Here is a summary of the last month or so...<br />
<br />
<ul>
<li>Of course the biggest news was the first observation of gravitational waves, a binary stellar-mass black hole system, and a binary black hole merger. Not bad for an <a href="http://journals.aps.org/prl/abstract/10.1103/PhysRevLett.116.061102">8 page paper</a>! The signal is really quite striking; it's wonderful to see the agreement between the two detectors. I reproduce the observation plot below, just because one cannot admire it enough.<br /><br /><div class="separator" style="clear: both; text-align: center;">
<a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgHbcRcQ8Ha8ujY2u_TGg7J4QZZzLSjNtIhmPozPczAtHU8bmaIszm5ONUuTL9QP_VihAg9xf3fO9Qi9dxsn0BVQrzCa5_625g77Rp6LERVyilQFrK-uI274UpqrRTWQQupL6n1cWlUz1U/s1600/Screenshot+from+2016-03-04+08%253A52%253A38.png" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" height="321" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgHbcRcQ8Ha8ujY2u_TGg7J4QZZzLSjNtIhmPozPczAtHU8bmaIszm5ONUuTL9QP_VihAg9xf3fO9Qi9dxsn0BVQrzCa5_625g77Rp6LERVyilQFrK-uI274UpqrRTWQQupL6n1cWlUz1U/s400/Screenshot+from+2016-03-04+08%253A52%253A38.png" width="400" /></a></div>
<div style="text-align: center;">
<br /></div>
Interest in the finding was phenomenal; the Physical Review Letters server even crashed (they were getting <a href="https://www.insidehighered.com/news/2016/02/24/how-ligo-and-physical-review-letters-worked-together-publish-paper-lifetime">10k hits</a> per minute). One can find plenty of explanations at various levels online: e.g. for the layperson see <a href="https://www.quantamagazine.org/20160211-gravitational-waves-discovered-at-long-last/">Quanta</a>, or Brian Greene on <a href="https://youtu.be/ajZojAwfEbs">the Late Show</a>; for the more scientifically minded there exists a <a href="http://cplberry.com/2016/02/23/gw150914-the-papers/">digestible summary</a> of each paper by Christopher Berry; or for a colloquium-level talk see <a href="https://cds.cern.ch/record/2131411">Barry Barish</a> at CERN. Lastly you can enjoy the <a href="http://xkcd.com/1642/">xkcd</a>.<br /><br />Here I just want to mention some interesting facts, taking as read the core ideas behind the phenomenon and the measurement. The event was actually observed before the first planned science run, during an engineering run. It was identified within 3 minutes and the decision was subsequently made to keep settings in place to take 16 more live days of data. This time period was chosen so that the data-driven background estimation could nail down the unlikeliness of the event to >5.1σ under the background-only hypothesis. Below is shown the event and background estimation; the detection is well in excess of 5.1σ, even including the event itself in the background estimation.<br /><br /><div style="text-align: center;">
<a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEghwvDquGEwktvBYsRTmZC3quLZSeNZzMMzb9bGEzJuQqAc9W-jnACBLq_OxVQFMf0mGJ57QZg-vBvrEhJzvvN0d3MBRqFJmO4f39LEZWAk23DsYUyDmLh-njY3UEsOmWIK410_O1Qqn3s/s1600/Screenshot+from+2016-03-04+09%253A15%253A41.png" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" height="303" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEghwvDquGEwktvBYsRTmZC3quLZSeNZzMMzb9bGEzJuQqAc9W-jnACBLq_OxVQFMf0mGJ57QZg-vBvrEhJzvvN0d3MBRqFJmO4f39LEZWAk23DsYUyDmLh-njY3UEsOmWIK410_O1Qqn3s/s400/Screenshot+from+2016-03-04+09%253A15%253A41.png" width="400" /></a></div>
<br />The <a href="https://losc.ligo.org/s/events/GW150914/GW150914_tutorial.html">data is in fact completely open</a> and you could analyse it yourself! In addition to the GW150914 event there are also two others that rise somewhat above the background ("GW151012" and "GW151226"). You can see them by eye in the above plot. They are clearly not statistically significant enough to announce a discovery alone, but still they are tantalising... <span style="text-align: center;">with room for improvement to design sensitivity (by a factor of ~2 which increases the spatial reach by 2^3) and the construction of a third detector in India to triangulate the signal, the future of gravitational wave astronomy is exciting.</span></li>
</ul>
<ul>
<li>There's also that puzzling <a href="http://arxiv.org/abs/1602.03920">observation by Fermi</a> of a gamma-ray burst 0.4s after the gravitational wave detection. There are good reasons for and against believing this was associated with the GW150914 event (see <a href="https://www.quantamagazine.org/20160302-black-hole-flash/">Quanta</a>); the best way to tell is to just to wait and see if it happens again!</li>
</ul>
<ul>
<li>On the 750 GeV diphoton excess you can read Jester's "<a href="http://resonaances.blogspot.com.au/2016/01/750-ways-to-leave-your-lover.html">750 ways</a> to leave your lover" on various explanations.<br /><br />As well, a <a href="http://arxiv.org/abs/1602.05581">comprehensive paper</a> appeared on the arXiv reviewing some of the renormalisable and weakly-coupled explanations. In the authors' literature review they "found a wide range of mistakes or unjustified assumptions, which represent the main motivation that prompted this work." The suggestion is to utilise computational tools (e.g. SARAH) to automate the work which the phenomenologist should be doing anyway for a thorough analysis, and they provide 40 model files to match models already in the literature.<br /><br />Let us review these "mistakes or unjustified assumptions"; we will refer to the resonant 750 GeV state as $S$ throughout, and consider models where the effective coupling of $S$ to the diphoton/digluon vertices are induced by a loop of gauge-charged fermion(s) or scalar(s) [of course there are explanations which do not fit into this framework]...<br /><br /><b>Next-to-leading-order (NLO) corrections</b> to the $S$ decay widths matter. Compared to the LO result used in many papers, NLO corrections typically decrease $\Gamma(S\to\gamma\gamma)$ by O(10%), and N3LO corrections can increase $\Gamma(S\to gg)$ by a factor of almost 2. Overall this means $Br(S\to gg)/Br(S\to\gamma\gamma)$ is typically underestimated (for scalar $S$) by as much as a factor of 2 when using the LO estimate. This will change best fit regions and lead to stronger constraints from the dijet channel. Models which live on the edge of exclusion based on LO estimations may not survive.<br /><br />It is often assumed <b>that $S$ does not mix</b> with the SM Higgs. But mixing is necessarily generated at some loop level. If a fermion is in the loop it is a three-loop effect (but with large Yukawas and strong gauge couplings at the vertices). If a scalar is in the loop it arises at one-loop. This contribution can be turned off by tuning a quartic term to zero [this is not stable under the renormalisation group evolution], but there is always a pure-gauge two-loop contribution. This effect should be acknowledged and checked for consistency.<br /><br />Another common assumption is that <b>the $S$ vev is zero</b>. But since there is a $Sgg$ vertex the $S\to -S$ symmetry must be broken when expanded around the vacuum ($S=S_0 - \langle S_0 \rangle$). It is hard to imagine a non-finely-tuned potential with this property and a minimum at $\langle S_0 \rangle=0$. Another way to argue this is made in the paper: if the original state $S_0$ couples at a three-point vertex with a new fermion or scalar, then a tadpole term will induce a non-zero linear $S_0$ contribution which acts like a vev insertion.<br /><br /><b>Decay channels have been missed</b> in some works which can significantly change conclusions.<br /><br />In the proposed models it is necessary to have a rather large diphoton width. The authors identify three main methods for achieving this. There are worries with each of them which have not been addressed uniformly in the literature....<br /><br />1. If fermion in the loop, then a <b>large Yukawa</b> coupling $yS\psi\bar{\psi}$. Typically these need to be O(1). Naturally, one should make sure perturbativity is under control when calculating the one-loop effective coupling. There exist papers which don't. As well, even if it remains pertubatively controlled at the 750 GeV scale, the renormalisation group evolution can evolve that Yukawa to the non-perturbative regime at some higher energy. This should be checked and at least acknowledged. [It is an interesting fact that this does not happen in the standard model for the top Yukawa; it is ~1 at the electroweak scale and shrinks with energy scale due to Higgs/top quark gauge contributions].<br /><br />2. If scalar in the loop, then a <b>large cubic term</b> $\kappa S XX$. The authors point out that this generally leads to problems with stability of the electroweak vacuum. I will also add that if the cubic term is large (>TeV) compared to the desired sub-TeV particles, then it is likely that the vacuum potential must be somewhat tuned, and this will not be stable under radiative corrections.<br /><br />3. Instead of relying on a large Yukawa or cubic, <b>increase the charge </b>coupling the loop fermion/scalar to gluons/photons or have <b>more particles</b> in the loop. Papers exist with Q≥5 and N=9000. However, such changes induce a large correction to the gauge coupling renormalisation group running above threshold, and can lead to high-energy electroweak behaviour which is ruled out, or worse to a Landau Pole at energies below 1 TeV.</li>
</ul>
<ul>
<li>My conclusion from all this: even if one does not object to the phenomena of ambulance chasing [I personally do not object to the principle], one should object to the lack of quality that seems to go along with it. It is a problem that assumptions are made and effects are overlooked which change conclusions considerably. It is a problem that lower quality papers are (at least for a good while) cited on par with better considered ones. It is a problem that we are mostly seeing the same idea embedded into different models with no qualitatively new observations. In addition, it is frustrating that (non-)participation in trending topics has implications for whether you can continue to make your way in the field, especially for early career researchers.</li>
</ul>
<ul>
<li>On a lighter note, see the arXiv preprint "A Theory of <a href="http://arxiv.org/abs/1603.01204">Ambulance Chasing</a>" by Mihailo Backović (a 750 GeV ambulance chaser himself!) for a bit of fun, where he attempts to model the total number of papers on a trending topic as a function of time. For the diphoton excess: "It follows that if the interest scales as an inverse power law in time, the cumulative number of papers on a topic is well described by a di-gamma function, with a distinct logarithmic behavior at large times." "Di-gamma" is just brilliant. A (testable) prediction of this model is that "the total number of papers will not exceed 310 by June 1, 2016". If you feel like you have a better model, then throw <a href="http://cp3.irmp.ucl.ac.be/~mbackovic/">your hat</a> into the ring! </li>
</ul>
<ul>
<li>The <a href="http://heppostdocproject.com/">HEP Postdoc Project</a> has appeared. To quote the website: "The HEP Postdoc Project intends to be a tool for Postdocs, or even PhD students, in the area of High Energy Physics... When an applicant accepts an offer, she/he is lacking, however, important information about the senior researchers in the corresponding institution... The goal of the HEP Postdoc Project is to fill this gap. Please, send us your opinions on senior high energy physicists you have interacted with in the past..."</li>
</ul>
<ul>
<li>CERN is doing an "In Theory" series of articles on the CERN Theory department. The <a href="http://home.cern/about/updates/2016/02/theory-welcome-theory-corridor">first</a>-<a href="http://home.cern/about/updates/2016/03/theory-why-bother-theoretical-physics">two</a> installments are "Welcome to the Theory corridor" and "why bother with theoretical physics?"</li>
</ul>
<ul>
<li>Conferences/workshops:</li>
<ul>
<li>CoEPP Annual Workshop 2016 (<a href="https://indico.cern.ch/event/484161/timetable/">indico</a>)</li>
<li>LHC Performance Workshop (<a href="https://indico.cern.ch/event/448109/other-view?view=standard">indico</a>)</li>
<li>UCLA Dark Matter 2016 (<a href="https://conferences.pa.ucla.edu/dm16/agenda.html">agenda</a>)</li>
<li>CERN Winter School on Supergravity, Strings, and Gauge Theory 2016 (<a href="https://indico.cern.ch/event/439879/timetable/#20160203">indico</a>)</li>
</ul>
</ul>
<ul>
<li>Links without thinks:</li>
<ul>
<li>Stories of Australian Science: Looking for <a href="http://stories.scienceinpublic.com.au/2015/darkmatter/">dark matter</a> in a gold mine.</li>
<li>Sabine Hossenfelder via aeon: The <a href="https://aeon.co/essays/is-dark-matter-subatomic-particles-a-superfluid-or-both">superfluid</a> Universe.</li>
<li>SciAm: Physicist <a href="http://blogs.scientificamerican.com/cross-check/physicist-sabine-hossenfelder-fears-theorists-lacking-data-may-succumb-to-wishful-thinking/">Sabine Hossenfelder</a> Fears Theorists, Lacking Data, May Succumb to "Wishful Thinking".</li>
<li>Smashpipe: Who's winning the string wars and why should you care? [<a href="https://smashpipe.com/article/639">Part 1</a> and <a href="https://smashpipe.com/article/651">Part 2</a>]</li>
<li>Quanta: From Einstein’s Theory to <a href="https://www.quantamagazine.org/20160218-gravitational-waves-kennefick-interview/">Gravity’s Chirp</a>.</li>
<li>Lawrence Krauss via New Yorker: Do the New, Big-Money <a href="http://www.newyorker.com/tech/elements/do-the-new-big-money-science-prizes-work?intcid=popular">Science Prizes</a> Work?</li>
<li>symmetry magazine: <a href="http://www.symmetrymagazine.org/article/the-abcs-of-particle-physics">The ABCs</a> of particle physics.</li>
</ul>
</ul>
<ul>
<li>In audio/video media:</li>
<ul>
<li>Recordings of <a href="https://videoonline.edu.lmu.de/en/wintersemester-2015-2016/7475">talks from</a> "Why Trust a Theory? Reconsidering Scientific Methodology in Light of Modern Physics" [In my opinion, more conferences/workshops should record and make public their talks like this].</li>
<li>CMS Experiment: An introduction to the <a href="https://youtu.be/S99d9BQmGB0">CMS Experiment</a> at CERN. [7:25]</li>
<li>Katherine Freese at Perimeter Institute: The <a href="https://youtu.be/Ma3nwq5ltZs">Dark Side</a> of the Universe. [1:03:16]</li>
<li>Gianfranco Bertone: The Quest for <a href="https://youtu.be/hSNlSJfIV90">Dark Matter</a>. [1:00:23]</li>
<li>Camilo Garcia-Cely: Phenomenology of <a href="https://youtu.be/Gt4XrHpQr-8">Left-Right Symmetric</a> Dark Matter. [1:06:30]</li>
<li>Gero von Gersdoff: Light by light scattering and the <a href="https://youtu.be/9ozy5akOL3A">750 GeV diphoton</a> excess. [58:00]</li>
<li>The Good Stuff: What the Heck is <a href="https://youtu.be/6XWIILSVdv4">Dark Matter</a>? [12:02]</li>
<li>Stephen Sekula SMU Godbey Lecture: "<a href="https://youtu.be/brcutT4k5e4">The Tail of</a> the Lion: 100 Years of General Relativity, the Scientific Theory of Space and Time" [1:10:05]</li>
<li>La physique autrement: Physics <a href="https://vimeo.com/145981138">and caffeine.</a> [9:12]</li>
</ul>
</ul>
Bluejayhttp://www.blogger.com/profile/06935684943024856641noreply@blogger.com1tag:blogger.com,1999:blog-959149188511266512.post-81422936230737391602016-01-29T22:22:00.000+11:002016-01-31T09:53:46.179+11:00Friday wrap-up: diphoton uncertainties, dark matter uncertainties...Wherein I list some (mostly) recent happenings, ramble a bit, and provide links, in an order roughly determined by importance and relevance to particle physics. Views are my own. Content very definitely skewed by my own leanings and by papers getting coverage, and it may not even be correct. It is a blog after all...<br />
<br />
<ul>
<li>There's quite a bit of discussion over <a href="http://resonaances.blogspot.com.au/2016/01/gunpowder-plot-foiled.html">at Résonaances</a> (see also the comments) surrounding the Davis-Fairbairn-Heal-Tunney <a href="http://arxiv.org/abs/1601.03153">paper</a> proposing an underestimated systematic in the background parameterisation used in the ATLAS diphoton analysis. This (and related) discussion looks to have aided (according to the acknowledgments) the preparation of <a href="http://arxiv.org/abs/1601.07330">another paper</a> from Bradley Kavanagh, which seems to clarify the issue. In that paper it is written:<br /><br /><i>Davis et al. introduce a different possible parametrisation for the background (which was also validated by a Monte Carlo study) and find that the significance of the excess is further reduced with respect to the k = 1, fixed-N case. However, the empty bins at high mγγ were not included in that analysis, leading to a background fit which overestimates the high mγγ event rate. Indeed, using the Davis et al. background parametrisation (with free normalisation) in this analysis gives a local significance of 3.8σ for a free-width resonance. This does not discount the possibility that exploring a wider range of possible background functions may impact the significance of the 750 GeV excess, but the correct constraints from the entire range of mγγ should be taken into account.</i></li>
</ul>
<ul>
<li>A <a href="http://arxiv.org/abs/1601.04707">few</a>-<a href="http://arxiv.org/abs/1601.04725">interesting</a>-<a href="http://arxiv.org/abs/1601.05402">papers</a> appeared concerning baryonic effects on the local dark matter velocity distribution, of interest for interpreting direct detection experiments (see Matthew Buckley's <a href="http://www.physicsmatt.com/blog/2016/1/20/paper-explainer-assessing-astrophysical-uncertainties-in-direct-detection-with-galaxy-simulations">blog</a> for a write-up of one of them). Each of the papers takes a number of simulated Milky Way-like galaxies and looks at the dark matter distribution at Solar radius. Naturally, due to the small number of simulated galaxies, the papers reach slightly different conclusions. What is clear, though, is that there are significant uncertainties in both the local density and the local velocity distribution, which means that the usual direct detection limits you see drawn on e.g. σSI versus mχ space should be taken with a small grain of salt, since they assume the standard halo model. Also of note is that these effects alone cannot ameliorate tension with the DAMA/CoGeNT events. Further work in this area will be interesting to follow as additional (and more detailed) simulations become available.</li>
</ul>
<ul>
</ul>
<ul>
<li>Links without thinks</li>
<ul>
<li>.Mic: "With <a href="http://mic.com/articles/132709/with-one-hashtag-female-astronomers-share-their-heartbreaking-stories-of-harassment">One Hashtag</a>, Female Astronomers Share Their Heartbreaking Stories of Harassment"</li>
<li>Nicolas Gisin via IQOQI: "<a href="http://www.iqoqi-vienna.at/nicolas-gisin/">Thought police</a> – on arXiv?"</li>
<li>BackReaction: "Does the <a href="http://backreaction.blogspot.com.au/2016/01/does-arxiv-censor-submissions.html">arXiv censor</a> submissions?"</li>
<li>nature: "Hawking’s latest black-hole paper <a href="http://www.nature.com/news/hawking-s-latest-black-hole-paper-splits-physicists-1.19236">splits physicists</a>"</li>
<li>Ars Technica: "The search for dark matter <a href="http://arstechnica.com/science/2016/01/the-search-for-dark-matter-heats-up/">heats up</a>"</li>
</ul>
</ul>
<ul>
<li>In audio/video media:</li>
<ul>
<li>IQIM Caltech: <a href="https://youtu.be/Hi0BzqV_b44">Anyone Can Quantum</a>, a quantum chess match between Paul Rudd and Stephen Hawking. [11:50]</li>
<li>CERN: CERN's new <a href="https://youtu.be/ZB0vnP7uuko">microcosm exhibition</a> is now open. [0:41]</li>
<li>Fermilab: <a href="https://youtu.be/FBeALt3rxEA">Quantum Field Theory</a>. [5:29]</li>
<li>Fermilab: Why I Love <a href="https://youtu.be/LEyVsGGqsVg">Neutrinos</a> - Professor Naba Mondal. [0:59]</li>
</ul>
</ul>
<ul>
<li>A sad day for Comic Sans enthusiasts everywhere (nowhere?) -- apparently no more from Fabiola...<br /><br /><blockquote class="twitter-tweet" lang="en">
<div dir="ltr" lang="en">
Historical moment announced at <a href="https://twitter.com/CERN">@CERN</a> during DG Fabiola Gianotti's new year address: The End of the <a href="https://twitter.com/hashtag/ComicSans?src=hash">#ComicSans</a> Era! <a href="https://t.co/nhw6TabNbZ">pic.twitter.com/nhw6TabNbZ</a></div>
— Steven Goldfarb (@stevengoldfarb) <a href="https://twitter.com/stevengoldfarb/status/689044046661185536">January 18, 2016</a></blockquote>
<script async="" charset="utf-8" src="//platform.twitter.com/widgets.js"></script></li>
</ul>
Bluejayhttp://www.blogger.com/profile/06935684943024856641noreply@blogger.com0tag:blogger.com,1999:blog-959149188511266512.post-31359186610305642542016-01-15T22:10:00.002+11:002016-02-11T12:49:22.568+11:00Friday wrap-up: gravitational* waves?...A short list this week. And the next post will be in two weeks...<br />
<br />
<ul>
<li><a href="https://twitter.com/LKrauss1/status/686574829542092800">Strong</a>-<a href="http://www.theguardian.com/science/2016/jan/12/gravitation-waves-signal-rumoured-science">rumours</a>-<a href="http://www.nature.com/news/gravitational-wave-rumours-in-overdrive-1.19161">circulating</a> about a potential LIGO discovery of gravitational waves from merging black holes.</li>
</ul>
<ul>
<li>The 6th International Workshop on High Energy Physics in the LHC Era was on from 6-12th Jan [<a href="http://indico.cern.ch/event/385771/timetable/#20160106.detailed">indico</a>].</li>
</ul>
<ul>
<li>Links without thinks</li>
<ul>
<li>Scientific American: "Stephen Hawking's New <a href="http://blogs.scientificamerican.com/dark-star-diaries/stephen-hawking-s-new-black-hole-paper-translated-an-interview-with-co-author-andrew-strominger/">Black-Hole Paper</a>, Translated: An Interview with Co-Author Andrew Strominger"</li>
<li>Sabine Hossenfelder via Quanta: "String Theory <a href="https://www.quantamagazine.org/20160112-string-theory-meets-loop-quantum-gravity/">Meets</a> Loop Quantum Gravity"</li>
<li>Nautilus: "<a href="http://nautil.us/issue/32/space/beauty-is-physics-secret-weapon">Beauty</a> Is Physics’ Secret Weapon," an interview with Frank Wilczek.</li>
</ul>
</ul>
<ul>
<li>In audio/video media:</li>
<ul>
<li>Hitler doesn't get <a href="https://youtu.be/VjgmcZwaY1Y">a postdoc</a> in High Energy Theory. [3:49]</li>
<li>NASA: <a href="https://youtu.be/G0dOoqelczY">Fermi Sharpens</a> its High-Energy View. [5:30]</li>
<li>Sixty Symbols: <a href="https://youtu.be/I55e6chHUs0">Hairy Black Holes</a> and Super Selfies. [7:11]</li>
<li>Physics Girl: 5 <a href="https://youtu.be/xyXpQxz7BOs">amazing stars</a> we’ve discovered in space. [7:00]</li>
<li>SpaceX: "The Falcon has landed" Recap of <a href="https://youtu.be/ANv5UfZsvZQ">Falcon 9</a> launch and landing. [3:37]</li>
</ul>
</ul>
<ul>
<li>The collaborative diphoton project mentioned in the previous two posts is gaining some momentum. Watch this space...</li>
</ul>
Bluejayhttp://www.blogger.com/profile/06935684943024856641noreply@blogger.com0tag:blogger.com,1999:blog-959149188511266512.post-41004565210501469102016-01-09T17:29:00.002+11:002016-01-09T23:30:06.728+11:00Friday wrap-up: diphoton, self-interacting dark matter direct detection...Back from the end of year break and getting stuck into new projects! Here is the first Friday wrap-up of 2016...<br />
<div class="separator" style="clear: both; text-align: center;">
<br /></div>
<ul>
<li>Fabiola Gianotti <a href="http://press.web.cern.ch/press-releases/2015/12/cern-director-general-rolf-heuer-passes-baton-fabiola-gianotti">is now</a> CERN's Director-General.</li>
</ul>
<ul>
<li>The 750 GeV diphoton monsoon which hit the arXiv on 16th December has <a href="http://jsfiddle.net/adavid/bk2tmc2m/show/">not yet abated</a>. There are 150-odd papers now up on the arXiv. See ReSonaances <a href="http://resonaances.blogspot.com.au/2015/12/750-and-what-next.html">here</a> and <a href="http://resonaances.blogspot.com.au/2016/01/do-or-die-year.html">here</a>, <a href="http://www.science20.com/a_quantum_diaries_survivor/the_750_gev_diphoton_bump_what_it_cannot_be-162715">Tommaso Dorigo</a>, and recent posts on <a href="http://motls.blogspot.com/">the reference frame</a>.<br /><br />I personally think that it is a good exercise for the hep-ph community to ask the question, <i>if it is real, then what could it be?</i> At least for the scientifically motivated reason that extra predictions are generally made which might be tested, and these predictions could in principle serve as a guide to tell experimentalists where to probe nature next (in the case that this turns out to be real). It is also sensible to collectively gather ideas which might help to fit the thing into a bigger picture. Unfortunately these good scientific motivations are confounded by citation-chasing, repetition, ill-motivated "Hail Mary" models, repetition, repetition, etc. We must also be aware of our (unscientific) cognitive bias toward fluctuations from the mean: given the statistical significance of the signal, is all this work sufficiently scientifically motivated? This is an interesting question, if rather academic... it is naive to think that scientists are (or even should be) motivated by purely scientific considerations.<br /><br />Anyway, the time should come for we as a community to sit back and take stock. The problem then is, among the noise, how to reduce the growing theory-space to a set of distinct generic predictions. I am considering pursuing this in the form of a wiki (or similar) as an experiment in large-scale collaboration; the idea would be to produce a summary document which represents a balanced cross-section of hep-ph ideas on this thing (with no cap on author count). The difficulties include the administrative one of keeping such a project economic and efficient, but also keeping a fair balance and controlling the (possibly inevitable) politics involved. <b>If you have ideas or would like to get involved in such a project, please leave a comment or send me an email</b>, so that I may gauge the interest in such a thing...<br /><br />There is not too much more to say except that there are myriad explanations for this possible signal, and I think it is sensible to be ready if it does turn out to be real. That being said, it would take a brave person to claim that the odds are in its favour...</li>
</ul>
<ul>
<li>Before Christmas we finished up on a fun project: "Plasma dark matter <a href="http://arxiv.org/abs/1512.06471">direct detection</a>." The paper concerns what is a rather under-appreciated and somewhat generic point about self-interacting dark matter models and direct detection experiments. The logic goes like this:<br /><br /><b>(1) </b>If dark matter is self-interacting and capable of giving a direct detection signal, then some amount will be captured within the Earth. <b>(2) </b>The annually varying dark matter wind will interact with this captured dark matter in a highly non-trivial way. <b>(3)</b> This will result in a complex space- and time-varying dark matter near-Earth environment. <b>(4)</b> The dark matter detector moves through this environment throughout the day/year, and the rate it measures will be a time-average of the local rate along its path through space.<br /><br />In the well studied WIMP dark matter scenario, there is no spatial dependence of the dark matter distribution near the Earth, and so it doesn't matter where your detector is in space. Our scenario is quite different. Both the dark matter wind speed and the detector's daily path annually modulate due to the Earth's motion around the Sun. These modulations have different phases (155 days vs 115 days). So now you have two sources of annual modulation which, due to the complex dark matter environment, give an annually modulating rate which does not necessarily resemble a sinusoid. The following animations should help to visualise this picture:<br /><br /><div class="separator" style="clear: both; text-align: center;">
<a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEiV3Tnjzg7IyfoVdjk8Ynfolb8JXUMY61foPANELcZJIldfum_L_AkxYpIdh7eu-eq2JSlqcYSoR_G5vyEkeaGViQcXCvbmHNlWplc2vrsmnHtV3msrPOOVmuwGpReOLwH1F-Yl2hzJNWQ/s1600/Moon240.gif" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" height="216" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEiV3Tnjzg7IyfoVdjk8Ynfolb8JXUMY61foPANELcZJIldfum_L_AkxYpIdh7eu-eq2JSlqcYSoR_G5vyEkeaGViQcXCvbmHNlWplc2vrsmnHtV3msrPOOVmuwGpReOLwH1F-Yl2hzJNWQ/s400/Moon240.gif" width="400" /></a></div>
<div class="separator" style="clear: both; text-align: center;">
<a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhcObQZk3y1Rkq6pKj7mwlZIOOXe20NkYngAx29scu41QpbB633_11pqQKyT9TK5lZEcUL7sl2C-dGBk6ym5MM4lMFb82T6y-26EvkphOUwDRoH-VeRMhisxMXiMxxhfVvFnzercVgF8Oc/s1600/Venus200.gif" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" height="216" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhcObQZk3y1Rkq6pKj7mwlZIOOXe20NkYngAx29scu41QpbB633_11pqQKyT9TK5lZEcUL7sl2C-dGBk6ym5MM4lMFb82T6y-26EvkphOUwDRoH-VeRMhisxMXiMxxhfVvFnzercVgF8Oc/s400/Venus200.gif" width="400" /></a></div>
<br />These are two simplified captured dark matter scenarios (fully absorbing/reflective) which we considered. The dark matter wind comes in from the left and its speed annually modulates. The direction of the Earth's rotation axis with respect to the wind also annually modulates, and therefore so do the detectors' daily paths: the black, green, orange, red bars represent the location of detectors in Gran Sasso, Kamioka, China Jin-Ping, and Stawell, respectively. Clearly, due to the complex environment, they will measure very different things! This is the qualitative picture; to make quantitative predictions is very difficult. This is why multiple experiments at multiple latitudes will be important for probing this scenario, especially experiments in the Southern Hemisphere (such as Stawell) which inhabit a unique location behind the Earth with respect to the wind.<br /><br />Lastly, the generic and distinctive prediction of these models is a possibly strong and non-trivial modulation as a function of time of sidereal day (diurnal modulation). A <a href="https://en.wikipedia.org/wiki/Sidereal_time">sidereal day</a> is an "astronomical day" slightly shorter than a 24 hour day; there are approximately 366 sidereal days in a year. It is hard to imagine any background process which would modulate with period of one sidereal day. It therefore seems like a very sensible dark matter search to perform in addition to an annual modulation search.<br /></li>
<li>Already in a <a href="http://syymmetries.blogspot.com.au/search/label/XMASS">few previous posts</a> I mentioned the recent XMASS annual modulation search and its possible hint of a modulation signal with opposite sign to that of DAMA. Out of interest, last week I got around to scraping their central values from the data in the backup slides of their <a href="http://www.taup-conference.to.infn.it/2015/day2/parallel/dma/3_kobayashi.pdf">TAUP talk [pdf]</a>. Below I present their measurement of rate as a function of time for energy bins summed from 0.5--2.0 keV57Co.<br /><br /><div style="text-align: center;">
<a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgKvOw3LNKKkrzlZR1tvX3VVOq0T6Nc-M-3XJSv7e05tCaY5AKm0X-qUw4dB-nyaqJM4a79jbBCQCvglLlGP0i3XC-pXMHqALVc3YPdZtnV_WY2bl6Ab0DjWM-r4l9Q18nlabCw3OIrjYo/s1600/0656c420-89d5-47cd-980d-8d0195c6b50c.png" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" height="296" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgKvOw3LNKKkrzlZR1tvX3VVOq0T6Nc-M-3XJSv7e05tCaY5AKm0X-qUw4dB-nyaqJM4a79jbBCQCvglLlGP0i3XC-pXMHqALVc3YPdZtnV_WY2bl6Ab0DjWM-r4l9Q18nlabCw3OIrjYo/s400/0656c420-89d5-47cd-980d-8d0195c6b50c.png" width="400" /></a><br />
<br />
<div style="text-align: left;">
The error bars are statistical only (though they dominate the systematic error) and have been estimated assuming equally spaced bins (which is not exactly correct); these errors are therefore only there to guide the eye and the actual ones would be if anything slightly larger. For interest the sinusoid of best fit, with a phase of 129 (or 311) days, is also plotted.<br />
<br />
Their result is clearly intriguing. It looks convincing to me, though one would need another year of data to tell for sure, and it will be interesting to see whether this effect continues in their fiducial volume (this analysis is full volume). What's going on here? It is consistent with a seasonal effect, but with amplitude opposite to that of DAMA. Though possible, if the modulation is due to an environmental effect then at least qualitatively this seems strange, since each of XMASS/DAMA are in the Northern Hemisphere (XMASS at Kamioka 36°N, DAMA at 43°N). The results of the annual modulation experiments sure are puzzling: there are four published now each seeing an effect at some level (though apart from DAMA are statistically weak)...<br />
<br />
Time might tell, but a speculative observation: if the XMASS effect is due to a non-trivial dark matter distribution, then the small change in latitude suggests that their signal will almost certainly be accompanied by large diurnal variation. So if XMASS see annual modulation in their fiducial volume, I would be very interested to see their search for a diurnal signal.</div>
</div>
</li>
</ul>
<ul>
<li>The XXII The Cracow Epiphany Conference on Run II LHC Physics (<a href="https://indico.ifj.edu.pl/indico/conferenceOtherViews.py?view=standard&confId=124#20160107">indico</a>) is currently on.</li>
</ul>
<ul>
<li>Links without thinks:</li>
<ul>
<li>The Hawking/Perry/Strominger Black Hole information loss problem paper <a href="http://arxiv.org/abs/1601.00921">hit the arXiv</a>; see <a href="http://backreaction.blogspot.com.au/2016/01/more-information-emerges-about-new.html">BackReaction</a> for more.</li>
<li>nature: "CERN’s <a href="http://www.nature.com/news/cern-s-next-director-general-on-the-lhc-and-her-hopes-for-international-particle-physics-1.19040">next director-general</a> on the LHC and her hopes for international particle physics"</li>
<li>nature: "Hint of new boson at LHC <a href="http://www.nature.com/news/hint-of-new-boson-at-lhc-sparks-flood-of-papers-1.19098">sparks flood</a> of papers"</li>
<li>nature: "Open journals that <a href="http://www.nature.com/news/open-journals-that-piggyback-on-arxiv-gather-momentum-1.19102">piggyback on arXiv</a> gather momentum"</li>
<li>Frank Wilczek via Quanta: "Time's <a href="https://www.quantamagazine.org/20160107-arrow-of-time-axions/">(Almost) Reversible</a> Arrow"</li>
<li>JSTOR: "An <a href="http://daily.jstor.org/i-heart-physics-love-story/">Amateur Critique</a> of String Theory"</li>
<li>Lee Smolin via Perimeter Institute: "<a href="http://www.perimeterinstitute.ca/einstein-storyteller">Einstein, Storyteller</a>"</li>
</ul>
</ul>
<ul>
<li>In audio/video media:</li>
<ul>
<li>In Particular: Things That <a href="https://inparticular.web.cern.ch/content/ep-4-things-go-bump-light">Go Bump</a> In The Light, on the diphoton excess. [21:47]</li>
<li>omega tau: <a href="http://omegataupodcast.net/2015/12/191-string-theory/">String Theory</a>. [2:43:07]</li>
<li>CBC radio: <a href="http://www.cbc.ca/radio/ideas/similes-and-science-part-1-1.3220861">Similes and Science</a>, on the Big Bang, string theory, black holes. [53:58]</li>
</ul>
</ul>
<ul>
<li>Lastly, in case you missed it, <a href="http://xkcd.com/1621/">the fixion</a>:<br /><br /><div class="separator" style="clear: both; text-align: center;">
<a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEi7pLOxuOdBoiKLjmDUdUgx2VRrtpFv3hVdz0mOjR6Glh8LYtyiaslvh1yVaerEx6kch50wQi4k8Mdwp9h4LL1cL6IMqS6_szsxrxRg1gfsASRVAOLQzS_TuLYDlP1Qn5b67yi5Ck8jB6o/s1600/fixion.png" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" height="326" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEi7pLOxuOdBoiKLjmDUdUgx2VRrtpFv3hVdz0mOjR6Glh8LYtyiaslvh1yVaerEx6kch50wQi4k8Mdwp9h4LL1cL6IMqS6_szsxrxRg1gfsASRVAOLQzS_TuLYDlP1Qn5b67yi5Ck8jB6o/s400/fixion.png" width="400" /></a></div>
<div style="text-align: center;">
<br /></div>
</li>
</ul>
Bluejayhttp://www.blogger.com/profile/06935684943024856641noreply@blogger.com1tag:blogger.com,1999:blog-959149188511266512.post-77620618301955925602015-12-20T09:18:00.001+11:002015-12-20T17:24:07.837+11:00Friday wrap-up: diphoton excess, no diboson, no gluinos...What a week! We have already seen some 40-odd papers submitted to hep-ph in the last few days on the "recent observed diphoton resonance" <b>[1]</b>. Well I certainly wouldn't go that far but ATLAS and CMS <i>have</i> each seen an excess of events in the diphoton spectrum at around 750 GeV, which is amazing since apparently they weren't even searching for it <b>[2]</b>, and anyway beside the point because they also discovered a gluino <b>[3]</b>. Sloppy science writing aside, what do we know?...<br />
<br />
<ul>
<li>The CMS and ATLAS Run II physics results presentations can <a href="https://indico.cern.ch/event/442432/">be found here</a>. Of course, all results presented are preliminary. The result that has hep-ph buzzing, though, is a little bump atop the falling diphoton invariant mass background (conference notes <a href="https://cds.cern.ch/record/2114808">here</a> and <a href="https://atlas.web.cern.ch/Atlas/GROUPS/PHYSICS/CONFNOTES/ATLAS-CONF-2015-081/">here</a>). [See <a href="http://resonaances.blogspot.com.au/2015/12/a-new-boson-at-750-gev.html">Jester</a>, <a href="http://motls.blogspot.com.au/2015/12/a-new-750-gev-boson-is-very-likely-there.html">Motl</a>, Strassler (<a href="http://profmattstrassler.com/2015/12/16/is-this-the-beginning-of-the-end-of-the-standard-model/">here</a> and <a href="http://profmattstrassler.com/2015/12/18/so-what-is-it/">here</a>), <a href="http://www.physicsmatt.com/blog/2015/12/16/diphotons-at-750-gev">PhysicsMatt</a>, or <a href="http://www.science20.com/a_quantum_diaries_survivor/knockin_on_new_physics_door-162273">Eilam Gross</a> for some physicist perspectives. Else in popular media I thought the <a href="http://www.nytimes.com/2015/12/16/science/physicists-in-europe-find-tantalizing-hints-of-a-mysterious-new-particle.html">NY Times article</a> was fairly balanced, but then I am a phenomenologist]. You can eyeball the bumps in question below (credit to <a href="http://profmattstrassler.com/2015/12/16/is-this-the-beginning-of-the-end-of-the-standard-model/">Strassler</a> for this image):<br /><br /><div style="text-align: center;">
<a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEho82JXBfSQti4B7IjftCr7NntRWBejxiLRX2Cvy5INAXpWFmE38Yjtyezz-6VQLmpVhST_TAeYDkrj817GA4ZwX79oO4Cap8HOm0vCvn-gGq9aKon_Ph3Mj9NTarlm1rwVNOTWu7maGLg/s1600/atlas_cms_diphoton_2015.png" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" height="400" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEho82JXBfSQti4B7IjftCr7NntRWBejxiLRX2Cvy5INAXpWFmE38Yjtyezz-6VQLmpVhST_TAeYDkrj817GA4ZwX79oO4Cap8HOm0vCvn-gGq9aKon_Ph3Mj9NTarlm1rwVNOTWu7maGLg/s400/atlas_cms_diphoton_2015.png" width="380" /></a></div>
<br />But what about the numbers? The <a href="http://syymmetries.blogspot.com.au/2015/12/friday-wrap-up-diphoton-excess.html">rumours</a> were as accurate as one could reasonably ask: assuming a narrow width resonance, CMS observed a <b>2.6σ local (1.2σ global)</b> excess at <b>760 GeV</b> [increases to 3.0σ local (1.7σ global) at 750 GeV when combined with the 8 TeV data], and; ATLAS observed <b>3.6σ local (2.0σ global)</b> at <b>750 GeV</b> [have not yet combined with 8 TeV, but if they did it appears the significance would fall]. Allowing the width to float to larger values, the CMS result goes down to 2.0σ local, whereas ATLAS observes a best fit 45 GeV (6%) width at 3.9σ local (2.3σ with multivariate look-elsewhere). The relevant slides are below:<br /><br /><div style="text-align: center;">
<a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjvPAWe6fT2olelw9afKp2drc-F4lySrwXExk_ar2Vuuh6rLNusO4b-19Rzsja5H8tyolFxur_negohtz-daemSiBwLPPI1OygWLT6VWKK8PkRaEAbWmAOexQh2inAUGNn_ZlpETDjYlck/s1600/Screenshot+from+2015-12-18+18%253A49%253A42.png" imageanchor="1" style="margin-left: 1em; margin-right: 1em; text-align: center;"><img border="0" height="300" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjvPAWe6fT2olelw9afKp2drc-F4lySrwXExk_ar2Vuuh6rLNusO4b-19Rzsja5H8tyolFxur_negohtz-daemSiBwLPPI1OygWLT6VWKK8PkRaEAbWmAOexQh2inAUGNn_ZlpETDjYlck/s400/Screenshot+from+2015-12-18+18%253A49%253A42.png" width="400" /></a></div>
<div style="text-align: center;">
<a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEiqO5o01NqvNIHDRkgHrqxRFULSheaSLNNJmNKk1F2rITO9bzAE8Uc6jCzkcGMe7yfjOWtn8F_occ80xBwIuZjuWL4e3ph7skBgYacb-gvpV9abjjINjA-KXl4Z8SmRg4_QNwOZ_i84Vl8/s1600/Screenshot+from+2015-12-18+18%253A41%253A35.png" imageanchor="1" style="margin-left: 1em; margin-right: 1em; text-align: center;"><img border="0" height="300" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEiqO5o01NqvNIHDRkgHrqxRFULSheaSLNNJmNKk1F2rITO9bzAE8Uc6jCzkcGMe7yfjOWtn8F_occ80xBwIuZjuWL4e3ph7skBgYacb-gvpV9abjjINjA-KXl4Z8SmRg4_QNwOZ_i84Vl8/s400/Screenshot+from+2015-12-18+18%253A41%253A35.png" width="400" /></a></div>
<br />It is a tantalizing excess. Sensibly, what one would like to know is the global significance of the fully combined (CMS+ATLAS 8+13 TeV) datasets. It is non-trivial to get an exact number (see <a href="https://indico.cern.ch/event/233551/contribution/1/attachments/389867/542286/cousins_look_elsewhere_14feb2013.pdf">here</a> or <a href="https://github.com/cranmer/look-elsewhere-2d/blob/master/two-experiment-lee.ipynb">here</a>), but one can at least make a good bet that it's greater than about $\sim \sqrt{1.7^2+2.0^2}\approx 2.6\sigma$, perhaps in the vicinity of $\sim 3\sigma$. [I would imagine the demand for a joint analysis is high enough to be a priority for the collaborations (or they might try to avoid feeding the hep-ph sharks?), so maybe we will have that number by <a href="http://moriond.in2p3.fr/">Moriond</a>]. This being a (very rough!) ~1/300 chance then, and given the hundreds of plots CMS and ATLAS produce, it is very possible that this is just a statistical fluctuation. Nonetheless, this excess is being taken fairly seriously, and will be exercising our scrolling finger on hep-ph for the foreseeable future while we grapple with the sensible question: <i>if it is real, then what could it be and what does it imply?</i> The answer to this question may have implications for the experimental program of the LHC over the next few years (at least), and so phenomenologists are already relentlessly hard at work...<br /><br />So let's try to answer that question: what could it be? Well, there is no evidence for any extra activity in the excess events, so it appears consistent with a simple $gg\to X\to \gamma\gamma$ resonance. If taken as a resonance, the events translate to a cross-section $\sigma(pp\to X)\times Br(X\to \gamma\gamma)$ of $\sim 2$/fb ($\sim 6$/fb) in the narrow (wide) width scenario. Let us try to build a model with these properties. The simplest thing is to add a scalar singlet to the standard model. To couple it to gluons and photons let's borrow the Higgs' trick and couple it to some coloured/charged fermion(s) which then induce the couplings via a loop. Let's try Yukawa coupling it to a vector-like up-type quark first, write down the effective couplings, and calculate the Yukawa necessary; we find that it has to be huge ($\sim 5$ or so). And there's a potential problem, since the singlet will want to decay most of the time to the up-type quark. That's okay! We will just make it heavy enough (> 375 GeV) so that it's not allowed. Now we're done, and this solution is "already well-known" <b>[4]</b>. We can add more vector-like fermions to quell the large Yukawa(s) somewhat and/or dial the $gg$ and $\gamma\gamma$ couplings independently. If we take the large width seriously, we still have to add extra decay channels, and then dial up the production and/or branching to photons to compensate. The obvious options are a dark sector or some other standard model states, which we have to hide from previous searches. We could also try constraining ourselves inside some more predictive (restrictive) model.<br /><br />Of course there are several papers on just the above, the implication being that <i>you need more than just the singlet scalar</i>, which is obviously quite interesting. The immediate implications for the LHC are: look for anything at 750 GeV in $jj, Z\gamma, ZZ$ (in roughly descending order of promise) as soon as is possible.<br /><br />But this is just a minimal model. It could also be a scalar/pseudoscalar/bound state connected to compositeness/extended gauge group/extra dimensions/hidden valley/SUSY/dark matter/naturalness, and you can be sure there are already arXiv submissions on all of these. On that, it seems to me that arXiv isn't quite the ideal platform for all this. It would be nice instead to have all the various proposals in the same place, with the same formatting, in no-nonsense form, all grouped by some general properties. Then the interested phenomenologist/experimentalist could go and browse a list of, for example: (1) candidate; (2) production; (3) couplings; (4) decays; (5) associated activity; (6) additional particles; (7) additional predictions. Of course this will inevitably be done anyway by some authors in a review, but it seems like the same could be achieved much more efficiently with a community-run wiki or similar, as long as there were some moderators willing to dedicate their time to such a project... any thoughts on this from readers?<br /><br />In my book there's not much more to say except <b>we need more data</b>, to tell (1) if this is real, or (2) what it is. Looking forward to more excellent work from our experimental colleagues in the new year.<br /><div style="text-align: center;">
<br /></div>
</li>
<li>Now onto other matters from the presentation. First the <a href="http://syymmetries.blogspot.com.au/2015/07/friday-wrap-up-diboson-excess-eps-hep.html">diboson excess</a> from Run I. Before the meeting a couple of useful papers appeared on the arXiv: a third-party CMS+ATLAS <a href="http://arxiv.org/abs/1512.03371">statistical combination</a>, and; a <a href="http://arxiv.org/abs/1512.04357">thorough summary</a> and literature survey. Now we know both CMS and ATLAS see nothing significant in Run II data (although they do not have sensitivity to conclusively probe the parameter space of interest):<br /><br /><div style="text-align: center;">
<a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhcszSIOW_OZ916BKicI2RPqtHvJnTP4HsGQvwW8mT2hHRfr89K5l7zPkB58PyT0KJrwnkauEOLhv6aj9I-lOxKNH7btKpZ1QLm3StvsFQbpnLkM2Sv_Papr7Elnn389UCObENP_mSDoD0/s1600/Screenshot+from+2015-12-18+18%253A44%253A30.png" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" height="300" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhcszSIOW_OZ916BKicI2RPqtHvJnTP4HsGQvwW8mT2hHRfr89K5l7zPkB58PyT0KJrwnkauEOLhv6aj9I-lOxKNH7btKpZ1QLm3StvsFQbpnLkM2Sv_Papr7Elnn389UCObENP_mSDoD0/s400/Screenshot+from+2015-12-18+18%253A44%253A30.png" width="400" /></a></div>
<div style="text-align: center;">
<a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjbEaY39TAahXQ1j_yK_Wcz326pOFRosOKenMxMF6dhxGLD6Idthc-KKDXqUiXuS8vtP_Ji6eZBgThDqabuoGDirwQEXe0Ym5J-QyY4IRkr1uA1RG2Ta3SdcJgEU3N_8s5Rv9uuVgQXYgM/s1600/Screenshot+from+2015-12-18+18%253A39%253A34.png" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" height="281" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjbEaY39TAahXQ1j_yK_Wcz326pOFRosOKenMxMF6dhxGLD6Idthc-KKDXqUiXuS8vtP_Ji6eZBgThDqabuoGDirwQEXe0Ym5J-QyY4IRkr1uA1RG2Ta3SdcJgEU3N_8s5Rv9uuVgQXYgM/s400/Screenshot+from+2015-12-18+18%253A39%253A34.png" width="400" /></a></div>
</li>
</ul>
<ul>
<li>Also in Run II data, the <a href="http://syymmetries.blogspot.com.au/2015/03/friday-wrap-up-atlas-on-z-excess-cms.html">on-Z</a> excess is not seen by CMS, but still persists at ATLAS...<br /><br /><div style="text-align: center;">
<a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjHy9L9YYMQRyEcbw80Wwap1RrE5AWQUpHVeS0LI2muWC_D0lkop2qC937HHgO65tZbEY86dMr8vEWGDn489mUpQy7_OTvhozRrpcGTIqZReopag4C80kCrqEFE16FZ3GBXdKiBsek7b94/s1600/Screenshot+from+2015-12-18+19%253A09%253A45.png" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" height="298" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjHy9L9YYMQRyEcbw80Wwap1RrE5AWQUpHVeS0LI2muWC_D0lkop2qC937HHgO65tZbEY86dMr8vEWGDn489mUpQy7_OTvhozRrpcGTIqZReopag4C80kCrqEFE16FZ3GBXdKiBsek7b94/s400/Screenshot+from+2015-12-18+19%253A09%253A45.png" width="400" /></a></div>
</li>
</ul>
<ul>
<li>As well, lots of gluino searches in different final states but nothing seen, and limits improve to roughly 1.2--1.8 TeV in the simplified models considered (but of course there are always compressed places to hide!).</li>
</ul>
<ul>
<li>CMS have not unblinded any of their Higgs analyses, but ATLAS reported results in γγ and ZZ: they were expecting 3.4σ observation and saw instead 1.4σ. Obviously the Higgs has packed up, moved to 750 GeV, and remembered its earlier proclivity for photons (this hypothesis will be robustly tested in upcoming LHC analyses).</li>
</ul>
<ul>
<li>Moving on to other news, LUX <a href="http://arxiv.org/abs/1512.03506">has released</a> new limits on spin-independent dark matter nucleon scattering. See the <a href="http://www.interactions.org/cms/?pid=1035364">press release</a> and/or <a href="http://www.quantumdiaries.org/2015/12/14/new-lux-results-on-wimp-nucleon-scattering/">this blog post</a> from Sally Shaw for a summary. They're almost observing solar neutrinos!<br /><br /><div class="separator" style="clear: both; text-align: center;">
<a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEiITXPya6hAT4AlSt0dRcyRvGwLpHcYnaknt1LkNww3uKo6RiAzQuMBGNQe9hNAZXE7sQkeh4ll8dnQYOK1NFkrorrUEKxCpKyK1-Ox8mX_pVNI8hxu_mc3BtaZzr89QKHAzcqUzuDpHvA/s1600/Screenshot+from+2015-12-20+08%253A33%253A41.png" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" height="400" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEiITXPya6hAT4AlSt0dRcyRvGwLpHcYnaknt1LkNww3uKo6RiAzQuMBGNQe9hNAZXE7sQkeh4ll8dnQYOK1NFkrorrUEKxCpKyK1-Ox8mX_pVNI8hxu_mc3BtaZzr89QKHAzcqUzuDpHvA/s400/Screenshot+from+2015-12-20+08%253A33%253A41.png" width="355" /></a></div>
</li>
</ul>
<ul>
<li>"NuPhys2015: Prospects in Neutrino Physics" was on this week (<a href="https://indico.ph.qmul.ac.uk/indico/conferenceTimeTable.py?confId=48">indico</a>).</li>
</ul>
<ul>
<li>Winners of the 2015 InterActions Physics Photowalk <a href="http://www.interactions.org/cms/?pid=1035363">were announced</a>.</li>
</ul>
<ul>
<li>Links without thinks:</li>
<ul>
<li>Strumia's <a href="http://astrumia.web.cern.ch/astrumia/InstantPaper.html">insta-paper</a> archive.</li>
<li>Quanta: "A Fight For the <a href="https://www.quantamagazine.org/20151216-physicists-and-philosophers-debate-the-boundaries-of-science/">Soul of Science</a>," on the recent meeting at the intersection of the philosophy of science and theoretical physics.</li>
<li>Quanta: "<a href="https://www.quantamagazine.org/20151214-graph-isomorphism-algorithm/">Landmark Algorithm</a> Breaks 30-Year Impasse."</li>
</ul>
</ul>
<ul>
<li>In audio/video media:</li>
<ul>
<li>Fermilab: "Particle Physics [<a href="https://youtu.be/SiImGVTuwGM">teenager style</a>]." [4:55]</li>
<li>SixtySymbols: "<a href="https://youtu.be/aJM5Bkdzspk">The Force</a>." [13:40]</li>
<li>In a Nutshell: "<a href="https://youtu.be/e-P5IFTqB98">Black Holes</a> Explained - From Birth to Death." [5:55]</li>
<li>MinutePhysics: "The Physics of <a href="https://youtu.be/v9ML4GA47Rg">Car Crashes</a>." [3:09]</li>
</ul>
</ul>
<div>
<b><br /></b></div>
<div>
<b>[1] </b>arXiv: "The recent observed <a href="http://arxiv.org/abs/1512.05542">diphoton resonance</a> around 750 GeV at the LHC..."</div>
<div>
<b>[2]</b> Nature News: "... the 750 GeV boson is <a href="http://www.nature.com/news/lhc-sees-hint-of-boson-heavier-than-higgs-1.19036">not one of the particles</a> that LHC physicists have been searching for..."</div>
<div>
<b>[3] </b>Tech Times: "Physicists Have <a href="http://www.techtimes.com/articles/117035/20151216/hadron-collider-finds-new-particle-gluino.htm">Discovered Evidence</a> Of A Gluino Particle, The Cousin Of The Higgs Boson."<br />
<b>[4]</b> arXiv: "It is <a href="http://arxiv.org/abs/1512.05753">already well-known</a> that a real singlet scalar ϕ with Yukawa couplings ϕXX to vector-like fermions X with mass mX>mϕ/2 can easily explain the observed signal, provided X carries both SM color and electric charge."</div>
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Bluejayhttp://www.blogger.com/profile/06935684943024856641noreply@blogger.com2tag:blogger.com,1999:blog-959149188511266512.post-25087982705614301282015-12-11T21:27:00.000+11:002015-12-11T21:31:31.419+11:00Friday wrap-up: diphoton excess?...Things feel like they're starting to wrap up for the year down here, but the holiday season might not be so laid back for us theorists...<br />
<br />
<ul>
<li>ATLAS and CMS are giving a <a href="https://indico.cern.ch/event/442432/">joint presentation</a> on 15th December: "ATLAS and CMS physics results from Run 2". The discipline is <a href="https://twitter.com/Resonaances/status/673450749041446912">abuzz</a>-<a href="https://twitter.com/freyablekman/status/673759850170597376">with</a>-<a href="https://twitter.com/anonphys/status/673915969065103360">rumours</a>-<a href="http://motls.blogspot.com.au/2015/12/atlas-cms-will-present-results-from.html">circling</a> online and in particle physics offices around the world suggesting there will be something very interesting presented indeed. The suggestion is a ~750 GeV diphoton excess at >3σ, seen by both ATLAS and CMS. If true, it seems very hard to accommodate with the absence of such a bump in Run 1, which makes it all the more interesting...<br /><div class="separator" style="clear: both; text-align: center;">
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<a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhzSmjmOSR9_dh7nOcUm34GaxH8-7TNAKx4XhoQIhchYwdwbMuIkKcPqtMVjPhs6MQUSvxvq-4CTsXgt4njpOgDCzwh2BUFRBkYlGEy_UVEq2NCruiotNv4Eu0_9q2rC7UfWBbjSUAC8_s/s1600/fig_03.png" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" height="216" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhzSmjmOSR9_dh7nOcUm34GaxH8-7TNAKx4XhoQIhchYwdwbMuIkKcPqtMVjPhs6MQUSvxvq-4CTsXgt4njpOgDCzwh2BUFRBkYlGEy_UVEq2NCruiotNv4Eu0_9q2rC7UfWBbjSUAC8_s/s320/fig_03.png" width="320" /></a></div>
<div style="text-align: center;">
<a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEiur72PkECoXBO5Oj9qzov7V7wEQxAZymiDR6rIDncF1LYEFMew29Kw9nAP1IrXQKgbaixRyb8Zahexx_kAwJPuK8obJI75kSACmeFVmIF0K8NXHkJKmUhkiJJ2gGxqSkDROnE9mDrLxa0/s1600/Screenshot+from+2015-12-11+20%253A03%253A23.png" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" height="228" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEiur72PkECoXBO5Oj9qzov7V7wEQxAZymiDR6rIDncF1LYEFMew29Kw9nAP1IrXQKgbaixRyb8Zahexx_kAwJPuK8obJI75kSACmeFVmIF0K8NXHkJKmUhkiJJ2gGxqSkDROnE9mDrLxa0/s320/Screenshot+from+2015-12-11+20%253A03%253A23.png" width="320" /></a></div>
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<div style="text-align: left;">
I was going to make some speculations here, but let us just wait until next week... I'm sure by then there'll even be a bunch of papers on the arXiv which already have the answer.<br />
<br />
We've seen anomalies come (and some go) during Run 1 (Higgs diphoton, <a href="http://syymmetries.blogspot.com.au/2015/03/friday-wrap-up-higgs-lfv-decays-higgs.html">Higgs LFV</a>, CMS kinematic edge, <a href="http://syymmetries.blogspot.com.au/2015/03/friday-wrap-up-atlas-on-z-excess-cms.html">on-Z</a>, <a href="http://syymmetries.blogspot.com.au/search/label/diboson">diboson</a>, <a href="http://syymmetries.blogspot.com.au/2015/03/friday-wrap-up-lhc-delay-b-to-k-higgs.html">B to Kμμ</a>, <a href="http://syymmetries.blogspot.com.au/2015/03/friday-wrap-up-lhc-delay-b-to-k-higgs.html">WH</a>, etc.), but the buzz around this one seems different somehow. Perhaps because it is such a clean channel, because it is hard to explain on its own, because it is in a quite unexpected place for a first signature of genuinely new physics, and because it has shown up so damn early in the new high energy data. There seems to be a strong hope that this is only part of the story, and we're excited to wake up to a reality which might be rich and complex and full of new puzzles, when, in all honesty, many were expecting a desert (I know I was). Maybe this is just the tip of the TeV-scale.<br />
<br />
Certainly the presentation is one to watch. To be continued...</div>
</li>
</ul>
<ul>
<li>First new physics searches from Run 2 have hit the arXiv: dijet searches from <a href="http://arxiv.org/abs/1512.01530">ATLAS</a> and <a href="http://arxiv.org/abs/1512.01224">CMS</a>.</li>
</ul>
<ul>
<li>There was a workshop this week called, "Why Trust a Theory? Reconsidering Scientific Methodology in Light of Modern Physics." The workshop aims to tackle questions such as: "Can a high degree of trust in an empirically unconfirmed or inconclusively confirmed theory be scientifically justified? Does the extent to which empirically unconfirmed theories are trusted today constitute a substantial change of the character of scientific reasoning? Might some important theories of contemporary fundamental physics be empirically untestable in principle?"<br /><br />Sounds very interesting, and has speakers such as Gross, Dawid, Kane, Silk, Polchinski, Dvali, et al. Some notes were also taken at <a href="https://platofootnote.wordpress.com/">this blog</a>. Unfortunately I have not had time yet to peruse the talks, but hope to get some time this week.</li>
</ul>
<ul>
<li>Some evidence <a href="http://arxiv.org/abs/1512.01239">against the</a> 3.5 keV line appeared on the arXiv.</li>
</ul>
<ul>
<li>AMVA4NewPhysics has <a href="https://amva4newphysics.wordpress.com/">a new blog</a> to follow.</li>
</ul>
<ul>
<li>Sean Carroll has finished preparation of a new book, "The Big Picture: On the Origins of Life, Meaning, and the Universe Itself." He published <a href="http://www.preposterousuniverse.com/blog/2015/12/10/the-big-picture-table-of-contents/">the Contents</a> on his blog.</li>
</ul>
<ul>
<li>Links without thinks:</li>
<ul>
<li>Quanta: "<a href="https://www.quantamagazine.org/20151208-four-mathematicians/">Math Quartet</a> Joins Forces on Unified Theory."</li>
<li>Paul Davies via Guardian: "100 years on, is this Einstein’s <a href="http://www.theguardian.com/commentisfree/2015/dec/07/einstein-universe-gravitational-waves-theory-relativity">greatest gift</a> to human understanding?"</li>
<li>Nature: "How to build <a href="http://www.nature.com/news/how-to-build-a-better-phd-1.18905">a better PhD</a>."</li>
<li>Guardian: "Chris Hadfield meets Randall Munroe: <a href="http://www.theguardian.com/lifeandstyle/2015/nov/28/conversation-chris-hadfield-randall-munroe-interview">Are we alone</a> in the universe?"</li>
<li>Quantum Frontiers: "<a href="http://quantumfrontiers.com/2015/11/28/btz-black-holes-for-blackholefriday/">BTZ</a> Black Holes."</li>
<li>Information Processing: "The <a href="http://infoproc.blogspot.com.au/2015/12/the-cult-of-genius.html">cult of genius</a>?"</li>
</ul>
</ul>
<ul>
<li>In audio/video media:</li>
<ul>
<li>Edinburgh Fringe: "The people <a href="https://youtu.be/npDmhvbiO9w">at CERN</a>" [2:59].</li>
<li>In a Nutshell: "<a href="https://youtu.be/JhHMJCUmq28">Quantum Computers</a> Explained" [7:16].</li>
<li>Numberphile: "Glitch <a href="https://youtu.be/HPfAnX5blO0">Primes and Cyclops</a> Numbers" [13:31].</li>
<li>SmarterEveryday: "<a href="https://youtu.be/Jsc-pQIMxt8">Turning Gravity</a> Into Light" [7:54].</li>
</ul>
</ul>
Bluejayhttp://www.blogger.com/profile/06935684943024856641noreply@blogger.com6tag:blogger.com,1999:blog-959149188511266512.post-33091190193833561422015-11-27T22:50:00.000+11:002016-01-09T14:23:21.782+11:00Friday wrap-up: XMASS again, Fermi...Feels like a lot of links and not much thinks this week, but we have been madly working to finish a paper before I go home for Christmas in a couple of weeks. I think we'll get there, but in the mean time...<br />
<br />
<ul>
<li>XMASS placed on the arXiv the annual modulation analysis we first saw presented at TAUP <a href="http://syymmetries.blogspot.com.au/2015/09/friday-wrap-up-xmass-multi-component.html">a couple of months back</a>, showing some preference for negative annual modulation (opposite to the DAMA/LIBRA claim). They write, "The result of a simple modulation analysis, without assuming any specific dark matter model, showed a slight negative amplitude. As the p-values are 6.1 or 17% in our two independent analyses, these results are consistent with fluctuations." However, staring at their Figure 3, I somehow just can't seem to believe it's consistent with fluctuations...<br /><br /><div class="separator" style="clear: both; text-align: center;">
<a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhJVaYmRnuxUp1hbjdx07sxJmZjD0jFQrafCTr8gt7cDz9uXRMJH25nzEe1JfUPiy80NYu5BhqxMykG-TTtnGVlfgisovjdqTt26F5dPQwsjYiB331RPXMARuUmAnE-43FDH8Q8F36-gLc/s1600/Screenshot+from+2015-11-27+22%253A26%253A59.png" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" height="348" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhJVaYmRnuxUp1hbjdx07sxJmZjD0jFQrafCTr8gt7cDz9uXRMJH25nzEe1JfUPiy80NYu5BhqxMykG-TTtnGVlfgisovjdqTt26F5dPQwsjYiB331RPXMARuUmAnE-43FDH8Q8F36-gLc/s400/Screenshot+from+2015-11-27+22%253A26%253A59.png" width="400" /></a></div>
<div class="separator" style="clear: both; text-align: center;">
<br /></div>
Sure, the fits in each bin are within 2σ of zero modulation, but there are a very large number of them below 3 keVee going the same way. If indeed the bins are largely independent (larger than resolution) and there is no correlated (annually modulating?) systematic, then at least naively I would expect that to be very improbable. So, an honest question, why is this not reflected in the p-value? An interesting sentence from the paper is, "Note that the energy bin width in Fig. 3 is one fifth of DAMA/LIBRA’s so that our limits would even get stricter with DAMA/LIBRA’s bin width." Is this suggesting that the result becomes more significant when all of those negative bins are collected into a larger bin? Comments are welcome.<br /><br />This is yet another annual modulation measurement with an intriguing result to add to the pile, and perhaps we're seeing a conservative downplaying, especially given the history of such measurements.</li>
</ul>
<ul>
<li>There's a <a href="http://www.scientificamerican.com/article/mysterious-glow-at-milky-way-s-center-could-be-dark-matter-or-hidden-pulsars/">nice article</a> at Scientific American on Fermi's <a href="http://arxiv.org/abs/1511.02938">recent contribution</a> to the galactic centre excess saga. The short story is that they confirm the excess above known backgrounds, which when fit with an diffuse NFW source is in broad agreement with previous works, as shown below (one notes the significant uncertainty in the tail as evidenced by the fits assuming different models of the background).<br /><br /><div class="separator" style="clear: both; text-align: center;">
<a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEj8fyxRhgH60m4tbhR4JtxqPp99GwfH00k_1HF6krIybGZ71xY_zrXP3FYxyHYjYZai1zRUXbXzDKu8VQLLe_tJ0iOtprYyl8WrzuacRc_1mBq7p2vJVFA3gYR1ieUZpqQJmKAL51uXC7g/s1600/Screenshot+from+2015-11-27+21%253A39%253A39.png" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" height="360" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEj8fyxRhgH60m4tbhR4JtxqPp99GwfH00k_1HF6krIybGZ71xY_zrXP3FYxyHYjYZai1zRUXbXzDKu8VQLLe_tJ0iOtprYyl8WrzuacRc_1mBq7p2vJVFA3gYR1ieUZpqQJmKAL51uXC7g/s400/Screenshot+from+2015-11-27+21%253A39%253A39.png" width="400" /></a></div>
<div style="text-align: center;">
<br /></div>
We're left now with an official analysis which confirms what we have heard for a while now: that there is definitely something unknown there. So, what is it? The leading standard astrophysical explanation is some population of unresolved point sources (such as millisecond pulsars), which <a href="http://syymmetries.blogspot.com.au/2015/07/friday-wrap-up-diboson-excess-eps-hep.html">Slatyer now claims</a> are favoured by the data. Still, the dark matter hypothesis is alive, albeit grappling with <a href="http://syymmetries.blogspot.com.au/2015/03/friday-wrap-up-atlas-on-z-excess-cms.html">limits from</a> dwarf spheroidals. And perhaps it can be settled soon; one thing I learned from the SA article is that the pulsar hypothesis might be probed in the near future:<br /><br /><i>The good news is that if pulsars are behind the excess, more powerful, telescopes in the future should be able to spot the too-faint spinning stars directly. Pulsars would be prime targets for next-generation radio telescopes... “Should we fail to find them in the next five or ten years, a dark matter explanation becomes more likely again,” Weniger says. “This is pretty much a win–win situation. But we have to be patient.”</i></li>
</ul>
<ul>
<li>Tommaso Dorigo has found a publisher for <a href="http://www.science20.com/a_quantum_diaries_survivor/anomaly_a_different_particle_physics_book-160305">his book</a> on the Tevatron (and in particular CDF), "Anomaly! - Scientific Discoveries and the Quest for the Unknown." Should be out end of 2016; very much looking forward to it.</li>
</ul>
<ul>
<li>Links without thinks...</li>
<ul>
<li>Starts With a Bang: "Strange But True: Dark Matter <a href="http://www.forbes.com/sites/startswithabang/2015/11/24/strange-but-true-dark-matter-grows-hair-around-stars-and-planets/">Grows 'Hair'</a> Around Stars And Planets."</li>
<li>SLAC: "Q&A: SLAC Theorist Lance Dixon Explains <a href="https://www6.slac.stanford.edu/news/2015-11-18-qa-slac-theorist-lance-dixon-explains-quantum-gravity.aspx">Quantum Gravity</a>."</li>
<li>New Yorker: "The Space Doctor's <a href="http://www.newyorker.com/tech/elements/the-space-doctors-big-idea-einstein-general-relativity">Big Idea</a>," the Special Theory of Relativity explained in the 1000 most used words in the English language, by xkcd artist Randall Munroe, who also has a <a href="http://xkcd.com/thing-explainer/">related book</a> out. </li>
<li>New Yorker: "The <a href="http://www.newyorker.com/magazine/2015/11/23/doomsday-invention-artificial-intelligence-nick-bostrom">Doomsday Invention</a>," a long read on artificial intelligence; do yourself a favour and get your hands on Nick Bostrom's very interesting book!</li>
<li>Nature: "Einstein was <a href="http://www.nature.com/news/history-einstein-was-no-lone-genius-1.18793">no lone genius</a>."</li>
<li>Nature: "The <a href="http://www.nature.com/news/the-quantum-source-of-space-time-1.18797">quantum source</a> of space-time."</li>
<li>Preposterous Universe: "<a href="http://www.preposterousuniverse.com/blog/2015/11/26/thanksgiving-10/">Thanksgiving</a> [for Riemannian Geometry]"</li>
<li>Wired: "Physicists Are Desperate to Be <a href="http://www.wired.com/2015/11/physicists-are-desperate-to-be-wrong-about-the-higgs-boson/">Wrong About</a> the Higgs Boson."</li>
</ul>
</ul>
<ul>
<li>In audio/video media...</li>
<ul>
<li>Claire Lee via TEDx: Our universe <a href="https://youtu.be/LgNiVK0EkCg">in a box</a>, particle physics with Lego. [15:46]</li>
<li>Fermilab: What good is <a href="https://youtu.be/sTt27A8W4eY">particle physics</a>? [6:48]</li>
<li>Fermilab: <a href="https://youtu.be/LEhw01FsFc4">Physics Slam</a> 2015. [1:29:47]</li>
<li>WaitWait: <a href="https://soundcloud.com/waitwait/lisa-randall-extended-interview">Lisa Randall</a> Interview. [22:36]</li>
<li>Einstein 100: Theory of <a href="https://youtu.be/6XSAVqm0XBI">General Relativity</a>, a short narrated by David Tennant. [3:04]</li>
<li>SixtySymbols: Einstein's <a href="https://youtu.be/nJsFsjSWYx0">Famous Blunder</a>. [18:47]</li>
<li>SmarterEveryday: Hovering <a href="https://youtu.be/eXR1olg_I0w">a Helicopter</a> is Hilariously Hard. [9:44]</li>
<li>Veritasium: How Long Will <a href="https://youtu.be/_dDqFB-PjWg">You Live</a>? [6:25]</li>
<li>Numberphile: <a href="https://youtu.be/ktPvjr1tiKk">Tic-Tac-Toe</a> (with Xs only). [7:19]</li>
</ul>
</ul>
Bluejayhttp://www.blogger.com/profile/06935684943024856641noreply@blogger.com1tag:blogger.com,1999:blog-959149188511266512.post-12715135685288571542015-11-14T09:24:00.000+11:002015-11-14T09:30:01.923+11:00Friday wrap-up: 4/fb, Fermi...Another two week break, but plenty happened this week!<br />
<br />
<ul>
<li>The LHC has finished collecting proton-proton collision data for the year. ATLAS ended up <a href="https://atlas.web.cern.ch/Atlas/GROUPS/DATAPREPARATION/PublicPlots/2015/DataSummary/figs/sumLumiByDay.png">with ~4.0/fb</a>, and CMS <a href="http://cms-service-lumi.web.cern.ch/cms-service-lumi/publicplots/int_lumi_per_day_cumulative_pp_2015.png">with ~3.6/fb</a>.</li>
</ul>
<ul>
<li>Fermi Collaboration have released <a href="http://arxiv.org/abs/1511.02938">their own analysis</a> of the galactic centre excess. I have not had time to read the paper in detail (not that I could comment with much authority even if I had), but it is interesting that they seem to see a residual excess after subtracting known sources, which can be somewhat accounted for by a peaking template (dark matter?). Perhaps we will know more by next week...<br /><br /><div class="separator" style="clear: both; text-align: center;">
<a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhJN4kaKOcv-alh_Yjkz0em4JvC0JKxeqvYygq1B-35Ymr8oO5k-N-cWVn16SJMk5tDb-wmRXzlHfoTMzoGIMWcL5GFGUuUB4006j_8BCEFqk2X_yuECsblUqYH2lh0aQvvlvfQO2WHyKU/s1600/Screenshot+from+2015-11-14+09%253A27%253A08.png" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" height="348" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhJN4kaKOcv-alh_Yjkz0em4JvC0JKxeqvYygq1B-35Ymr8oO5k-N-cWVn16SJMk5tDb-wmRXzlHfoTMzoGIMWcL5GFGUuUB4006j_8BCEFqk2X_yuECsblUqYH2lh0aQvvlvfQO2WHyKU/s400/Screenshot+from+2015-11-14+09%253A27%253A08.png" width="400" /></a></div>
<br />There's a layperson article from <a href="http://www.economist.com/news/science-and-technology/21678126-powerful-gamma-rays-centre-milky-way-look-ever-more-signs">The Economist</a> about it which says, "There are still a few die-hards who do not believe in hooperons"! Well, call me a die-hard.</li>
</ul>
<ul>
<li>The XENON1T direct detection experiment at Gran Sasso was inaugurated on Wednesday. Read the <a href="https://www.lngs.infn.it/en/news/xenon-inauguration">press release here</a>; they write, "Once fully operational, XENON1T will be the most sensitive dark matter experiment in the world. The detector installation has been completed just a few days ago and the first tests of its performance have already been started. The first science results are expected early 2016, as only one week of good data is sufficient to yet again take the lead in the field." And some cool pictures:<br /><br /><div class="separator" style="clear: both; text-align: center;">
<a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhyamIAgMBQUfNhUoIvrTN9suFaEy2PWvOke7CF58oLgrJ_JduA54Y4NPqg015Fod3QHVvpdZSf9WQIARlwOHSf_i8Zh6JYtW5OuU33EwjqNZ7vczo6awltzfXc8_m_pOrKD51LlcWwr5I/s1600/xenon_press_release2.jpg.jpg" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" height="300" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhyamIAgMBQUfNhUoIvrTN9suFaEy2PWvOke7CF58oLgrJ_JduA54Y4NPqg015Fod3QHVvpdZSf9WQIARlwOHSf_i8Zh6JYtW5OuU33EwjqNZ7vczo6awltzfXc8_m_pOrKD51LlcWwr5I/s400/xenon_press_release2.jpg.jpg" width="400" /></a></div>
<div style="text-align: center;">
<a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhbGJw37kwVM_4zwCdwNPEP3fICizIwGN8nNOxpT4uMlfRWf-dLxRMfEPoJS79HK560Uz2f7nrNruxlnEVrJLAi9TXfCSWrhtP3s0NYvz9qi2dUK2agiQXS_96bhOwRl7oAVd2GhSxJOhc/s1600/xenon_press_release3.jpg.jpg" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" height="298" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhbGJw37kwVM_4zwCdwNPEP3fICizIwGN8nNOxpT4uMlfRWf-dLxRMfEPoJS79HK560Uz2f7nrNruxlnEVrJLAi9TXfCSWrhtP3s0NYvz9qi2dUK2agiQXS_96bhOwRl7oAVd2GhSxJOhc/s400/xenon_press_release3.jpg.jpg" width="400" /></a></div>
<div class="separator" style="clear: both; text-align: center;">
<br /></div>
</li>
</ul>
<ul>
<li>The $3mil Breakthrough Prize in Fundamental Physics was awarded for the experiments which established neutrino oscillations (the decision was made before the Nobel Prizes were known). The prize was shared equally among the Daya Bay, K2K/T2K, KamLAND, SNO, and Super K collaborations, with two-thirds of each share to <a href="https://breakthroughprize.org/Laureates/1/P1">the leaders</a> and one-third to the remaining collaboration members: 1370 physicists in all! It is nice to see all of these scientists recognised. <br /><br />The Symposium and Panel Discussion are <a href="https://www.youtube.com/playlist?list=PLOyuQaVrp4qph9yQJPMeLst62iZ5M2Yrk">on YouTube</a>. The Fundamental Physics talks are on the future of particle physics and feature Nima Arkani-Hamed, Lawrence Hall, Beate Heinemann, Gabriel Orebi Gann, and Tom Shutt.</li>
</ul>
<ul>
<li>Worth reading are two articles, one a piece by Ed Witten, "What <a href="http://scitation.aip.org/content/aip/magazine/physicstoday/article/68/11/10.1063/PT.3.2980">every physicist</a> should know about string theory," and another <a href="http://thewire.in/2015/10/29/good-scientists-solve-problems-but-great-scientists-know-whats-worth-solving-14279/">an interview with</a> Abhay Ashtekar broken into four parts: 1. Getting started on gravity and cosmology; 2. Learning from Chandra; 3. Challenges in loop quantum gravity; 4. Arrogance in string theory.<br /><br />Of course these are bat-signals for <a href="http://www.math.columbia.edu/~woit/wordpress/?p=8068">Woit</a> and/or <a href="http://motls.blogspot.com.au/2015/11/abhay-ashtekar-and-uniqueness-of-string.html">Motl</a>, so click their names to read their reactions/reflections too.</li>
</ul>
<ul>
<li>The <a href="http://www.interactions.org/cms/?pid=6001">people's choice voting</a> is open for photographs from the InterActions Physics Photowalk, featuring shots of CERN, DESY, FermiLab, INFN, KEK, SLAC, SUPL, and TRIUMF.</li>
</ul>
<ul>
<li>Conferences/workshops:</li>
<ul>
<li>Data Science @ LHC 2015 Workshop: <a href="http://indico.cern.ch/event/395374/other-view?view=standard#20151109.detailed">indico</a>, <a href="https://twitter.com/hashtag/DSLHC15">hashtag</a>.</li>
<li>KIAS-CFHEP Workshop and 5th KIAS Workshop on Particle Physics and Cosmology: <a href="https://indico.kias.re.kr/indico/event/3/timetable/#20151113.detailed">indico</a>, and live blog from <a href="http://perfectpuddle.blogspot.com.au/2015_11_01_archive.html">A Perfectly Formed Puddle</a>.</li>
<li>UK HEP Forum: Anomalies and Deviations: <a href="https://conference.ippp.dur.ac.uk/event/472/timetable/#20151105.detailed">indico</a>.</li>
<li>LHC Heavy Flavour WG public meeting: <a href="http://indico.cern.ch/event/455246/other-view?view=standard">indico</a>.</li>
<li>dotAstronomy 7: <a href="http://dotastronomy.com/events/seven/">website</a>, <a href="https://twitter.com/dotastronomy">twitter</a>, <a href="https://twitter.com/hashtag/dotastro?src=hash">hashtag</a>.</li>
</ul>
</ul>
<ul>
<li>Links without thinks:</li>
<ul>
<li>There's some buzz about a quasipolynomial time algorithm for the graph isomorphism problem. See <a href="http://jeremykun.com/2015/11/12/a-quasipolynomial-time-algorithm-for-graph-isomorphism-the-details/">this blog</a> for a (research-level) detailed description. Else for the layperson see <a href="http://news.sciencemag.org/math/2015/11/mathematician-claims-breakthrough-complexity-theory">Science</a>, <a href="https://www.newscientist.com/article/dn28478-complex-problem-made-simple-sends-computer-scientists-wild/">New Scientist</a>, or <a href="http://motherboard.vice.com/en_uk/read/graph-isomorphism-youve-been-served">Motherboard</a>.</li>
<li>Nautilus: "Will Quantum Mechanics <a href="http://nautil.us/issue/29/scaling/will-quantum-mechanics-swallow-relativity">Swallow Relativity</a>? The contest between gravity and quantum physics takes a new turn."</li>
<li>Dan Waddell via Medium: "Saving <a href="https://medium.com/@danwaddell/saving-tim-hunt-97db23c6ee93">Tim Hunt</a>," a long read on the Tim Hunt story.</li>
<li>Thesis Whisperer: "<a href="http://thesiswhisperer.com/2013/02/13/academic-assholes/">Academic assholes</a> and the circle of niceness."</li>
<li>Nature: "Networking: <a href="http://www.nature.com/naturejobs/science/articles/10.1038/nj7575-729a">Hello, stranger</a>," on conference etiquette and career development.</li>
<li>Existential Comics: "<a href="http://existentialcomics.com/comic/106">Trolley Madness</a>."</li>
</ul>
</ul>
<ul>
<li>In audio/video media:</li>
<ul>
<li>2016 Breakthrough Prize Symposium in Fundamental Physics, with: 1. Nima Arkani-Hamed - Motivations for 100km Circular Colliders; 2. Lawrence Hall - New Searches for Dark Matter in Particle Collisions; 3. Beate Heinemann - The LHC and beyond: what can colliders teach us?; 4. Gabriel Orebi Gann - Unravelling the Secrets of the Universe with Neutrinos; 5. Tom Shutt - The Hunt for Dark Matter. [1:36:49]</li>
<li>CBS 60 Minutes: "<a href="http://www.cbsnews.com/news/extra-dimensions-dark-matter-a-more-powerful-collider-hunts-for-clues/">The Collider</a>," on the LHC. [11:54]</li>
<li>Catalyst: "Einstein's <a href="http://www.abc.net.au/catalyst/stories/4348650.htm">Extraordinary Universe</a>", featuring visits to LHC, Gran Sasso, and LIGO. [28:17]</li>
<li>WHYY RadioTimes: with Lisa Randall on dark matter and <a href="http://whyy.org/cms/radiotimes/2015/11/09/physicist-lisa-randall-on-everything-we-need-to-know-about-dark-matter/">the dinosaurs</a>. [48:57]</li>
<li>MinutePhysics: "How to go <a href="https://youtu.be/2p_8gx-XHJo">to space</a>," Thing Explainer edition. [2:57]</li>
<li>Numberphile: "The <a href="https://youtu.be/wymmCdLdPvM">Uncracked Problem</a> with 33". [8:28]</li>
</ul>
</ul>
Bluejayhttp://www.blogger.com/profile/06935684943024856641noreply@blogger.com0tag:blogger.com,1999:blog-959149188511266512.post-36159577086756469192015-10-31T15:16:00.002+11:002015-10-31T15:16:44.129+11:00Friday wrap-up: Chinese collider...Not too much happening lately, or perhaps I have been keeping too busy with other things? Either way, we had a week away; so here's some news from the last two weeks.<br />
<br />
<ul>
<li>A number of articles <a href="http://www.theguardian.com/science/2015/oct/29/china-supercollider-higgs-boson-science-leader">appeared yesterday</a> saying that state-run Chinese media is reporting (as has been brewing for a while now) China will begin building the next supercollider in 2020. Here's hoping they carry through with it! As well this week, Phase II (<a href="http://press.web.cern.ch/press-releases/2015/10/lhc-luminosity-upgrade-project-moving-next-phase">prototyping</a>) of the HL-LHC project has begun.</li>
</ul>
<ul>
<li>Lisa Randall's book "<a href="http://www.amazon.com/Dark-Matter-Dinosaurs-Astounding-Interconnectedness/dp/0062328476">Dark Matter and the Dinosaurs</a>" is now available; read an <a href="http://www.sciencefriday.com/articles/cosmic-connections-dark-matter-and-the-dinosaurs/">excerpt here</a>.</li>
</ul>
<ul>
<li>Links without thinks:</li>
<ul>
<li>Tommaso Dorigo's story of first <a href="http://www.science20.com/a_quantum_diaries_survivor/shopping_around_for_a_postdoc-158503">post-doctoral position</a> interviews.</li>
<li>Quanta: Q&A with Gabriela González of <a href="https://www.quantamagazine.org/20151022-ligo-gravitational-waves-gabriela-gonzalez/">Advanced LIGO</a>, and "The Physical Origin of <a href="https://www.quantamagazine.org/20151027-the-physical-origin-of-universal-computing/">Universal Computing</a>."</li>
<li>BackReaction: "What is <a href="http://backreaction.blogspot.com.au/2015/10/what-is-basic-science-and-what-is-it.html">basic science</a> and what is it good for?"</li>
</ul>
</ul>
<ul>
<li>In video/audio media:</li>
<ul>
<li>Hitoshi Murayama: When a Symmetry Breaks, <a href="http://www.cornell.edu/video/hitoshi-murayama-when-symmetry-breaks">physics colloquium</a> at Cornell [1:02:45].</li>
<li>US LHC: Back to <a href="https://youtu.be/VgZ2EFYRQ-k">the Future</a> and CERN [2:45].</li>
<li>Sixty Symbols: The Science <a href="https://youtu.be/GyLeBMdI_HU">of Drumming</a> [9:03].</li>
<li>Numberphile: <a href="https://youtu.be/Lihh_lMmcDw">Skewes' Number</a> [10:25], and the <a href="https://youtu.be/AxxnziuL408">Shape of DNA</a> [9:10].</li>
</ul>
</ul>
<ul>
<li><div style="text-align: left;">
Ending with some visual delights, here is François Moncarey’s projection mapping work which opened TEDxCERN:</div>
<div style="text-align: center;">
<br /></div>
<div style="text-align: center;">
<iframe allowfullscreen="" frameborder="0" height="500" mozallowfullscreen="" src="https://player.vimeo.com/video/142364749" webkitallowfullscreen="" width="500"></iframe></div>
</li>
<li>A few days ago the Cassini spacecraft performed its <a href="http://www.nasa.gov/feature/jpl/saturns-geyser-moon-shines-in-close-flyby-views">deepest ever dive</a> through the southern plumes of Saturn's moon Enceladus (and returned some incredible images).<br /><br /><div style="text-align: center;">
<a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhw2a2gi78AADRPZzVVI9Vbyl2Ikh507GqcAlvJ8WiVtI4LPEHz9Oe5Fh_OOvo7CnRUTO8P4JljuVwXwMk0GPwMyo0FyDUz5OvrKyrgHtQPdLoNPJRnlejZ21GxwHME48-2V30ZTtKklBc/s1600/pia17203.jpg" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" height="400" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhw2a2gi78AADRPZzVVI9Vbyl2Ikh507GqcAlvJ8WiVtI4LPEHz9Oe5Fh_OOvo7CnRUTO8P4JljuVwXwMk0GPwMyo0FyDUz5OvrKyrgHtQPdLoNPJRnlejZ21GxwHME48-2V30ZTtKklBc/s400/pia17203.jpg" width="400" /></a></div>
</li>
</ul>
Bluejayhttp://www.blogger.com/profile/06935684943024856641noreply@blogger.com0tag:blogger.com,1999:blog-959149188511266512.post-84708004181389101622015-10-16T15:24:00.002+11:002015-10-16T15:24:44.595+11:00Friday wrap-up: Marcy...Wherein I list some (mostly) recent happenings, ramble a bit, and provide links, in an order roughly determined by importance and relevance to particle physics. Views are my own. Content very definitely skewed by my own leanings and by papers getting coverage, and it may not even be correct. It is a blog after all...<br />
<div>
<br /></div>
<div>
<ul>
<li>Geoff Marcy resigned from the Berkeley astronomy department after it was found he sexually harassed students (and after the majority of the department signed <a href="http://www.nytimes.com/interactive/2015/10/14/science/updated-berkeley-astronomy-statement.html">this letter</a>); see the NY Times article <a href="http://www.nytimes.com/2015/10/15/science/geoffrey-marcy-to-resign-from-berkeley-astronomy-department.html">here</a> (who themselves <a href="http://www.astronomy.ohio-state.edu/~lopez.513/Letter/Letter_to_NY_Times.html">were accused</a> in an open letter of taking an empathetic stance in an <a href="http://www.nytimes.com/2015/10/11/science/astronomer-apologizes-for-behavior.html">earlier article</a>). See also <a href="https://medium.com/starts-with-a-bang/how-did-geoff-marcy-happen-103a37a7ce01">Ethan Siegel</a> and links therein.</li>
</ul>
<ul>
<li>CosPA 2015 (<a href="https://indico.ibs.re.kr/event/21/other-view?view=standard">indico</a>) was on this week.</li>
</ul>
<ul>
<li>APS gave out some prizes: a new award, the <a href="http://www.aps.org/programs/honors/prizes/apsmedal.cfm">APS Medal</a> for Exceptional Achievement in Research went to Ed Witten, and the J.J. Sakurai Prize for <a href="http://www.aps.org/programs/honors/prizes/prizerecipient.cfm?last_nm=Lepage&first_nm=G&year=2016">Theoretical Particle Physics</a> went to Peter Lepage.</li>
</ul>
<ul>
<li>Links without thinks...</li>
<ul>
<li>Symmetry: Xenon, <a href="http://www.symmetrymagazine.org/article/october-2015/xenon-xenon-everywhere">xenon everywhere</a>.</li>
<li>The Atlantic: The Most <a href="http://www.theatlantic.com/science/archive/2015/10/the-most-interesting-star-in-our-galaxy/410023/">Mysterious Star</a> in Our Galaxy.</li>
</ul>
</ul>
<ul>
<li>In audio/video media:</li>
<ul>
<li>Talk Python to Me Podcast: Python <a href="http://talkpython.fm/episodes/show/29/python-at-the-large-hadron-collider-and-cern">at the LHC</a> and CERN. [52:09]</li>
<li>Neutrino Rap: Neutrinos (<a href="https://youtu.be/EI5EZlVyduI">Tiny Ghosts</a>). [4:09]</li>
<li>Webinar from Diego Aristizábal: <a href="https://youtu.be/qbc210MgC24">Leptogenesis beyond</a> Type-I seesaw. [1:19:40] </li>
<li>Radio Sweden: How to Win <a href="http://sverigesradio.se/sida/avsnitt/629054?programid=2054">a Nobel Prize</a>. [~30:00]</li>
</ul>
</ul>
<ul>
<li><div style="text-align: left;">
NASA released high resolution Apollo 11 photographs <a href="https://www.flickr.com/photos/projectapolloarchive/albums">on flickr</a> not too long ago. Planetary Society made a great video out of them:</div>
<div style="text-align: center;">
<br /></div>
<div style="text-align: center;">
<iframe allowfullscreen="" frameborder="0" height="315" src="https://www.youtube.com/embed/Kl7ZJZn36qg" width="420"></iframe></div>
</li>
</ul>
</div>
Bluejayhttp://www.blogger.com/profile/06935684943024856641noreply@blogger.com1tag:blogger.com,1999:blog-959149188511266512.post-31879010732672684162015-10-10T10:04:00.003+11:002015-10-10T10:04:34.749+11:00Friday wrap-up: neutrino Nobel Prize...Wherein I list some (mostly) recent happenings, ramble a bit, and provide links, in an order roughly determined by importance and relevance to particle physics. Views are my own. Content very definitely skewed by my own leanings and by papers getting coverage, and it may not even be correct. It is a blog after all...<br />
<div>
<br /></div>
<br />
<ul>
<li>The Nobel Prize in Physics 2015 was awarded jointly to Takaaki Kajita and Arthur B. McDonald "for the discovery of neutrino oscillations, which shows that neutrinos have mass." See the plethora of articles already online: <a href="http://www.nobelprize.org/nobel_prizes/physics/laureates/2015/">Nobel Prize site</a>, <a href="http://www.aps.org/publications/apsnews/updates/nobel15.cfm">APS</a>, <a href="http://home.web.cern.ch/about/updates/2015/10/neutrinos-after-nobel-prize-hunt-continues">CERN</a>, <a href="http://www.symmetrymagazine.org/article/october-2015/nobel-prize-awarded-for-discovery-of-neutrino-oscillations">symmetry</a>, <a href="https://theconversation.com/how-neutrinos-which-barely-exist-just-ran-off-with-another-nobel-prize-48726">Conversation</a>, <a href="http://www.newyorker.com/news/daily-comment/what-neutrinos-reveal?intcid=mod-latest">New Yorker</a>, <a href="http://www.forbes.com/sites/matthewfrancis/2015/10/06/2015-nobel-prize-in-physics-the-discovery-of-neutrino-oscillations/">Forbes</a>...<br /><br /><div class="separator" style="clear: both; text-align: center;">
<a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhM55s01RAX8xXgsUjEfbg0p6kQrgiaxTSE1KJYKJlbg3wkKhVcj2ewt232j0_6S4S9DfhlCIaldsE10teqwDU8DiPaCI5oTmMhGqZ-Nc56mQr5I5sgK10dAhQVS6uUKKoTSjASwku7BdQ/s1600/CQoAgspU8AAUNl8.jpg" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" height="400" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhM55s01RAX8xXgsUjEfbg0p6kQrgiaxTSE1KJYKJlbg3wkKhVcj2ewt232j0_6S4S9DfhlCIaldsE10teqwDU8DiPaCI5oTmMhGqZ-Nc56mQr5I5sgK10dAhQVS6uUKKoTSjASwku7BdQ/s400/CQoAgspU8AAUNl8.jpg" width="400" /></a></div>
<div style="text-align: center;">
<br /></div>
</li>
<li>TEDxCERN (rulebreakers and visionaries) was on Friday; find the <a href="http://tedxcern.web.cern.ch/video">videos here</a>.</li>
</ul>
<ul>
<li>An <a href="http://www.nature.com/news/the-biggest-mystery-in-mathematics-shinichi-mochizuki-and-the-impenetrable-proof-1.18509">interesting article</a> on Mochizuki and his proposed proof of the <i>abc</i> conjecture.</li>
</ul>
<ul>
<li>In video/audio media:</li>
<ul>
<li>Sixty Symbols: <a href="https://youtu.be/XQHw7qQrpf0">Neutrino Nobel Prize</a>. [8:01]</li>
<li>Big Think: <a href="https://youtu.be/rheKIzEAmv0">Wilczek reflects</a> on his Nobel. [6:57]</li>
<li>Numberphile: <a href="https://youtu.be/pKwsPBeSiOc">Powers of 2</a>. [6:10]</li>
</ul>
</ul>
Bluejayhttp://www.blogger.com/profile/06935684943024856641noreply@blogger.com0tag:blogger.com,1999:blog-959149188511266512.post-85068183091547179642015-10-03T15:08:00.001+10:002015-10-03T15:08:12.999+10:00Friday wrap-up: 1/fb, various links...Wherein I list some (mostly) recent happenings, ramble a bit, and provide links, in an order roughly determined by importance and relevance to particle physics. Views are my own. Content very definitely skewed by my own leanings and by papers getting coverage, and it may not even be correct. It is a blog after all...<br />
<br />
<ul>
<li>A huge amount of data was accumulated this week. ATLAS <a href="https://twiki.cern.ch/twiki/bin/view/AtlasPublic/LuminosityPublicResultsRun2">surpassed 1/fb</a> of integrated luminosity, and at the time of this writing is sitting at >1.4/fb!<br /><br /><div class="separator" style="clear: both; text-align: center;">
<a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhmWiM843VCirfRmEn2ooe-ePNOVoQTapQeD3z3OgJ4mtCNPPQ9KM5_4Too_Fm40zknq_qPw-B6eRFB7a7nduD_jTx64l83cHK15L2i2G54glTnHPyEWjmKiubMBw3zqt3cmZSTStl-R-4/s1600/sumLumiByDay.png" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" height="229" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhmWiM843VCirfRmEn2ooe-ePNOVoQTapQeD3z3OgJ4mtCNPPQ9KM5_4Too_Fm40zknq_qPw-B6eRFB7a7nduD_jTx64l83cHK15L2i2G54glTnHPyEWjmKiubMBw3zqt3cmZSTStl-R-4/s320/sumLumiByDay.png" width="320" /></a><br /></div>
</li>
</ul>
<ul>
<li>A rumour emerged last weekend of gravitational wave discovery at LIGO; there's a <a href="http://www.nature.com/news/has-giant-ligo-experiment-seen-gravitational-waves-1.18449">nature column</a> claiming it is unlikely and/or just a drill.<br /><blockquote class="twitter-tweet" lang="en">
<div dir="ltr" lang="en">
Rumor of a gravitational wave detection at LIGO detector. Amazing if true. Will post details if it survives.</div>
— Lawrence M. Krauss (@LKrauss1) <a href="https://twitter.com/LKrauss1/status/647510799678750720">September 25, 2015</a></blockquote>
<script async="" charset="utf-8" src="//platform.twitter.com/widgets.js"></script></li>
<li>The Quark Matter 2015 conference (<a href="https://indico.cern.ch/event/355454/">indico</a>; <a href="https://twitter.com/hashtag/qm2015?f=tweets&vertical=default&src=hash">hashtag</a>) was on this week.</li>
</ul>
<ul>
<li>The CMS Experiment has a new outreach initiative: <a href="https://twitter.com/CMSvoices">CMS Voices</a> on twitter, with a new CMS physicist every month.</li>
</ul>
<ul>
<li>Links without thinks:</li>
<ul>
<li>Wall Street Journal: "China's Great <a href="https://www.google.com.au/webhp?sourceid=chrome-instant&ion=1&espv=2&ie=UTF-8#q=China%E2%80%99s+Great+Scientific+Leap+Forward+-+WSJ">Scientific Leap</a> Forward," an opinion piece from Gross and Witten [behind a paywall but for me is accessible via a Google search].</li>
<li>Life and Physics by Jon Butterworth: "Fermilab's <a href="http://www.theguardian.com/science/life-and-physics/2015/sep/27/fermilabs-giant-magnet-begins-its-journey-into-the-quantum-badlands">giant magnet</a> begins its journey into the quantum badlands," on the muon $g-2$ experiment which began this week at Fermilab.</li>
<li>Nautilus: "The Trouble with <a href="http://nautil.us/issue/29/scaling/the-trouble-with-theories-of-everything">Theories of Everything</a>," from Lawrence Krauss.</li>
<li>Backreaction has been busy: "No, Loop Quantum Gravity <a href="http://backreaction.blogspot.com.au/2015/09/no-loop-quantum-gravity-has-not-been.html">has not been</a> shown to violate the Holographic Principle," and "When string theorists are out of luck, <a href="http://backreaction.blogspot.com.au/2015/10/when-string-theorists-are-out-of-luck.html">will Loop Quantum Gravity</a> come to rescue?"</li>
<li>Terence Tao has submitted a solution to the Erdős discrepancy problem, motivated by a suggestive comment on his blog; see articles at <a href="http://www.nature.com/news/maths-whizz-solves-a-master-s-riddle-1.18441">nature news</a>, and <a href="https://www.quantamagazine.org/20151001-tao-erdos-discrepancy-problem/">Quanta</a>.</li>
</ul>
</ul>
<ul>
<li>In audio/video media:</li>
<ul>
<li>A <a href="https://www.quantamagazine.org/?powerpress_pinw=18636-podcast">podcast</a> of Quanta's Nima article from last week. [33:17]</li>
<li>Bed & Roses TV: <a href="https://youtu.be/1Dxp6dvZnFk">Krauss</a> on the nature of the Universe. [21:45]</li>
<li>Numberphile: <a href="https://youtu.be/ZREp1mAPKTM">Fold and Cut</a> Theorem; Pi and the <a href="https://youtu.be/d0vY0CKYhPY">Mandelbrot Set</a>. [9:30]</li>
</ul>
</ul>
<ul>
<li>Myriad awesome images emerged from NASA this week of "recurring slope lineae" on Mars, <a href="http://www.nasa.gov/press-release/nasa-confirms-evidence-that-liquid-water-flows-on-today-s-mars">hypothesised</a> to be formed by the flow of briny liquid water. See <a href="http://www.planetary.org/blogs/emily-lakdawalla/2015/09281219-nasas-mars-announcement.html">Emily Lakdawalla's blog</a> for a scientist's take.<br /><br /><div class="separator" style="clear: both; text-align: center;">
<a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgufCV9qsErQ9aMc3lQP1JZkseMi63AUUM3GkIOd-2fEhuifHpj3-hCZJ3PfmXoACHRzsEgjum5vtGQ19jW1sFjmHt4va5cFINRsgtr6oqOybQPKpoTj_w-rx3y8ddw5ykZtgagscN5Q68/s1600/pia19917_perspective_6.jpg" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" height="207" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgufCV9qsErQ9aMc3lQP1JZkseMi63AUUM3GkIOd-2fEhuifHpj3-hCZJ3PfmXoACHRzsEgjum5vtGQ19jW1sFjmHt4va5cFINRsgtr6oqOybQPKpoTj_w-rx3y8ddw5ykZtgagscN5Q68/s400/pia19917_perspective_6.jpg" width="400" /></a></div>
<div style="text-align: center;">
<br /></div>
</li>
</ul>
Bluejayhttp://www.blogger.com/profile/06935684943024856641noreply@blogger.com0tag:blogger.com,1999:blog-959149188511266512.post-31980038450314166132015-09-25T16:42:00.001+10:002015-09-25T16:42:30.131+10:00Friday wrap-up: Nima, weakly coupled high-scale physics...Wherein I list some (mostly) recent happenings, ramble a bit, and provide links, in an order roughly determined by importance and relevance to particle physics. Views are my own. Content very definitely skewed by my own leanings and by papers getting coverage, and it may not even be correct. It is a blog after all...<br />
<br />
<ul>
<li>There is an article at Quanta Magazine constructed around a <a href="https://www.quantamagazine.org/20150922-nima-arkani-hamed-collider-physics/">profile of Nima Arkani-Hamed</a> that is well worth a read. It includes his (and others') visions of and predictions for the future of high-energy physics, and the important role the Chinese might play in constructing a 100 TeV collider.</li>
</ul>
<ul>
<li>A few things wrapped up for me this week... <br /><br />(1) Uploaded to the arXiv v2 of a paper on <a href="http://arxiv.org/abs/1505.00063">displaced Higgs decays</a> (see blog from <a href="http://syymmetries.blogspot.com.au/2015/05/friday-wrap-up-collisions-displaced.html">back in June</a>). In particular, the new version has the plots updated and include some <a href="http://syymmetries.blogspot.com.au/2015/08/friday-wrap-up-3fb-atlas-on-higgs-lfv.html">recent results</a>. Besides the scientific content, at the very least they are pleasing to the eye (well at least to mine)! I find this kind of phenomenology very interesting, and there is certainly more to be said in conversation between phenomenologists and experimentalists on where to search and how to present results for displaced physics.<br /><br /><div class="separator" style="clear: both; text-align: center;">
<a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjuUhvG2lgdLsnbLCTzipH7IUm7DtaDCcCG6HtSbnnfAjhLIeIBsCCl_NESi0a2_iia1HuauYxhdYkr-ZxSIt98m4rbsBvTig5y1fTGM1Ej68l5_UdqwDURS1wFQOyKRXWPHWJxIYvGdj0/s1600/Screenshot+from+2015-09-24+10%253A35%253A47.png" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" height="266" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjuUhvG2lgdLsnbLCTzipH7IUm7DtaDCcCG6HtSbnnfAjhLIeIBsCCl_NESi0a2_iia1HuauYxhdYkr-ZxSIt98m4rbsBvTig5y1fTGM1Ej68l5_UdqwDURS1wFQOyKRXWPHWJxIYvGdj0/s400/Screenshot+from+2015-09-24+10%253A35%253A47.png" width="400" /></a></div>
<div style="text-align: center;">
<br />
<div style="text-align: left;">
(2) Uploaded to the arXiv <a href="http://arxiv.org/abs/1509.07242">a conference proceedings</a> (PLANCK) summarising two recent papers: "<b>How to avoid unnatural hierarchical thermal leptogenesis</b>." If you'd like to know why explaining baryogenesis and neutrino masses with the minimal three-flavour Type I seesaw and hierarchical leptogenesis is necessarily unnatural, and the various ways around it, this document should serve as a good summary. Or see the <a href="http://syymmetries.blogspot.com.au/2015/05/friday-wrap-up-13-tev-natural.html">blog post</a> from May for an even shorter summary. The second part of the proceedings describes a two-Higgs-doublet model with right-handed neutrinos (ν2HDM) which can achieve hierarchical leptogenesis and realise the neutrino masses without introducing a naturalness problem. This model serves as the basis for the following...<br />
<br />
(3) Uploaded an <a href="http://arxiv.org/abs/1509.07243">arXiv preprint</a> titled: "<b>νDFSZ: a technically natural non-supersymmetric model of neutrino masses, baryogenesis, the strong CP problem, and dark matter</b>." It is a rather short paper which contains an existence proof that weakly coupled high-scale physics can explain phenomenological shortcomings of the SM <i>without introducing a naturalness problem</i>. The model adds only three right-handed neutrinos, a scalar doublet, and a scalar singlet to the SM. It contains a hierarchy of scales up to $\sim 10^{11}\text{ GeV}$. Nevertheless, corrections to the Higgs mass (and other mass scales) can be calculated, and it is shown that a technically natural decoupling limit of the model can protect all scales from large quantum corrections. If this is surprising in any way for you, since it is (or at least appears to be) a widely held misconception that high-scale physics implies a naturalness problem, then I suggest you read our preprint, or this <a href="http://syymmetries.blogspot.com.au/2015/08/friday-wrap-up-normal-ordering.html">earlier blog post</a>! Let's be clear here: the model does not solve the big hierarchy problem; we don't explain <i>where</i> the hierarchy of scales comes from, we just show that the hierarchy we introduce is not fine-tuned (that is the real worry), i.e. it is a radiatively stable hierarchy, or, it is "technically natural".<br />
<br />
I find it extremely interesting that the major shortcomings of the standard model can be answered naturally in such a modest extension of the SM. Models like this with weakly coupled high-scale physics, in my opinion, deserve more attention.<br /></div>
</div>
</li>
</ul>
<ul><ul></ul>
<li>The Taller de Altas Energías 2015 School is currently ongoing (<a href="http://benasque.org/2015tae/cgi-bin/talks/allprint.pl">programme here</a>).</li>
</ul>
<ul><ul></ul>
<li>Links without (too many) thinks:</li>
<ul>
<li>Life and Physics from Jon Butterworth: "How the Higgs boson is born and how it dies: the <a href="http://www.theguardian.com/science/life-and-physics/2015/sep/20/how-the-higgs-boson-is-born-and-how-it-dies-the-most-precise-picture-so-far">most precise picture</a> so far."</li>
<li>ATLAS Blogs: <a href="http://atlas.ch/blog/?p=3199">Part 2 of</a> James Howarth's TOP2015 review.</li>
<li>The Conversation: "How we plan to bring <a href="https://theconversation.com/how-we-plan-to-bring-dark-matter-to-light-46989">dark matter</a> to light," with a little on SUPL and SABRE.</li>
<li>Cosmos: "Ghost traps: <a href="https://cosmosmagazine.com/physical-sciences/ghost-traps-hunt-dark-matter">the hunt</a> for dark matter," interesting to read if only to observe how the field's "dark matter = WIMP" prejudice leads to misleading (even incorrect) statements in lay articles...</li>
</ul>
</ul>
<ul>
<li>In video/audio media:</li>
<ul>
<li><a href="https://inparticular.web.cern.ch/content/ep-3-particle-zoo">In Particular</a> Ep 3: Particle Zoo... what is your favourite particle? [35:15]</li>
<li>CERN: Timelapse video of the <a href="https://youtu.be/XY2lFDXz8aQ">CERN Axion Solar Telescope</a> (CAST) following the Sun [1:22], and a bit of noise rock in situ; <a href="https://youtu.be/tZqQGbSnSTA">Deerhoof</a> vs. the Large Hadron Collider [9:05].</li>
<li>Waking Up with Sam Harris: The <a href="http://www.samharris.org/blog/item/the-multiverse-you-you-you-you">Multiverse & You</a> (& You & You & You…), A Conversation with Max Tegmark. [1:26:42]</li>
<li>MinutePhysics: Why do we put <a href="https://youtu.be/Ij-u2bHo_fw">telescopes in space</a>? [2:20]</li>
<li>It's Okay to be Smart: Theory vs. Hypothesis vs. Law... <a href="https://youtu.be/lqk3TKuGNBA">Explained</a>! [7:11]</li>
<li>Numberphile: <a href="https://youtu.be/vA2cdHLKYB8">Philosophy</a> of Numbers. [9:40]</li>
</ul>
</ul>
<ul>
<li>Can't get enough of these <a href="http://www.nasa.gov/feature/perplexing-pluto-new-snakeskin-image-and-more-from-new-horizons">high resolution images</a> of Pluto...<br /><br /><div class="separator" style="clear: both; text-align: center;">
<a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhE3p0j979qyk8Ebzt97lX7BVnjgcWbYQa1lIwe4geaR7eoXwWSWjpzXCgXsQyi8T07JSvCxLdnj36KEKY4Pkkzn3zTnmKqdL8Q4MSmftZot0BJ5ZFBa_zk_jcFJWkkcOo88jvH2w2nMaw/s1600/snakeskin_detail.png" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" height="246" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhE3p0j979qyk8Ebzt97lX7BVnjgcWbYQa1lIwe4geaR7eoXwWSWjpzXCgXsQyi8T07JSvCxLdnj36KEKY4Pkkzn3zTnmKqdL8Q4MSmftZot0BJ5ZFBa_zk_jcFJWkkcOo88jvH2w2nMaw/s400/snakeskin_detail.png" width="400" /></a></div>
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</li>
</ul>
Bluejayhttp://www.blogger.com/profile/06935684943024856641noreply@blogger.com1tag:blogger.com,1999:blog-959149188511266512.post-62224022148835479752015-09-18T11:23:00.002+10:002015-09-18T11:25:18.778+10:00Friday wrap-up: diboson update, XMASS...Wherein I list some (mostly) recent happenings, ramble a bit, and provide links, in an order roughly determined by importance and relevance to particle physics. Views are my own. Content very definitely skewed by my own leanings and by papers getting coverage, and it may not even be correct. It is a blog after all...<br />
<br />
<ul>
<li>It's the season for conferences! This week we have...</li>
<ul>
<li>8th International Workshop on Top Quark Physics (TOP2015: <a href="http://indico.cern.ch/event/351006/timetable/#20150914.detailed">indico</a>; <a href="https://twitter.com/TopQuark2015">twitter</a>). One of the interesting new results includes <a href="http://cds.cern.ch/record/2052585">evidence for</a> (>3σ) single top quark production in the s-channel with the 8 TeV dataset. There's an entertaining review of the <a href="http://atlas.ch/blog/?p=3183">first two days here</a> from James Howarth.</li>
<li>Particle Astrophysics and Cosmology Including Fundamental InteraCtions (PACIFIC 2015: <a href="https://hepconf.physics.ucla.edu/pacific/agenda.html">agenda</a>).</li>
<li>Corfu Summer Institute: 15th Hellenic School and Workshops on Elementary Particle Physics and Gravity (<a href="http://www.physics.ntua.gr/corfu2015/programme.html">programme</a>).</li>
</ul>
</ul>
<ul>
<li>A couple of interesting conf-notes out this week as well. The first is the ATLAS/CMS <a href="http://cds.cern.ch/record/2052583">combined Higgs results</a> we saw presented a <a href="http://syymmetries.blogspot.com.au/2015/09/friday-wrap-up-atlascms-higgs.html">couple of weeks ago</a>.</li>
</ul>
<ul>
<li>The second is an ATLAS diboson resonance search which <a href="http://cds.cern.ch/record/2052583">combines the results</a> from the large-R dijet channel with the leptonic channels. The results are well summed up by the first Figure in the Appendix:<br /><div class="separator" style="clear: both; text-align: center;">
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<div class="separator" style="clear: both; text-align: center;">
<a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgRDRyrrONjKZAZmmA8mMQVOpSjhVRGFzIe7kY1qtLcEhWawGJit5QkKkQo9hvkJ_md9Vaj1ALAvQsEqZf23-Uy0TouYBjCr0vB342f08jZkmk5UsH4ku7GouCAswOCodfTgAn-1iaztJk/s1600/Screenshot+from+2015-09-18+10%253A27%253A28.png" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" height="271" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgRDRyrrONjKZAZmmA8mMQVOpSjhVRGFzIe7kY1qtLcEhWawGJit5QkKkQo9hvkJ_md9Vaj1ALAvQsEqZf23-Uy0TouYBjCr0vB342f08jZkmk5UsH4ku7GouCAswOCodfTgAn-1iaztJk/s400/Screenshot+from+2015-09-18+10%253A27%253A28.png" width="400" /></a></div>
<br />In short, when interpreted as a $W'$ resonance decaying to $WZ$, they see a 3.4σ local excess in the boosted jet topology and absolutely nothing in the leptonic channels. As well, these leptonic channels were sensitive to the $W'$ interpretation of the dijet excess, so that the local significance when combined falls to 2.5σ. Taken at face value then, if the dijet excess is really new physics, it is unlikely to be as simple as $W'\to WZ$. [As an aside: I do wonder how the community's reaction would have differed if <i>this</i> were that paper that was published first?]. To mimic such a signal without the leptons you would need a heavy resonance decaying to two exotic particles with mass $\sim m_Z$, which then decay mostly to quarks... would be difficult to hide these low mass exotics. Or else it is something more complex that happens to pass the selection criteria for the fat jet analysis but produces very few isolated leptons. Anyway, there have been <a href="http://inspirehep.net/search?ln=en&p=refersto%3Arecid%3A1374218">>30 extra citations</a> to the original ATLAS paper since I made a <a href="http://syymmetries.blogspot.com.au/2015/07/friday-wrap-up-diboson-excess-eps-hep.html">quick literature survey</a> seven weeks ago, and more every week. For me it seems sensible to just wait and see what the new data says (probably some time next year), happy to watch the ambulance in the distance, starting to speed up...</li>
</ul>
<ul>
<li>The TAUP2015 <a href="http://taup2015.to.infn.it/scientific-program/parallel-sessions/">parallel session slides</a> are now up. Indeed, as speculated last week, XMASS has a best fit modulation that is opposite in phase to that seen by DAMA/LIBRA (see <a href="http://www.taup-conference.to.infn.it/2015/day2/parallel/dma/3_kobayashi.pdf">Slide 10 [pdf]</a>). It is enough evidence to exclude much of the region where the DAMA signal can be interpreted as a standard WIMP with spin-independent nucleon scattering cross-section (though this is nothing new). Interesting to see what their results will be in the fiducial volume (analysis ongoing).<br /><br /><div class="separator" style="clear: both; text-align: center;">
<a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhlemuuh3tNLUrsqZU2zj17yYnghz8M7tkvH6T8XCkGR4J03qLGHaKYnfpXMhI0up1DnAoeN7BS6v6F2Cu06vlogQ-OHwEvBvUrp4g6aV_PiMVefSnTdbl-q54dV7DbUTAAI0U7HgJsH6s/s1600/Untitled.png" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" height="295" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhlemuuh3tNLUrsqZU2zj17yYnghz8M7tkvH6T8XCkGR4J03qLGHaKYnfpXMhI0up1DnAoeN7BS6v6F2Cu06vlogQ-OHwEvBvUrp4g6aV_PiMVefSnTdbl-q54dV7DbUTAAI0U7HgJsH6s/s400/Untitled.png" width="400" /></a></div>
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</li>
<li>32 Australian institutions <a href="https://www.science.org.au/SAGE/Pilot">have signed up to</a> the Science in Australia Gender Equity (SAGE) pilot: "Commencing in September 2015, the pilot requires participants to collect, analyse and present data on gender equity policies and practices in STEM departments, as well as identify gaps and opportunities for improvement."</li>
</ul>
<ul>
<li>Links without thinks:</li>
<ul>
<li>Institute for Advanced Study: "Beyond the Higgs: From the <a href="https://www.ias.edu/ias-letter/2015/arkani-hamed-collider">LHC to China</a>."</li>
<li>Richard Dawid wrote a guest blog on the reference frame: "<a href="http://motls.blogspot.com.au/2015/09/what-confirms-physical-theory.html">What confirms</a> a physical theory?" This should be taken in the context of that Ellis/Silk <a href="http://www.nature.com/news/scientific-method-defend-the-integrity-of-physics-1.16535">nature comment article</a> and the <a href="http://syymmetries.blogspot.com.au/search/label/Dawid">ensuing debate</a> on post-empirical science.</li>
<li>New Scientist: "Black holes may be <a href="https://www.newscientist.com/article/dn28159-black-holes-may-be-brick-walls-that-bounce-information-back-out/">brick walls</a> that bounce information back out." On 't Hooft's <a href="http://arxiv.org/abs/1509.01695">new contribution</a> to the black hole information paradox...</li>
<li>... and Sabine Hossenfelder's reaction at Starts With a Bang: "Black holes and <a href="https://medium.com/starts-with-a-bang/black-holes-and-academic-walls-ef9add7e6a3a">academic walls</a>."</li>
<li>Also at Starts With a Bang: "Will The LHC Be <a href="https://medium.com/starts-with-a-bang/will-the-lhc-be-the-end-of-experimental-particle-physics-bf69355df75f">The End Of</a> Experimental Particle Physics?"</li>
</ul>
</ul>
<ul>
<li>In video/audio media:</li>
<ul>
<li>CERN: A <a href="https://youtu.be/JTLrwWLrYJk">superfast chip</a> for particle detection. [3:34]</li>
<li>MinutePhysics: Why It's Impossible to <a href="https://youtu.be/1Hqm0dYKUx4">Tune a Piano</a>. [4:19]</li>
<li>Vi Hart: <a href="https://youtu.be/BEz-vGJvaik">Infinite Trees</a> Are Super Weird. [6:18]</li>
<li>Numberphile: <a href="https://youtu.be/NWBToaXK5T0">Langton's Ant</a>. [4:28]</li>
</ul>
</ul>
<ul>
<li>Lastly, in images from space, it is hard to top these <a href="http://www.nasa.gov/feature/pluto-wows-in-spectacular-new-backlit-panorama">new images</a> of Pluto!<br /><br /><div class="separator" style="clear: both; text-align: center;">
<a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhJ8SsA1QM1hyphenhyphenucAGSqMGb03Mg-Gup6R5Id1fwIDAKfdlKB1qvCyj6_eTJo9e4hF35zyRFu5qgYkwwU0Fj3E7hP-8d3J7r7YEtRhO4HK018JJLzfq5KIHCt3QTP8LkoSd6jDL8QA-wcdaY/s1600/nh-apluto-mountains-plains-9-17-15_0.png" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" height="256" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhJ8SsA1QM1hyphenhyphenucAGSqMGb03Mg-Gup6R5Id1fwIDAKfdlKB1qvCyj6_eTJo9e4hF35zyRFu5qgYkwwU0Fj3E7hP-8d3J7r7YEtRhO4HK018JJLzfq5KIHCt3QTP8LkoSd6jDL8QA-wcdaY/s400/nh-apluto-mountains-plains-9-17-15_0.png" width="400" /></a></div>
<div style="text-align: center;">
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</li>
</ul>
Bluejayhttp://www.blogger.com/profile/06935684943024856641noreply@blogger.com0tag:blogger.com,1999:blog-959149188511266512.post-38437643823209384512015-09-12T10:15:00.000+10:002015-09-16T12:37:03.955+10:00Friday wrap-up: XMASS, multi-component dark matter...Wherein I list some (mostly) recent happenings, ramble a bit, and provide links, in an order roughly determined by importance and relevance to particle physics. Views are my own. Content very definitely skewed by my own leanings and by papers getting coverage, and it may not even be correct. It is a blog after all...<br />
<br />
<ul>
<li>The XIV International Conference on Topics in Astroparticle and Underground Physics (TAUP 2015) conference has been happening this week (<a href="https://twitter.com/hashtag/taup15?f=tweets&vertical=default&src=hash">hashtag here</a>). The <a href="http://taup2015.to.infn.it/scientific-program/plenary-talks/">plenary talks</a> are available but unfortunately a very many interesting parallel sessions are inaccessible...</li>
</ul>
<ul>
<li>One of those parallel sessions included a preliminary new result of the search for an annual modulation signal at XMASS. A summary and some plots can be found in <a href="http://www-sk.icrr.u-tokyo.ac.jp/xmass/whatsnew/whatsnew-20150907-e.pdf">this document [pdf]</a>. They see "a weak modulation effect" which they say can be explained by a modest fluctuation background fluctuation, i.e., not significant results. Such are the difficulties in searching for annual modulation in only ~1.5yrs of data. No quote of the phase, but the fit for the modulation in their Figure 1 (below) has a negative amplitude, which might suggest that the best fit phase is ~6 months displaced from the standard halo model maximum in June... anyone have more information?<br /><br /><div class="separator" style="clear: both; text-align: center;">
<a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhIY86fIezAYgvmUrC3LWSRK5g2PfEQnt-tGM1SzqK5RaqWhA5IhWcM_TtyoA6T03FyyEmlkZsfmk_IPNkzdX7dTxUHzJBsaC4Gjz3JU3a1uK33AbwNKhYTjugNd99Pw_NeBWNZjxjB-Jg/s1600/Screenshot+from+2015-09-11+13%253A41%253A07.png" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" height="256" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhIY86fIezAYgvmUrC3LWSRK5g2PfEQnt-tGM1SzqK5RaqWhA5IhWcM_TtyoA6T03FyyEmlkZsfmk_IPNkzdX7dTxUHzJBsaC4Gjz3JU3a1uK33AbwNKhYTjugNd99Pw_NeBWNZjxjB-Jg/s400/Screenshot+from+2015-09-11+13%253A41%253A07.png" width="400" /></a></div>
<div style="text-align: center;">
<br /></div>
</li>
</ul>
<ul>
<li>Robert Foot here in Melbourne maintains that it is still possible that dark matter could be the explanation for annual modulation signals seen by DAMA/LIBRA, CoGeNT, and <a href="http://syymmetries.blogspot.com.au/2015/07/friday-wrap-up-diboson-excess-eps-hep.html">recently by XENON100</a> (and now perhaps XMASS?). He posted <a href="http://arxiv.org/abs/1508.07402">to the arXiv</a> last week outlining a scenario... <br /><br />The possible explanation is predicated on a dark matter halo made up of a pressure supported multi-component self-interacting plasma. Considering the mirror dark matter model for definiteness, the halo is mostly made up of dark electrons and dark He ions. There is a (massless) dark photon which mixes with the SM photon, imbuing the dark matter with dark charge and SM nanocharge. Far from the Earth the plasma is in thermal equilibrium; turns out this naively implies a ~100 times larger flux of dark electrons incident on the Earth than dark He. However, dark matter will be captured within the Earth, and by contradiction one can argue that dark electromagnetic fields must arise to equilibrate the (charge weighted) flux of dark electrons and dark He. The flux of the dark electrons on the Earth's surface, which can be possibly detected in direct detection experiments via single electron scattering, then depends on the details of these dark fields, which are assumed to arise from bulk movement of the charged dark matter on/near the surface of the captured dark matter sphere. Since the flux annually modulates due to the motion of the Earth relative to the halo, then so will these dark fields, and so will the electron flux incident on the Earth's surface. Needless to say, determining the flux is a very thorny dynamical problem... the preprint presents a "somewhat primitive" analysis to show in principal that such physics can give a large annual modulation fraction (which is a function of latitude). The "smoking gun" (and the make-or-break) for this scenario is a large <a href="http://arxiv.org/abs/1412.0762">diurnal (daily) modulation</a>.<br /><br />This just goes to highlight the obvious fact that direct detection results are not as simple as comparing exclusion curves in spin-independent nucleon scattering cross section versus mass.</li>
</ul>
<ul>
<li>Further on the direct detection front, Lateral Mag <a href="http://www.lateralmag.com/issue-2-underground/mining-for-wimps-the-subterranean-search-for-dark-matter">have a story</a> on the dark matter direct detection project getting underway here in Australia, in the Stawell Underground Physics Laboratory (SUPL). Funding for the lab has been obtained, and construction should start early next year!</li>
</ul>
<ul>
<li>On this blog:</li>
</ul>
<ul><ul>
<li>I have <a href="http://syymmetries.blogspot.com.au/2015/08/friday-wrap-up-normal-ordering.html">updated my thoughts</a> on the hierarchy/naturalness problem from a month ago. I wanted to distinguish between a hierarchy problem and a naturalness problem; it is my opinion that these terms are used too loosely in modern hep parlance (and perhaps people have different definitions anyway), and this causes confusion (especially from the point of view of an impressionable PhD student). So... <br /><br />At least to me, the following definitions make sense: a <b>hierarchy problem</b> is an unexplained hierarchy of scales within a model, and; a <b>naturalness problem</b> (for a mass parameter) arises when a scale receives very large and physically meaningful quantum corrections. The SM+gravity suffers a hierarchy problem by definition, but it is not clear to me that this implies a naturalness problem for the electroweak scale. That is what I <a href="http://syymmetries.blogspot.com.au/2015/08/friday-wrap-up-normal-ordering.html">blogged about</a> a month ago. Actually, taken this way, minimal supersymmetry alone <i>doesn't</i> solve the hierarchy problem (i.e. it has a <a href="https://en.wikipedia.org/wiki/Mu_problem">mu problem</a>). Nevertheless (and if it arises at the TeV scale) supersymmetry ensures that the electroweak scale does not have a naturalness problem <i>whatever</i> the theory of gravity, and <i>whatever</i> scales are introduced in between (such as a GUT scale), which is in my opinion a very nice property and an admirable achievement for such models.</li>
</ul>
</ul>
<ul><ul>
<li>Playing with google charts recently I added a geomap and new/returning pageview charts using google analytics tracking, the <a href="https://developers.google.com/analytics/solutions/google-analytics-super-proxy">google analytics superproxy</a>, and a little javascript withquerying. They're a little messy right now but the information is there; the blog is getting >500 views a week now, so thanks for reading!</li>
</ul>
</ul>
<ul>
<li>Links without thinks:</li>
<ul>
<li>Backreaction: <a href="http://backreaction.blogspot.com.au/2015/09/macro-dark-matter.html">Macro dark matter</a>.</li>
<li>Lawrence Krauss via New Yorker: All scientists should be <a href="http://www.newyorker.com/news/news-desk/all-scientists-should-be-militant-atheists">militant atheists</a>.</li>
<li><a href="http://thelegacyproject.co.za/499-peter-jenni-interview-an-experimental-particle-physicist/">Legacy Project</a>: Peter Jenni (former ATLAS spokesperson).</li>
<li>Quanta: <a href="https://www.quantamagazine.org/20150910-einstein-insanity/">Einstein’s Parable</a> of Quantum Insanity.</li>
<li>Quanta: A <a href="https://www.quantamagazine.org/20150908-quantum-safe-encryption/">Tricky Path</a> to Quantum-Safe Encryption.</li>
</ul>
</ul>
<ul>
<li>In video/audio media:</li>
<ul>
<li>CERN: Innovative <a href="https://youtu.be/miJbB9MTwzU">cooling system</a> for silicon detectors. [3:35]</li>
<li>Frank Wilczek via bigthink: How <a href="http://bigthink.com/videos/frank-wilczek-on-einstein">Einstein changed</a> the way we see everything. [3:22]</li>
<li>Sixty Symbols: <a href="https://youtu.be/CH880_VrxxU">Hydrogen alpha</a>. [8:30]</li>
<li>Numberphile: numbers and <a href="https://youtu.be/PFkZGpN4wmM">free will</a> [15:02]; the <a href="https://youtu.be/BBp0bEczCNg">infinitesimal monad</a> [7:10], and; the <a href="https://youtu.be/WYijIV5JrKg">opposite of</a> infinity [15:04].</li>
<li>Objectivity: Magnets and <a href="https://youtu.be/MvxVlcsWuHE">black holes</a>. [5:45]</li>
</ul>
</ul>
<ul>
<li>News from space...</li>
</ul>
<ul><ul>
<li>A detailed <a href="http://www.jpl.nasa.gov/news/news.php?feature=4714">image of</a> the bright spot on Ceres...<br /><br /><div class="separator" style="clear: both; text-align: center;">
<a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgcDfSKG3ys_xw4I0H-0GL_TNzbC-scAU2-yXqdYXqXgwBdv7g5_rTZ8X6itzAShdaDIRfs18kNiY1HWudhxgWONtyJFNxZ8G6c8XH0r84aiBtpUQCMku5klVhxIDVw4sgi42OmC22-BuM/s1600/PIA19889-16.jpg" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" height="225" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgcDfSKG3ys_xw4I0H-0GL_TNzbC-scAU2-yXqdYXqXgwBdv7g5_rTZ8X6itzAShdaDIRfs18kNiY1HWudhxgWONtyJFNxZ8G6c8XH0r84aiBtpUQCMku5klVhxIDVw4sgi42OmC22-BuM/s400/PIA19889-16.jpg" width="400" /></a></div>
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<br /></div>
</li>
<li>... and incredible <a href="http://www.nasa.gov/feature/new-pluto-images-from-nasa-s-new-horizons-it-s-complicated">new images</a> of Pluto and Charon!<br /><br /><div class="separator" style="clear: both; text-align: center;">
<a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgvVr0ijd45LN74yMfWnEUMXo0Y3fCSr99AuDhMumHtqcUVC-Q9mxbmpLA1YrgDa1by4sCJyVfoHf0SmXL5p4TRBwITOmbJthc6myGhP8gr_z7DhGKN_mHDVNTQCVAWySFtwVSoaALM4jM/s1600/nh-spherical-mosaic-9-10-15.jpg" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" height="258" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgvVr0ijd45LN74yMfWnEUMXo0Y3fCSr99AuDhMumHtqcUVC-Q9mxbmpLA1YrgDa1by4sCJyVfoHf0SmXL5p4TRBwITOmbJthc6myGhP8gr_z7DhGKN_mHDVNTQCVAWySFtwVSoaALM4jM/s400/nh-spherical-mosaic-9-10-15.jpg" width="400" /></a></div>
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</li>
</ul>
</ul>
Bluejayhttp://www.blogger.com/profile/06935684943024856641noreply@blogger.com0tag:blogger.com,1999:blog-959149188511266512.post-37446838978308287952015-09-05T12:52:00.000+10:002015-09-05T12:52:29.072+10:00Friday wrap-up: ATLAS+CMS Higgs combination, THE rankings...Wherein I list some (mostly) recent happenings, ramble a bit, and provide links, in an order roughly determined by importance and relevance to particle physics. Views are my own. Content very definitely skewed by my own leanings and by papers getting coverage, and it may not even be correct. It is a blog after all...<br />
<br />
<ul>
<li>Conferences of interest this week include The 3rd Annual Large Hadron Collider Physics Conference (LHCP2015; <a href="https://indico.cern.ch/event/389531/timetable/#20150831.detailed">indico</a>; <a href="https://twitter.com/lhcp2015">twitter</a>), and QCD@LHC 2015 (<a href="https://indico.cern.ch/event/381832/timetable/#20150901.detailed">indico</a>).</li>
</ul>
<ul>
<li>At LHCP, Marco Pieri presented the brand new ATLAS+CMS Higgs combination (<a href="https://indico.cern.ch/event/389531/session/31/contribution/51/attachments/1147368/1645481/LHCHCP_MarcoPieri_fin.pdf">talk here [pdf]</a>). Slides 17 and 18 tell the story for the SM Higgs versus the null:<br /><br /><div class="separator" style="clear: both; text-align: center;">
<a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgArTJbuBWJb3Ui98b89vstbiNcIvNTK6AhQpLZtNaS5uBPaZBXRnVCNhfU0r22b3fTi77fZokrjh6adhWswrwotLkKXJXs-ISGTUY1Ilmkersek8oDVY_ziXHE3mQDO6YjmvYYUUZqmro/s1600/Untitled1.png" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" height="300" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgArTJbuBWJb3Ui98b89vstbiNcIvNTK6AhQpLZtNaS5uBPaZBXRnVCNhfU0r22b3fTi77fZokrjh6adhWswrwotLkKXJXs-ISGTUY1Ilmkersek8oDVY_ziXHE3mQDO6YjmvYYUUZqmro/s400/Untitled1.png" width="400" /></a></div>
<div class="separator" style="clear: both; text-align: center;">
<a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEiJSLAqNi9Tqvod5-HTiYQh43TQsfEr65tE3b2nI7ORzVu7vWPHxeepKV3W-C4x9LfCKeLvCirSfz5pMrvoc_s1WcCAs8rktpMLwM9u0h1z-L4qCNBRvOjlnkKeoU1CcPrjtFOrMYiOK3g/s1600/Untitled.png" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" height="300" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEiJSLAqNi9Tqvod5-HTiYQh43TQsfEr65tE3b2nI7ORzVu7vWPHxeepKV3W-C4x9LfCKeLvCirSfz5pMrvoc_s1WcCAs8rktpMLwM9u0h1z-L4qCNBRvOjlnkKeoU1CcPrjtFOrMYiOK3g/s400/Untitled.png" width="400" /></a></div>
<div style="text-align: center;">
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The interesting things for me are: global signal strength fit is $\mu=1.09^{+0.11}_{-0.10}$, H→ττ and VBF production are (preliminarily) "discovered" at >5σ, and ttH has a mild (2.3σ) excess (already hinted <a href="http://syymmetries.blogspot.com.au/2015/03/friday-wrap-up-higgs-mass-combination.html">at Moriond</a>) to keep an eye on. Different parameterisations are also studied, finding, of course, everything consistent with a SM Higgs. Would imagine we can look forward to the arXiv paper soon.</li>
</ul>
<ul>
<li>The Times Higher Education World University Rankings <a href="https://www.timeshighereducation.co.uk/blog/world-university-rankings-blog-dealing-freak-research-papers">have decided to exclude</a> from their analysis all papers with more than 1000 authors for the 2015-16 rankings. This obviously has a big impact on those involved in the ATLAS/CMS collaborations. Interesting to read the comments below the post from John Ellis, James Stirling, and Andrew Hamilton, among others.</li>
</ul>
<ul>
<li>According to <a href="http://www.nature.com/news/space-station-dark-matter-experiment-hits-a-glitch-1.18280">this nature news</a> article, there are some concerns for the cooling pumps in the AMS-02 experiment. There were originally four cooling pumps. They write: "Only one pump is needed at any given time. One failed in February 2014 and at least one of the other three is showing possible signs of trouble." Also: "[Ting] exhibited little patience for questions about the cooling pumps. 'We have four pumps — we only need one,' he says. 'We expect to operate for the lifetime of the space station.'"</li>
</ul>
<ul>
<li>Some movement on the Hawking/Perry/Strominger proposal for the black hole information loss problem. There's now a short stake-claiming <a href="http://arxiv.org/abs/1509.01147">arXiv paper</a>, and an hour-long talk from Malcolm Perry <a href="https://youtu.be/p1k3XKfl0CQ">on YouTube</a>. Sabine Hossenfelder <a href="http://backreaction.blogspot.com.au/2015/09/more-about-hawking-and-perrys-new.html">reacts here</a>.</li>
</ul>
<ul>
<li>From CERN: <a href="http://home.web.cern.ch/cern-people/updates/2015/08/lhc-run-2-reaching-top-learning-curve">a summary</a> on LHC Run 2 so far from Rolf Heuer (he comments on the CMS magnet: "... it’s clear that there are contaminants in the cold box that supplies the magnet with liquid helium, and this will therefore need a thorough clean.... All being well, CMS will be able to take data satisfactorily with field on until the end of the 2015 physics programme, postponing the cleaning operation until the winter stop in order to be ready for the start of 2016."), and a summary on <a href="http://home.web.cern.ch/scientists/updates/2015/09/out-clouds">recent scrubbing</a> runs.</li>
</ul>
<ul>
<li>Links without thinks:</li>
<ul>
<li><a href="https://www.reddit.com/r/IAmA/comments/3iuf6c/we_are_the_international_group_of_theoretical/">Reddit AMA</a> with a subset of the theoretical physicists who gathered for the Hawking Radiation Conference in Stockholm last week.</li>
<li>Quanta: <a href="https://www.quantamagazine.org/20150828-john-conway-a-life-in-games/">John Conway</a>, a life in games.</li>
<li>BackReaction: <a href="http://backreaction.blogspot.com.au/2015/09/loops-and-strings-and-stuff.html">Loops and Strings and Stuff</a>.</li>
</ul>
</ul>
<ul>
<li>In video/audio media:</li>
<ul>
<li>Fermilab: "Why I love neutrinos," from <a href="https://youtu.be/abx_vi9qeQM">M. Marshak</a>, <a href="https://youtu.be/FC_7sfnLVdc">A. Rubbia</a>, and <a href="https://youtu.be/OR6yGSpnj4Y">K. Scholberg</a>. [~1:00 each]</li>
<li><a href="https://youtu.be/rT4HG_Z8-9w">NA62</a>: chasing kaons. [2:32]</li>
<li>Alan Guth's <a href="http://videolectures.net/single_guth_multiverse/">public lecture</a> from Lepton-Photon: Inflationary Cosmology: Is Our Universe part of a Multiverse? [1:21:50]</li>
</ul>
</ul>
<ul>
<li>Lastly, here is <a href="http://www.nature.com/articles/srep13945">an antineutrino global map</a>: an experimentally informed model of Earth’s surface antineutrino flux over the 0 to 11 MeV energy spectrum.<br /><div style="text-align: center;">
<br /></div>
<div style="text-align: center;">
<a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEiHohr6lLSUwFyhZcyBKuNFACw1Nc8Uk1ojudb25VGrqYxnhUjVLKKxlQf1qmA4bUSLRq-ZTbjellZBtWzjWtJXELWqCLNIXoiP7NtRHzJi3-9tmgNJ-VZpAL6CuDViJDsDiZ9Wrt7KuOk/s1600/srep13945-f1.jpg" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" height="247" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEiHohr6lLSUwFyhZcyBKuNFACw1Nc8Uk1ojudb25VGrqYxnhUjVLKKxlQf1qmA4bUSLRq-ZTbjellZBtWzjWtJXELWqCLNIXoiP7NtRHzJi3-9tmgNJ-VZpAL6CuDViJDsDiZ9Wrt7KuOk/s400/srep13945-f1.jpg" width="400" /></a></div>
</li>
</ul>
Bluejayhttp://www.blogger.com/profile/06935684943024856641noreply@blogger.com0tag:blogger.com,1999:blog-959149188511266512.post-71601866306808388772015-08-28T11:27:00.000+10:002015-08-28T11:27:34.331+10:00Friday wrap-up: 3.5 keV line, SUSY2015, Hawking...Wherein I list some (mostly) recent happenings, ramble a bit, and provide links, in an order roughly determined by importance and relevance to particle physics. Views are my own. Content very definitely skewed by my own leanings and by papers getting coverage, and it may not even be correct. It is a blog after all...<br /><br />
<ul>
<li>The 3.5 keV "bulbulon" line <a href="http://arxiv.org/abs/1508.05186">strikes back</a>. [See this Nov 2014 <a href="http://resonaances.blogspot.com.au/2014/11/update-on-bananas.html">Résonaances post</a> for context].</li>
</ul>
<ul>
<li>The 23rd International Conference on Supersymmetry and Unification of Fundamental Interactions (SUSY2015; <a href="https://indico.cern.ch/event/331032/timetable/#20150825.detailed">indico</a>; <a href="https://twitter.com/hashtag/susy2015?f=tweets&vertical=default&src=hash">hashtag</a>) and 4th International Conference on New Frontiers in Physics (ICNFP2015; <a href="http://indico.cern.ch/event/344173/timetable/#20150824.detailed">indico</a>; <a href="https://twitter.com/hashtag/icnfp2015?f=tweets&vertical=default&src=hash">hashtag</a>) have been going this week.</li>
</ul>
<ul>
<li>Plenty of hype on a <a href="https://www.kth.se/en/aktuellt/nyheter/hawking-offers-new-solution-to-black-hole-mystery-1.586546">proposed solution</a> to the black hole information paradox from Stephen Hawking, Malcolm Perry, and Andrew Strominger: <a href="http://backreaction.blogspot.com.au/2015/08/hawking-proposes-new-idea-for-how.html">Backreaction</a>, <a href="http://www.scientificamerican.com/article/stephen-hawking-hasn-t-solved-the-black-hole-paradox-just-yet/">Scientific American</a>, <a href="https://www.newscientist.com/article/dn28090-stephen-hawking-says-he-has-a-way-to-escape-from-a-black-hole/?">New Scientist</a>...</li>
</ul>
<ul>
<li>Links without thinks:</li>
<ul>
<li><a href="http://www.sciencedirect.com/science/article/pii/S0262407915310319">Strangely Familiar</a>: dark matter as many-quark states, from Sabine Hossenfelder and Naomi Lubick via New Scientist.</li>
<li>The <a href="http://www.scientificamerican.com/magazine/sa/2015/09-01/">current issue</a> of Scientific American is a special issue on Einstein. [You should be able to access the articles through a University subscription].</li>
</ul>
</ul>
<ul>
<li>In video/audio media:</li>
<ul>
<li><a href="http://www.partiallyderivative.com/news/2015/8/26/episode-33-data-of-the-impossible">Partially Derivative</a>: Data of the Impossible, with Kyle Cranmer and Lee Smolin.</li>
<li><a href="http://www.equaltimeforfreethought.org/2015/08/22/show-538-%E2%80%9Cpeer-reviewed%E2%80%9D-wsabine-hossenfelder/">Equal Time for Freethought</a>: Sabine Hossenfelder on peer review.</li>
<li><a href="https://youtu.be/LVXj5hRyP8s">SLAC</a>: Plasma Wakefield Acceleration with Positrons.</li>
</ul>
</ul>
<ul>
<li>This <a href="http://www.nasa.gov/jpl/dawn-sends-sharper-scenes-from-ceres">6 km tall</a> mountain on Ceres is a <a href="http://www.slate.com/blogs/bad_astronomy/2015/08/26/ceres_weird_mountain_stands_tall.html">bit of a mystery</a>!<br /><br /><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgetsib1DSFRMiZm_lrSbwRslgWCV5Zzw7U4sYc0UNf6hyLfBjvLd4zLmhpCvGk8ha8h2AJWq8GUrX_HxmF71HKhzRLi7EyqqEHYJmzxGrrwMFZel_Vv3LWXfpt7ART7ArekM7PE0-bhEw/s1600/pia19631.jpg" imageanchor="1" style="margin-left: 1em; margin-right: 1em; text-align: center;"><img border="0" height="225" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgetsib1DSFRMiZm_lrSbwRslgWCV5Zzw7U4sYc0UNf6hyLfBjvLd4zLmhpCvGk8ha8h2AJWq8GUrX_HxmF71HKhzRLi7EyqqEHYJmzxGrrwMFZel_Vv3LWXfpt7ART7ArekM7PE0-bhEw/s400/pia19631.jpg" width="400" /></a></li>
</ul>
Bluejayhttp://www.blogger.com/profile/06935684943024856641noreply@blogger.com0tag:blogger.com,1999:blog-959149188511266512.post-68584009168566435882015-08-21T16:04:00.001+10:002015-08-21T16:04:25.389+10:00Friday wrap-up: 3/fb, ATLAS on Higgs LFV decays...Wherein I list some (mostly) recent happenings, ramble a bit, and provide links, in an order roughly determined by importance and relevance to particle physics. Views are my own. Content very definitely skewed by my own leanings and by papers getting coverage, and it may not even be correct. It is a blog after all...<br />
<br />
FYI, I've posted a list of recommended (active) high energy physics news and blog links in the sidebar, also here for those using a reader: <a href="http://perfectpuddle.blogspot.com.au/">A Perfectly Formed Puddle</a>,
<a href="http://www.science20.com/quantum_diaries_survivor">A Quantum Diaries Survivor</a>,
<a href="http://atlas.ch/blog/">ATLAS Blog</a>,
<a href="http://atlas-physics-updates.web.cern.ch/atlas-physics-updates/">ATLAS Briefings</a>,
<a href="http://atlas.ch/news/">ATLAS News</a>,
<a href="http://backreaction.blogspot.com.au/">Backreaction</a>, <a href="http://press.web.cern.ch/press-releases">CERN Press Releases</a>, <a href="http://home.web.cern.ch/scientists/updates">CERN Updates</a>,
<a href="http://cylindricalonion.web.cern.ch/">CMS Blog: Cylindrical Onion</a>,
<a href="http://cms.web.cern.ch/news/category/382">CMS Physics News</a>,
<a href="https://muon.wordpress.com/">Collider Blog</a>,
<a href="http://www.ellipsix.net/blog/index.html">Ellipsix</a>,
<a href="http://www.interactions.org/cms/">Interactions.org</a>,
<a href="http://www.theguardian.com/science/life-and-physics">Life and Physics</a>,
<a href="http://latticeqcd.blogspot.com.au/">Life on the Lattice</a>,
<a href="http://axelmaas.blogspot.com.au/">Looking Inside the SM</a>,
<a href="http://nautil.us/term/f/Particle%20Physics">Nautilus: Particle Physics</a>,
<a href="http://neutrinoscience.blogspot.com.au/">Neutrino Blog</a>,
<a href="http://www.math.columbia.edu/~woit/wordpress/">Not Even Wrong</a>,
<a href="http://profmattstrassler.com/">Of Particular Significance</a>,
<a href="http://www.physicsmatt.com/blog/">PhysicsMatt</a>,
<a href="http://www.preposterousuniverse.com/blog/">Preposterous Universe</a>,
<a href="https://www.quantamagazine.org/category/physics-2/">Quanta Magazine: Physics</a>,
<a href="http://www.quantumdiaries.org/">Quantum Diaries</a>,
<a href="https://blog.rwth-aachen.de/particle-physics-theory/">RWTH Aachen</a>,
<a href="http://resonaances.blogspot.com.au/">Resonaances</a>,
<a href="http://betatim.github.io/">Tim Head</a>,
<a href="http://transcyberphysix.blogspot.com.au/">Transcyberphysix</a>,
<a href="http://www.symmetrymagazine.org/">symmetry magazine</a>,
<a href="http://motls.blogspot.com.au/">the reference frame</a>.<br />
<br />
<ul>
<li>The XXVII International Symposium on Lepton Photon Interactions at High Energies (Lepton Photon 2015) has been going this week (<a href="https://indico.cern.ch/event/325831/timetable/#20150817.detailed">indico</a>/<a href="https://twitter.com/LeptonPhoton15">twitter</a>). We heard <a href="http://indico.cern.ch/event/325831/session/0/contribution/7">from Mike Lamont</a> about LHC performance; multiple commissioning issues (electron cloud, UFOs, ULO, ...), none of which are expected to be long term, mean that predicted integrated luminosity for ATLAS/CMS in 2015 <b>is now at ~3/fb</b>. [See also a brief story at <a href="https://www.newscientist.com/article/dn28068-high-energy-lhc-plans-held-up-by-ufos-and-electron-clouds/">New Scientist</a>].</li>
</ul>
<ul>
<li>Following up the <a href="http://syymmetries.blogspot.com.au/2015/03/friday-wrap-up-higgs-lfv-decays-higgs.html">CMS 2.4σ excess</a> from February, ATLAS on Monday placed their search for LFV Higgs decays in the $\mu\tau_{had}$ channel <a href="http://arxiv.org/abs/1508.03372">on the arXiv</a>. Their result is consistent with zero, but also consistent with CMS. Their best fit is a $\mathcal{B}=(0.77\pm 0.62)\%$, compared to $\mathcal{B}=(0.84^{+0.39}_{-0.30})\%$ from CMS. One can see that the CMS search is more sensitive; this is likely driven by the fact that CMS also included the $\mu\tau_e$ channel. Do ATLAS have plans to look at this channel soon as well?</li>
</ul>
<ul>
<li>A few weeks ago <a href="http://syymmetries.blogspot.com.au/2015/07/friday-wrap-up-diboson-excess-eps-hep.html">we mentioned</a> that LHCb announced preliminary results in a search for displaced light scalar bosons. The preprint is <a href="http://arxiv.org/abs/1508.04094">on the arXiv</a> now, which allowed me to <a href="http://syymmetries.blogspot.com.au/2015/02/friday-wrap-up-leptogenesis-displaced.html">scrape their data points</a> and reinterpret their branching limits for the real singlet scalar portal. For interest, the result is below in orange, quite similar to the approximate plot from that previous blog post (more information there). Anyway, LHCb have done a great job excluding parameter space!<br /><br /><div class="separator" style="clear: both; text-align: center;">
<a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjthAZWkUrwaWd2erRr0nGBQv6VVYfkxALMNHVHEZqct23AxYD5wTF91OAmDK2F1kwv_KhANqiWXk2hbF677Y7ejGTpT93o-M41DuY08onQ65fX-X-KHD_boaY2rjLBIMuoAi_CICKOyRc/s1600/Screenshot+from+2015-08-21+14%253A12%253A00.png" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" height="243" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjthAZWkUrwaWd2erRr0nGBQv6VVYfkxALMNHVHEZqct23AxYD5wTF91OAmDK2F1kwv_KhANqiWXk2hbF677Y7ejGTpT93o-M41DuY08onQ65fX-X-KHD_boaY2rjLBIMuoAi_CICKOyRc/s400/Screenshot+from+2015-08-21+14%253A12%253A00.png" width="400" /></a></div>
<div style="text-align: center;">
<br /></div>
</li>
</ul>
<ul>
<li>The Dark Energy Survey (DES) has discovered eight new dwarf galaxy candidates (<a href="http://arxiv.org/abs/1508.03622">arXiv</a>/<a href="http://www.interactions.org/cms/?pid=1035046">press release</a>), to add to the nine they discovered <a href="http://syymmetries.blogspot.com.au/2015/03/friday-wrap-up-atlas-on-z-excess-cms.html">earlier this year</a>. The sky is filling with satellites...<br /><br /><div class="separator" style="clear: both; text-align: center;">
<a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgKeAVB6zP7VEfig-ijO7ujE2gqZiEzOrAkNm1C5iTq_M8_3boeArHFOj8ZdaoKAspJUe0M9b4zEYHRJnpcUH3aVSq929ZKNpYulp0u9GAHF3z_ky7XvaAFVFugP1Q4fHcppXpkL6rfSwE/s1600/Screenshot+from+2015-08-21+14%253A42%253A56.png" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" height="351" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgKeAVB6zP7VEfig-ijO7ujE2gqZiEzOrAkNm1C5iTq_M8_3boeArHFOj8ZdaoKAspJUe0M9b4zEYHRJnpcUH3aVSq929ZKNpYulp0u9GAHF3z_ky7XvaAFVFugP1Q4fHcppXpkL6rfSwE/s400/Screenshot+from+2015-08-21+14%253A42%253A56.png" width="400" /></a></div>
<div style="text-align: center;">
<br />
<div style="text-align: left;">
Now taking bets on which one has an excess of gamma rays consistent with dark matter annihilation... </div>
</div>
</li>
</ul>
<ul>
<li><div style="text-align: left;">
On that note, the first paper pointing out the <a href="http://syymmetries.blogspot.com.au/2015/03/friday-wrap-up-atlas-on-z-excess-cms.html">gamma ray excess</a> in Reticulum II (on the day of the first DES dwarf galaxy candidates announcement) <a href="http://syymmetries.blogspot.com.au/2015/03/friday-wrap-up-atlas-on-z-excess-cms.html">was published</a> in Physical Review Letters this week. Tracy Slatyer has a <a href="http://physics.aps.org/articles/v8/81">Viewpoint here</a>.</div>
</li>
</ul>
<ul>
<li><a href="https://www.quantamagazine.org/20150820-the-case-for-complex-dark-matter/">The case for complex dark matter</a>, at Quanta with James Bullock (of University of California, Irvine).</li>
</ul>
<ul>
<li><a href="http://backreaction.blogspot.com.au/2015/08/superfluid-dark-matter.html">Superfluid dark matter</a>, at Backreaction.</li>
</ul>
<ul>
<li>Mary K. Gaillard has a book out: <i>A Singularly Unfeminine Profession: One Woman's Journey in Physics</i>. There's a review on <a href="http://www.nature.com/nature/journal/v524/n7564/full/524160a.html">nature.com</a> from Val Gibson.</li>
</ul>
<ul>
<li>In video/audio media:</li>
<ul>
<li>US LHC: <a href="https://youtu.be/I96TIs0MAvU">How to make a discovery</a>. [3 minutes]</li>
<li>Fermilab: <a href="https://youtu.be/2LnGKdV30xg">Pentaquarks</a>. [9 minutes]</li>
<li>CERN: <a href="https://youtu.be/j7Lh0WAjx-o">The music of physics</a>. [3 minutes]</li>
</ul>
</ul>
<ul>
<li>For your enjoyment, here's a <a href="https://vimeo.com/136223988">Pluto flyby</a>...<br /><br /><iframe allowfullscreen="" frameborder="0" height="375" mozallowfullscreen="" src="https://player.vimeo.com/video/136223988" webkitallowfullscreen="" width="500"></iframe></li>
</ul>
Bluejayhttp://www.blogger.com/profile/06935684943024856641noreply@blogger.com0tag:blogger.com,1999:blog-959149188511266512.post-2500597347266518362015-08-14T20:41:00.002+10:002015-08-14T20:48:32.214+10:00Friday wrap-up: various links...Wherein I list some (mostly) recent happenings, ramble a bit, and provide links, in an order roughly determined by importance and relevance to particle physics. Views are my own. Content very definitely skewed by my own leanings and by papers getting coverage, and it may not even be correct. It is a blog after all..<br />
<br />
Slow news week, or maybe I was just too busy...?<br />
<ul>
<li>LHC is <a href="https://op-webtools.web.cern.ch/op-webtools/vistar/vistars.php">doing 13 TeV physics</a> again, now with 25ns bunch spacing.</li>
</ul>
<ul>
<li>The LHCb <a href="http://syymmetries.blogspot.com.au/2015/07/friday-wrap-up-diboson-excess-eps-hep.html">pentaquark</a> discovery has been published in PRL. There's a Viewpoint article from Kenneth Hicks <a href="http://physics.aps.org/articles/v8/77">here</a>.</li>
</ul>
<ul>
<li>The BOOST2015 7th International Workshop on Boosted Object Phenomenology was on this week (<a href="https://indico.cern.ch/event/382815/other-view?view=standard">indico</a>/<a href="https://twitter.com/hashtag/boost2015?f=tweets&vertical=default&src=hash">hashtag</a>).</li>
</ul>
<ul>
<li>The 43rd SLAC Summer Institute is going on at the moment: The Universe of Neutrinos (<a href="https://indico.cern.ch/event/373156/other-view?view=standard">indico</a>).</li>
</ul>
<ul>
<li>Blog post <a href="http://backreaction.blogspot.com.au/2015/08/dear-dr-bee-why-do-some-people-assume.html">at Backreaction</a>: Why do some people assume that the Planck length/time are the minimum possible length and time?</li>
</ul>
<ul>
<li>John Preskill <a href="http://quantumfrontiers.com/2015/08/09/kitaev-moore-read-share-dirac-medal/">muses on</a> Kitaev, Moore, and Read's shared ICTP Dirac Medal and anyons, the two-dimensional cousins to our fermions and bosons.</li>
</ul>
<ul>
<li>A couple of articles from Shannon Hall at Nautilus: <a href="http://nautil.us/blog/is-it-time-to-embrace-unverified-theories">Is It Time</a> to Embrace Unverified Theories? and; <a href="http://nautil.us/blog/6-graphs-that-showed-landmark-discoveriesbut-were-later-debunked">6 Graphs</a> That Showed Landmark Discoveries—but Were Later Debunked.</li>
</ul>
<ul>
<li>In video/audio media:</li>
<ul>
<li><a href="http://www.symmetrymovie.com/">Symmetry</a>, a dance-opera film, premiered this week; trailers at the link.</li>
<li><a href="http://www.dailymotion.com/video/x2za7v6_big-bang-aftershock_tv">Big Bang Aftershock</a>, on the BICEP2 discovery and fallout. [40 minutes]</li>
<li><a href="http://www.sbs.com.au/ondemand/video/491544131832/uranium-twisting-the-dragons-tail">Uranium</a>: Twisting the Dragon's Tail. Hosted by Derek from Veritasium, and researched by my officemate Rebecca Leane! [Link for Australians; 50 minutes]</li>
<li><a href="https://www.quantamagazine.org/20150813-how-does-symmetry-shape-natures-laws/">How Does</a> Symmetry Shape Nature’s Laws? from Quanta. [2 minutes]</li>
<li><a href="https://youtu.be/QAa2O_8wBUQ">What is</a> Dark Matter and Dark Energy? for laymen, from Nova Project. [6 minutes]</li>
<li><a href="https://youtu.be/WwRvWMRUhKE">What Has</a> New Horizons Taught Us About Pluto? at It's Okay to be Smart. [6 minutes]</li>
<li><a href="https://youtu.be/M-i9v9VfCrs">Prime knots</a> at Numberphile. [7 minutes]</li>
<li><a href="https://youtu.be/Inc9BtRip04">Tour Ceres</a>, from Nasa JPL. [2 minutes]</li>
</ul>
</ul>
<ul>
<li>On 13 Aug, Rosetta witnessed Comet 67P/Churyumov–Gerasimenko traversing <a href="http://www.esa.int/Our_Activities/Space_Science/Rosetta/Rosetta_s_big_day_in_the_Sun">its perihelion</a>.<br /><div style="text-align: center;">
<br /></div>
<div style="text-align: center;">
<a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEheOQ4DvehJk8zDOv15KR9C0KMJvVNTjQGZOpV3tDBo9BQ3Mc0pFZ856Iv_M5MEqNE8XlR6hvv7H1IDiMFhpIyPBcJGWlqTGJnmicI_rr3M9QfIfVJuQGN7wdh_zh1rN6wo8oZymPnOmtU/s1600/Approaching_perihelion_Animation_node_full_image_2.gif" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" height="400" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEheOQ4DvehJk8zDOv15KR9C0KMJvVNTjQGZOpV3tDBo9BQ3Mc0pFZ856Iv_M5MEqNE8XlR6hvv7H1IDiMFhpIyPBcJGWlqTGJnmicI_rr3M9QfIfVJuQGN7wdh_zh1rN6wo8oZymPnOmtU/s400/Approaching_perihelion_Animation_node_full_image_2.gif" width="400" /></a></div>
<div style="text-align: center;">
<br /></div>
</li>
<li>Those in the Northern Hemisphere were lucky to have an almost-new moon for the Perseids this year. (The shot below is from <a href="https://www.facebook.com/rmsphotography95">Ruslan Merzlyakov</a>).<br /><br /><div style="text-align: center;">
<a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEi0vq8RRNZjlrEZ_uQF0Y1fQwjJocaD8Go1VGwF5ZDGoJfmMc_vAifmqFren08kN2uAjh8nefprehjWcDVpPy_ry9ujxBVFehiWl_rD5oAvCtd_AbLAkP1K9zhcwsKumPTDNNCyaSOiFxs/s1600/perseids-2015-denmark-merzlyakov.jpg" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" height="377" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEi0vq8RRNZjlrEZ_uQF0Y1fQwjJocaD8Go1VGwF5ZDGoJfmMc_vAifmqFren08kN2uAjh8nefprehjWcDVpPy_ry9ujxBVFehiWl_rD5oAvCtd_AbLAkP1K9zhcwsKumPTDNNCyaSOiFxs/s400/perseids-2015-denmark-merzlyakov.jpg" width="400" /></a></div>
<br />Check out the slideshow <a href="http://www.space.com/30218-perseid-meteor-shower-photos-2015.html">at space.com</a>.</li>
</ul>
Bluejayhttp://www.blogger.com/profile/06935684943024856641noreply@blogger.com0tag:blogger.com,1999:blog-959149188511266512.post-13560023821399885182015-08-07T17:03:00.002+10:002015-09-11T10:27:19.551+10:00Friday wrap-up: normal ordering, hierarchy problem...Wherein I list some (mostly) recent happenings, ramble a bit, and provide links, in an order roughly determined by importance and relevance to particle physics. Views are my own. Content very definitely skewed by my own leanings and by papers getting coverage, and it may not even be correct. It is a blog after all...<br />
<br />
<ul>
<li>First point for today is hot off the press! The long baseline NOvA experiment <a href="http://nova-docdb.fnal.gov/cgi-bin/ShowDocument?docid=13883">has released</a> a preliminary analysis of $\nu_e$ appearance in their beam. They exclude inverted ordering at >2σ, preferring normal ordering with $\delta_{CP}\approx 3\pi/2$! Slides <a href="http://theory.fnal.gov/jetp/talks/20150806_nova_docdb.pdf">here [pdf]</a>.<br /><br /><div class="separator" style="clear: both; text-align: center;">
<a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgEwlggdyuCQGT_UyCcX68GtTW1YWCk9_KjkD1pwFDj8vj6nzUpDRdiMMPKmufq8oqE4YlRNsXTfW9UrqpoR1ReaEH7FjtqkYT3RRjhwsNZ-x1295o5rQeTLug4KVAwb3YHBYtydk8Ll0Y/s1600/Screenshot+from+2015-08-07+15%253A30%253A02.png" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" height="300" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgEwlggdyuCQGT_UyCcX68GtTW1YWCk9_KjkD1pwFDj8vj6nzUpDRdiMMPKmufq8oqE4YlRNsXTfW9UrqpoR1ReaEH7FjtqkYT3RRjhwsNZ-x1295o5rQeTLug4KVAwb3YHBYtydk8Ll0Y/s400/Screenshot+from+2015-08-07+15%253A30%253A02.png" width="400" /></a></div>
<div style="text-align: center;">
<br /></div>
</li>
<li>Quite a few conferences recently: Second Conference on Heavy Ion Collisions in the LHC era and beyond (<a href="https://indico.cern.ch/event/327279/">indico</a>/<a href="https://twitter.com/hashtag/renviet15?f=tweets&vertical=default&src=hash">hashtag</a>), 34th International Cosmic Ray Conference (<a href="https://indico.cern.ch/event/344485/">indico</a>/<a href="https://twitter.com/hashtag/icrc2015?f=tweets&vertical=default&src=hash">hashtag</a>), and the 2015 Meeting of the APS Division of Particles and Fields (<a href="https://indico.cern.ch/event/361123/">indico</a>/<a href="https://twitter.com/hashtag/dpf2015?f=tweets&vertical=default&src=hash">hashtag</a>) which is still going.</li>
</ul>
<ul>
<li><a href="http://cms.web.cern.ch/org/physics-papers-timeline">CMS publications</a> as a function of time and physics group.</li>
</ul>
<ul>
<li>Quanta Magazine have mapped out <a href="https://www.quantamagazine.org/20150803-physics-theories-map/">a nice interactive</a> "Theories of Everything" applet.</li>
</ul>
<ul>
<li>An <a href="http://www.pbs.org/wgbh/nova/blogs/physics/?p=2240">excerpt from</a> and a <a href="http://www.theguardian.com/books/2015/aug/01/a-beautiful-question-natures-deep-design-frank-wilczek-review">review of</a> Wilczek's new book.</li>
</ul>
<ul>
<li>In video/audio media:</li>
<ul>
<li>Neil deGrasse Tyson <a href="http://iview.abc.net.au/programs/qanda/FA1407H027S00?">on Q&A</a>. [1 hour]</li>
<li><a href="https://youtu.be/Ig35vEImzYE">LHC Computing</a> with Don Lincoln from Fermilab. [6 minutes]</li>
<li><a href="https://youtu.be/zY-PBkxAE0Y">Coffee physics</a> on Sixty Symbols. [8 minutes]</li>
<li><a href="https://youtu.be/aqyyhhnGraw">Knots</a> on numberphile. [11 minutes]</li>
</ul>
</ul>
<ul>
<li>Here is a <a href="https://www.nasa.gov/feature/goddard/from-a-million-miles-away-nasa-camera-shows-moon-crossing-face-of-earth">view from NASA's DSCOVR</a> satellite (floating at the Lagrange point between the Sun and Earth) of the sunlit "dark side" of the moon.<br /><br /><div style="text-align: center;">
<a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhWl7f4ug1sxcyzz9R-CUMdEOFjwFa4nLYvPcryFBE04iNOtwCDx0_c5KxmqNHc10N7JNEElY9U4kaqNRpBjzKoTNSTHPY7Vp5R48AZtDDW_Pjk567pCxVrtGtTbV3vXgRz_ZTq3v9ZaKg/s1600/dscovrepicmoontransitfull.gif" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" height="223" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhWl7f4ug1sxcyzz9R-CUMdEOFjwFa4nLYvPcryFBE04iNOtwCDx0_c5KxmqNHc10N7JNEElY9U4kaqNRpBjzKoTNSTHPY7Vp5R48AZtDDW_Pjk567pCxVrtGtTbV3vXgRz_ZTq3v9ZaKg/s400/dscovrepicmoontransitfull.gif" width="400" /></a></div>
</li>
</ul>
<br />
Now something a little different... <br />
<br />
<i>[Note: some edits on 11th September to distinguish between a hierarchy problem and a naturalness problem].</i><br />
<br />
I have been thinking a lot about the hierarchy problem and Higgs mass naturalness over this year. I have come to the (controversial?) conclusion that <b>the standard model with gravity does not <i>obviously</i> suffer from a naturalness problem</b>. For my own benefit this week I wanted to jot down my thoughts, and also decided to share, as it seems to me to somehow be a widely misunderstood subject... [caveats from first paragraph still hold! and discussion/comments are welcome]...<br />
<br />
The standard model Higgs potential is$$V_{SM} = \mu^2 \phi^\dagger \phi + \lambda (\phi^\dagger\phi)^2 .$$Since 2012, we have known that $\mu^2 \approx - (88\text{ GeV})^2$ (at low energies). I take the hierarchy problem to be: <b>why is $\mu^2$ so small compared to $M_{Pl}\sim 10^{19}\text{ GeV}$?</b> I take a naturalness problem as: <b>$\mu^2$ is sensitive to very large ($\gtrsim (1\text{ TeV})^2$) and physically meaningful quantum corrections</b>.<b> </b>But let's first consider <b>the standard model without gravity</b>...<br />
<br />
Like all bare parameters in a quantum field theory, the unmeasurable bare parameter $\mu^2$ must be connected to a measurable friend, say $\mu^2(m_Z)$. We do this by renormalising the theory, i.e. we calculate quantum corrections, cancel them off with the bare parameter, and connect what we have left to some observable. In a cutoff regularisation scheme, the dominant one-loop quantum correction to $\mu^2$ comes from the top quark and goes something like$$\delta\mu^2 \sim \frac{1}{(4\pi)^2} y_t^2 \left( \Lambda^2 + ...\right),$$where $\Lambda$ is a cutoff renormalisation scale. Renormalisation demands that this potentially large quantum contribution be cancelled off with the bare parameter in order to arrive at an electroweak scale $\mu^2(m_Z)$. One might worry about these "unnaturally" large cancellations. However, in the standard model without gravity this scale is completely arbitrary... it is unphysical! We should assign no physical significance to a large cancellation between an unmeasurable bare parameter and an unphysical cutoff -- this much we should have learned when we studied renormalisation. We don't have to worry about quadratic corrections to $\mu^2$ that are $\propto \Lambda^2$, in short since the standard model without gravity has only one explicit scale, so how can $\mu^2$ be corrected by anything other than $\mu^2$ itself? [Note: scale invariance is broken by quantum corrections and so this argument doesn't extend to dynamical scales: a little more later].<br />
<br />
So what is physical? What exactly is the effect of the top quark on $\mu^2$? For me this becomes more clear in a dimensional regularisation scheme. The one-loop quantum correction to $\mu^2$ will go something like$$\delta\mu^2 \sim \frac{1}{(4\pi)^2}y_t^2\mu^2\left(\frac{1}{\epsilon}+ \text{ finite terms} +\ln\mu_R \right)$$where $\mu_R$ is a renormalisation scale and we take the limit $\epsilon\to 0$. The divergent term $\propto 1/\epsilon$ and the finite terms can be cancelled against a counterterm in the bare parameter. This is another way of saying <b>they are unphysical</b>. However, <b>the term $\propto \ln\mu_R$ cannot be always absorbed</b> and has an observable effect. Any observable must not depend on $\mu_R$, and (in a mass-independent renormalisation scheme) the counterterm must also be independent of $\mu_R$. After a little algebra this ends up implying that the $\mu^2$ parameter depends on the scale at which it is measured, $\mu^2=\mu^2(\mu_R)$, a familiar result of renormalisation in quantum field theories (see e.g. the 2004 Nobel Prize in Physics). In the standard model the top quark contribution turns out to be$$\frac{d\mu^2}{d\ln\mu_R}\approx\frac{1}{(4\pi)^2}6y_t^2\mu^2.$$This is called the renormalisation group equation (RGE) for $\mu^2$. You can see it's $\propto \mu^2$, which is just <i>another</i> way of saying that the standard model without gravity has only one explicit scale. The only physical (and in-principle measurable) effect of the top quark on the $\mu^2$ parameter is to make it run with energy. And it doesn't run much! You can easily calculate that $\mu^2$ remains $\mathcal{O}(\mu^2)$ even up to a scale $\mu_R\sim 10^{19}\text{ GeV}$. That means that a small change in $\mu^2$ at some high scale results also in a corresponding small change in $\mu^2$ at a low scale, which is exactly the Barbieri-Giudice style fine-tuning requirement for a natural theory.<br />
<br />
I like this RGE formulation of the hierarchy problem because it is physical: it is phrased in terms of an in-principle measurable parameter $\mu^2(\mu_R)$ and a quantifiable fine-tuning of that parameter at a high scale. If any perturbative new physics is added to the standard model one can just calculate its effect on the $\mu^2$ RGE and see if it results in fine-tuning at a high scale. In this sort of approach the requirement for a natural electroweak scale is just that $\frac{d\mu^2}{d\ln\mu_R} \lesssim (100\text{ GeV})^2$.<br />
<br />
So in particular, and this is a fallacy I hear a lot, in the standard model without gravity <b>there are no top quark loop divergences that must be cancelled with new particles</b> -- that has already been achieved for you with renormalisation.<br />
<br />
I am not positive why this top loop quadratic divergence argument has gained traction, but I think the following is a reasonable possibility. In a generic new physics model, one fear is that the top quark, being strongly coupled to the Higgs, might also strongly couple to some other (higher) scale, and "transmit" that scale to $\mu^2$, i.e. one fears a quantum correction to $\mu^2$ that is $\propto y_t^2M_{NP}^2$. One would not have to worry if there was a new particle(s) which by some symmetry transmits an equal and opposite contribution to $\delta\mu^2$, such that they cancel. This is achieved in supersymmetry (SUSY) by the stop $\tilde{t}$. In dimensional regularisation the stop will give a $\delta\mu^2$ contribution which differs from the top contribution only by a negative sign and a factor $m_\tilde{t}^2/m_t^2$; they exactly cancel if $m_{\tilde{t}}=m_t$. But the fact that the divergent terms (to be associated with the quadratic divergences) cancel is beside the point, since they are unphysical anyway. What matters is the contribution to the $\mu^2$ RGE, and at one-loop the top/stop contributions together will result in a term proportional to the mass splitting,$$\frac{d\mu^2}{d\ln\mu_R}\approx \frac{1}{(4\pi)^2}6y_t^2\frac{\mu^2}{m_t^2}\left(m_t^2-m_\tilde{t}^2\right).$$The fine-tuning argument now demands the RHS be $\lesssim (100\text{ GeV})^2$. Unless the stop is sufficiently light, $\mu^2(\mu_R)$ will run to very large values at large scales, creating a fine-tuning problem, or an unnatural theory. Now, note that if you identify the splitting with the cutoff scale $\Lambda^2$ (makes sense if $m_t\ll m_{\tilde{t}}\sim M_{SUSY}$) then the fine-tuning condition gives roughly$$\frac{1}{(4\pi)^2} y_t^2\Lambda^2 \lesssim (100\text{ GeV})^2,$$which looks just like a quadratic cutoff correction due to the top. That equation taken out of context suggests that the appearance of the stop is acting to cancel any larger quadratic loop divergences of the top. Such an interpretation gives the right naturalness bound but for the wrong reasons... the correction has nothing necessarily to do with a cutoff and everything to do with a strongly coupled heavy particle: the stop. <b>Without the stop there is no problem!</b> Renormalisation takes care of the divergent term.<br />
<br />
There is one extra point to be covered to wrap up this conversation about the standard model without gravity. The standard model is not asymptotically free and therefore a very high dynamical scale is generated. In particular, the one-loop RGE for the $U(1)_Y$ gauge coupling is positive, and at $\mu_R\sim 10^{40}\text{ GeV}$ it hits a Landau Pole, i.e. the coupling appears to $\to\infty$. So you might ask: does this introduce a dynamical scale which will correct $\mu^2$? Does it make an electroweak $\mu^2$ unnatural? The answer to this question is not obvious to me. Such a theory is clearly transitioning into a non-perturbative regime. I can't carry out a calculation here (nobody can). Certainly a hand-waving one-loop argument for contributions to $\mu^2$ no longer holds. Furthermore it is not even clear to me that the Higgs field is a sensible degree of freedom in such a regime. Anyway, the worry is moot, since the assumption of a flat spacetime at this scale is not even close to valid; one expects quantum gravitational states to come in at latest the Planck scale $M_{Pl}\sim 10^{19}\text{ GeV}$, so about that...<br />
<br />
So far we have argued that the standard model without gravity in flat spacetime suffers no obvious naturalness problem. Okay, but we <i>have</i> measured another fundamental mass scale in physics: $M_{Pl}\sim 10^{19}\text{ GeV}$. [Let it be clear that $M_{Pl}$ is only a dimensional argument; it is defined as $1/M_{Pl}^2 := G_{N}$, where $G_{N}$ is Newton's constant which enters Einstein's equations for general relativity]. Should we be worried?<br />
<br />
For <b>the standard model with gravity</b>, the argument I often see goes something like the following: because of gravity, the standard model is at best an effective theory up to $M_{Pl}$, at which point we know new physics must come in, making the cutoff at $\Lambda^2\sim M_{Pl}^2$ physical and thereby making large cancellations unnatural. The argument has at least three holes. <b>(1) </b>The appearance of an apparently large scale $M_{Pl}$ in an effective theory does not necessarily imply quantum states at a scale $M_{Pl}$ (see e.g. large extra dimensions). <b>(2) </b>Even if it did, we don't have a quantum theory of gravity, and so we can't calculate the corrections to $\mu^2$ to convince ourselves there is a definite problem. Even naively, the one-loop flat spacetime correction is sure to be altered in some way. <b>(3)</b> Perhaps the most important point: <b>the existence of some large mass quantum states</b> coupled to the standard model (and therefore a large and physical cutoff to the standard model) <b>does not necessarily imply a naturalness problem.</b><br />
<br />
Let me illustrate in particular points (1) and (3) above with an example: neutrino masses. Suppose you are convinced that neutrino masses are Majorana and generated by an effective dimension 5 Weinberg operator $ l\phi l\phi/\Lambda$ after electroweak symmetry breaking, so that$$m_\nu = v^2/\Lambda,$$where $v\approx 174\text{ GeV}$ is the Higgs vev. You then measure $m_\nu\sim 0.05\text{ eV}$ in experiment, suggesting $\Lambda \sim 10^{15}\text{ GeV}$. So the dimensional argument has lead to an apparent hierarchy and you fear a naturalness problem. The argument then goes: if the effective Weinberg description of neutrino masses is true then it looks like the standard model is at best a good effective theory up to $10^{15}\text{ GeV}$, and you know the rest...<br />
<br />
But now let's look at a UV-complete model: the Type I see-saw. Add a heavy right-handed neutrino $N$ of mass $M_N$, with a Yukawa term $y\ l \phi N$, and integrate it out to match onto the Weinberg operator; you find $$1/\Lambda \equiv y^2/M_N.$$The correction to $\mu^2$ can be easily calculated as$$\frac{d\mu^2}{d\ln\mu_R} \sim -\frac{1}{(4\pi)^2}y^2 M_N^2 \sim -\frac{1}{(4\pi)^2} m_\nu M_N^3 / v^2.$$Plug in the numbers yourself and see that for $M_N\lesssim 10^7\text{ GeV}$ there is no large correction to $\mu^2$ (there's not even a large finite correction). How can this be? The reason is that <b>as $M_N$ becomes smaller so does $y^2$,</b> in order to reproduce the observed neutrino mass; both work together to lower the correction to $\mu^2$. For $M_N\sim 10^7\text{ GeV}$ you'll find $y \sim 10^{-4}$. One might get uncomfortable about a small coupling in the theory. However the limit $y\to 0$ increases the symmetry of the theory by decoupling $N$ (it also reinstates a $U(1)_L$ symmetry), and so corrections to $y$ can only be proportional to $y$ itself. [This is is called a technically natural limit, and it is the very reason that we do not worry about a naturalness problem for the standard model fermion masses].<br />
<br />
Anyway, I have just given an example where a dimensional argument makes you think that there is a very large scale $\sim 10^{15}\text{ GeV}$ in the theory, when a small coupling is just tricking you, and even the existence of a large scale $\sim 10^7\text{ GeV}$ in the renormalisable theory <i>calculably</i> does not introduce a naturalness problem, thanks again to a small coupling (which is technically natural). These observations alone, even without point (2) I made above, are enough to convince me that the standard model with gravity does not necessarily have a naturalness problem.<br />
<br />
So why do we often hear that it does? I am not positive, but I suspect that there are historical reasons for this. Grand unified models look so (subjectively) aesthetically pleasing that it is easy to want to believe in them. If you are set on a grand unified theory at $10^{15}\text{ GeV}$, then there are going to be strongly coupled heavy vector fields which correct $\mu^2$ in a calculable way,$$\frac{d\mu^2}{d\ln\mu_R} \sim \frac{1}{(4\pi)^2}g^2 M_{GUT}^2,$$<br />
or at two-loop. This necessarily leads to a naturalness problem (the "gauge hierarchy problem") unless you come up with some mechanism to cancel away these contributions. SUSY is a very nice mechanism for doing this (perhaps the nicest, but that is subjective) and as a bonus you also protect yourself from $M_{Pl}$ and anything else up there! But if you introduce it you have to have it come in at around the TeV scale, otherwise the new strongly coupled heavy particles (e.g. the stops) will create their own naturalness problem anyway...<br />
<br />
And so we wait for LHC Run II to reconnect us with experiment and perhaps shed some light...Bluejayhttp://www.blogger.com/profile/06935684943024856641noreply@blogger.com2tag:blogger.com,1999:blog-959149188511266512.post-74497740485482343042015-08-03T14:52:00.000+10:002015-08-03T14:52:39.908+10:00arXiv-watch: May-Jul 2015The top five cited articles in hep/astro (according to INSPIRE) of the last three months overall.<br />
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All <a href="http://syymmetries.blogspot.com.au/2015/07/friday-wrap-up-diboson-excess-eps-hep.html">diboson</a> papers...<br />
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<table style="color: black; font-family: arial, verdana, sans-serif;"><tbody>
<tr><td align="right" style="white-space: nowrap;" valign="top">1.<br />
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<a href="https://www.blogger.com/null" title="rank score">(40)</a></div>
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<a class="titlelink" href="http://inspirehep.net/record/1374218" style="background-attachment: initial; background-clip: initial; background-image: initial; background-origin: initial; background-position: initial; background-repeat: initial; background-size: initial; color: black; font-weight: bold; text-decoration: none;">Search for high-mass diboson resonances with boson-tagged jets in proton-proton collisions at <span style="white-space: nowrap;">$\sqrt{s}=8$</span> TeV with the ATLAS detector</a><br />
<small><a class="authorlink" href="http://inspirehep.net/search?p=collaboration:%27ATLAS%27&ln=en" style="color: #6699cc; text-decoration: none;">ATLAS</a> Collaboration (<a class="authorlink" href="http://inspirehep.net/author/profile/Aad%2C%20Georges?recid=1374218&ln=en" style="color: #6699cc; text-decoration: none;">Georges Aad</a> (<a class="afflink" href="http://inspirehep.net/search?cc=Institutions&p=institution:%22Marseille%2C%20CPPM%22&ln=en" style="color: #6699cc; text-decoration: none;">Marseille, CPPM</a>)<a class="authorlink" href="http://inspirehep.net/record/1374218" style="color: #6699cc; text-decoration: none;"><i> et al.</i></a>). Jun 2, 2015. 37 pp.<br />CERN-PH-EP-2015-115<br />e-Print: <b><a href="http://arxiv.org/abs/arXiv:1506.00962" style="color: #6699cc;">arXiv:1506.00962</a> [hep-ex] | <a href="http://arxiv.org/pdf/1506.00962.pdf" style="color: #6699cc;">PDF</a></b></small><br />
<ul class="tight_list" style="font-size: small; list-style: none; margin: 0.5ex 0px 0px;">
<li><a href="http://inspirehep.net/record/1374218/references" style="color: #6699cc;">References</a> | <a href="http://inspirehep.net/record/1374218/export/hx" style="color: #6699cc;">BibTeX</a> | <a href="http://inspirehep.net/record/1374218/export/hlxu" style="color: #6699cc;">LaTeX(US)</a> | <a href="http://inspirehep.net/record/1374218/export/hlxe" style="color: #6699cc;">LaTeX(EU)</a> | <a href="http://inspirehep.net/record/1374218/export/hlxh" style="color: #6699cc;">Harvmac</a> | <a href="http://inspirehep.net/record/1374218/export/xe" style="color: #6699cc;">EndNote</a></li>
<li><a href="http://cds.cern.ch/record/2021093" style="color: #6699cc;">CERN Document Server </a>; <a href="http://adsabs.harvard.edu/cgi-bin/basic_connect?qsearch=arXiv:1506.00962" style="color: #6699cc;">ADS Abstract Service</a></li>
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</ul>
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<span class="moreinfo" style="background-attachment: initial; background-clip: initial; background-image: initial; background-origin: initial; background-position: initial; background-repeat: initial; background-size: initial;"><a class="moreinfo" href="http://inspirehep.net/record/1374218?ln=en" style="background-attachment: initial; background-clip: initial; background-image: initial; background-origin: initial; background-position: initial; background-repeat: initial; background-size: initial; color: #006600;">Detailed record</a></span><span class="moreinfo" style="background-attachment: initial; background-clip: initial; background-image: initial; background-origin: initial; background-position: initial; background-repeat: initial; background-size: initial;"> - <a class="moreinfo" href="http://inspirehep.net/search?ln=en&p=refersto%3Arecid%3A1374218&sf=earliestdate&rm=citation" style="background-attachment: initial; background-clip: initial; background-image: initial; background-origin: initial; background-position: initial; background-repeat: initial; background-size: initial; color: #006600;">Cited by 40 records</a></span></div>
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<tr><td align="right" style="white-space: nowrap;" valign="top"><abbr class="unapi-id" title="1375823"></abbr>2.<br />
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<a href="https://www.blogger.com/null" title="rank score">(27)</a></div>
</td><td valign="top"><div class="record_body">
<a class="titlelink" href="http://inspirehep.net/record/1375823" style="background-attachment: initial; background-clip: initial; background-image: initial; background-origin: initial; background-position: initial; background-repeat: initial; background-size: initial; color: black; font-weight: bold; text-decoration: none;">2 TeV Walking Technirho at LHC?</a><br />
<small><a class="authorlink" href="http://inspirehep.net/author/profile/Fukano%2C%20Hidenori%20S.?recid=1375823&ln=en" style="color: #6699cc; text-decoration: none;">Hidenori S. Fukano</a> (<a class="afflink" href="http://inspirehep.net/search?cc=Institutions&p=institution:%22KMI%2C%20Nagoya%22&ln=en" style="color: #6699cc; text-decoration: none;">KMI, Nagoya</a>), <a class="authorlink" href="http://inspirehep.net/author/profile/Kurachi%2C%20Masafumi?recid=1375823&ln=en" style="color: #6699cc; text-decoration: none;">Masafumi Kurachi</a> (<a class="afflink" href="http://inspirehep.net/search?cc=Institutions&p=institution:%22KEK%2C%20Tsukuba%22&ln=en" style="color: #6699cc; text-decoration: none;">KEK, Tsukuba</a>), <a class="authorlink" href="http://inspirehep.net/author/profile/Matsuzaki%2C%20Shinya?recid=1375823&ln=en" style="color: #6699cc; text-decoration: none;">Shinya Matsuzaki</a> (<a class="afflink" href="http://inspirehep.net/search?cc=Institutions&p=institution:%22Nagoya%20U.%22&ln=en" style="color: #6699cc; text-decoration: none;">Nagoya U.</a>), <a class="authorlink" href="http://inspirehep.net/author/profile/Terashi%2C%20Koji?recid=1375823&ln=en" style="color: #6699cc; text-decoration: none;">Koji Terashi</a> (<a class="afflink" href="http://inspirehep.net/search?cc=Institutions&p=institution:%22Tokyo%20U.%22&ln=en" style="color: #6699cc; text-decoration: none;">Tokyo U.</a> & <a class="afflink" href="http://inspirehep.net/search?cc=Institutions&p=institution:%22Tokyo%20U.%2C%20ICEPP%22&ln=en" style="color: #6699cc; text-decoration: none;">Tokyo U., ICEPP</a>), <a class="authorlink" href="http://inspirehep.net/author/profile/Yamawaki%2C%20Koichi?recid=1375823&ln=en" style="color: #6699cc; text-decoration: none;">Koichi Yamawaki</a> (<a class="afflink" href="http://inspirehep.net/search?cc=Institutions&p=institution:%22KMI%2C%20Nagoya%22&ln=en" style="color: #6699cc; text-decoration: none;">KMI, Nagoya</a>). Jun 11, 2015. 9 pp.<br />KEK-TH-1834<br />e-Print: <b><a href="http://arxiv.org/abs/arXiv:1506.03751" style="color: #6699cc;">arXiv:1506.03751</a> [hep-ph] | <a href="http://arxiv.org/pdf/1506.03751.pdf" style="color: #6699cc;">PDF</a></b></small><br />
<ul class="tight_list" style="font-size: small; list-style: none; margin: 0.5ex 0px 0px;">
<li><a href="http://inspirehep.net/record/1375823/references" style="color: #6699cc;">References</a> | <a href="http://inspirehep.net/record/1375823/export/hx" style="color: #6699cc;">BibTeX</a> | <a href="http://inspirehep.net/record/1375823/export/hlxu" style="color: #6699cc;">LaTeX(US)</a> | <a href="http://inspirehep.net/record/1375823/export/hlxe" style="color: #6699cc;">LaTeX(EU)</a> | <a href="http://inspirehep.net/record/1375823/export/hlxh" style="color: #6699cc;">Harvmac</a> | <a href="http://inspirehep.net/record/1375823/export/xe" style="color: #6699cc;">EndNote</a></li>
<li><a href="http://adsabs.harvard.edu/cgi-bin/basic_connect?qsearch=arXiv:1506.03751" style="color: #6699cc;">ADS Abstract Service</a></li>
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<span class="moreinfo" style="background-attachment: initial; background-clip: initial; background-image: initial; background-origin: initial; background-position: initial; background-repeat: initial; background-size: initial;"><a class="moreinfo" href="http://inspirehep.net/record/1375823?ln=en" style="background-attachment: initial; background-clip: initial; background-image: initial; background-origin: initial; background-position: initial; background-repeat: initial; background-size: initial; color: #006600;">Detailed record</a></span><span class="moreinfo" style="background-attachment: initial; background-clip: initial; background-image: initial; background-origin: initial; background-position: initial; background-repeat: initial; background-size: initial;"> - <a class="moreinfo" href="http://inspirehep.net/search?ln=en&p=refersto%3Arecid%3A1375823&sf=earliestdate&rm=citation" style="background-attachment: initial; background-clip: initial; background-image: initial; background-origin: initial; background-position: initial; background-repeat: initial; background-size: initial; color: #006600;">Cited by 27 records</a></span></div>
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<tr><td align="right" style="white-space: nowrap;" valign="top"><abbr class="unapi-id" title="1377366"></abbr>3.<br />
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<a href="https://www.blogger.com/null" title="rank score">(26)</a></div>
</td><td valign="top"><div class="record_body">
<a class="titlelink" href="http://inspirehep.net/record/1377366" style="background-attachment: initial; background-clip: initial; background-image: initial; background-origin: initial; background-position: initial; background-repeat: initial; background-size: initial; color: black; font-weight: bold; text-decoration: none;">A W' boson near 2 TeV: predictions for Run 2 of the LHC</a><br />
<small><a class="authorlink" href="http://inspirehep.net/author/profile/Dobrescu%2C%20Bogdan%20A.?recid=1377366&ln=en" style="color: #6699cc; text-decoration: none;">Bogdan A. Dobrescu</a> (<a class="afflink" href="http://inspirehep.net/search?cc=Institutions&p=institution:%22Fermilab%22&ln=en" style="color: #6699cc; text-decoration: none;">Fermilab</a>), <a class="authorlink" href="http://inspirehep.net/author/profile/Liu%2C%20Zhen?recid=1377366&ln=en" style="color: #6699cc; text-decoration: none;">Zhen Liu</a> (<a class="afflink" href="http://inspirehep.net/search?cc=Institutions&p=institution:%22Fermilab%22&ln=en" style="color: #6699cc; text-decoration: none;">Fermilab</a> & <a class="afflink" href="http://inspirehep.net/search?cc=Institutions&p=institution:%22Pittsburgh%20U.%22&ln=en" style="color: #6699cc; text-decoration: none;">Pittsburgh U.</a>). Jun 22, 2015. 5 pp.<br />FERMILAB-PUB-15-265-T-, PITT-PACC-1508, FERMILAB-PUB-15-265-T<br />e-Print: <b><a href="http://arxiv.org/abs/arXiv:1506.06736" style="color: #6699cc;">arXiv:1506.06736</a> [hep-ph] | <a href="http://arxiv.org/pdf/1506.06736.pdf" style="color: #6699cc;">PDF</a></b></small><br />
<ul class="tight_list" style="font-size: small; list-style: none; margin: 0.5ex 0px 0px;">
<li><a href="http://inspirehep.net/record/1377366/references" style="color: #6699cc;">References</a> | <a href="http://inspirehep.net/record/1377366/export/hx" style="color: #6699cc;">BibTeX</a> | <a href="http://inspirehep.net/record/1377366/export/hlxu" style="color: #6699cc;">LaTeX(US)</a> | <a href="http://inspirehep.net/record/1377366/export/hlxe" style="color: #6699cc;">LaTeX(EU)</a> | <a href="http://inspirehep.net/record/1377366/export/hlxh" style="color: #6699cc;">Harvmac</a> | <a href="http://inspirehep.net/record/1377366/export/xe" style="color: #6699cc;">EndNote</a></li>
<li><a href="http://adsabs.harvard.edu/cgi-bin/basic_connect?qsearch=arXiv:1506.06736" style="color: #6699cc;">ADS Abstract Service</a></li>
<li></li>
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<span class="moreinfo" style="background-attachment: initial; background-clip: initial; background-image: initial; background-origin: initial; background-position: initial; background-repeat: initial; background-size: initial;"><a class="moreinfo" href="http://inspirehep.net/record/1377366?ln=en" style="background-attachment: initial; background-clip: initial; background-image: initial; background-origin: initial; background-position: initial; background-repeat: initial; background-size: initial; color: #006600;">Detailed record</a></span><span class="moreinfo" style="background-attachment: initial; background-clip: initial; background-image: initial; background-origin: initial; background-position: initial; background-repeat: initial; background-size: initial;"> - <a class="moreinfo" href="http://inspirehep.net/search?ln=en&p=refersto%3Arecid%3A1377366&sf=earliestdate&rm=citation" style="background-attachment: initial; background-clip: initial; background-image: initial; background-origin: initial; background-position: initial; background-repeat: initial; background-size: initial; color: #006600;">Cited by 26 records</a></span></div>
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<tr><td align="right" style="white-space: nowrap;" valign="top"><abbr class="unapi-id" title="1376127"></abbr>4.<br />
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<a href="https://www.blogger.com/null" title="rank score">(26)</a></div>
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<a class="titlelink" href="http://inspirehep.net/record/1376127" style="background-attachment: initial; background-clip: initial; background-image: initial; background-origin: initial; background-position: initial; background-repeat: initial; background-size: initial; color: black; font-weight: bold; text-decoration: none;">Diboson Signals via Fermi Scale Spin-One States</a><br />
<small><a class="authorlink" href="http://inspirehep.net/author/profile/Franzosi%2C%20Diogo%20Buarque?recid=1376127&ln=en" style="color: #6699cc; text-decoration: none;">Diogo Buarque Franzosi</a>, <a class="authorlink" href="http://inspirehep.net/author/profile/Frandsen%2C%20Mads%20T.?recid=1376127&ln=en" style="color: #6699cc; text-decoration: none;">Mads T. Frandsen</a>, <a class="authorlink" href="http://inspirehep.net/author/profile/Sannino%2C%20Francesco?recid=1376127&ln=en" style="color: #6699cc; text-decoration: none;">Francesco Sannino</a> (<a class="afflink" href="http://inspirehep.net/search?cc=Institutions&p=institution:%22Southern%20Denmark%20U.%2C%20CP3-Origins%22&ln=en" style="color: #6699cc; text-decoration: none;">Southern Denmark U., CP3-Origins</a> & <a class="afflink" href="http://inspirehep.net/search?cc=Institutions&p=institution:%22U.%20Southern%20Denmark%2C%20Odense%2C%20DIAS%22&ln=en" style="color: #6699cc; text-decoration: none;">U. Southern Denmark, Odense, DIAS</a>). Jun 14, 2015. 4 pp.<br />CP3-ORIGINS-2015-023-DNRF90, DIAS-2015-23<br />e-Print: <b><a href="http://arxiv.org/abs/arXiv:1506.04392" style="color: #6699cc;">arXiv:1506.04392</a> [hep-ph] | <a href="http://arxiv.org/pdf/1506.04392.pdf" style="color: #6699cc;">PDF</a></b></small><br />
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<li><a href="http://inspirehep.net/record/1376127/references" style="color: #6699cc;">References</a> | <a href="http://inspirehep.net/record/1376127/export/hx" style="color: #6699cc;">BibTeX</a> | <a href="http://inspirehep.net/record/1376127/export/hlxu" style="color: #6699cc;">LaTeX(US)</a> | <a href="http://inspirehep.net/record/1376127/export/hlxe" style="color: #6699cc;">LaTeX(EU)</a> | <a href="http://inspirehep.net/record/1376127/export/hlxh" style="color: #6699cc;">Harvmac</a> | <a href="http://inspirehep.net/record/1376127/export/xe" style="color: #6699cc;">EndNote</a></li>
<li><a href="http://adsabs.harvard.edu/cgi-bin/basic_connect?qsearch=arXiv:1506.04392" style="color: #6699cc;">ADS Abstract Service</a></li>
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<tr><td align="right" style="white-space: nowrap;" valign="top"><abbr class="unapi-id" title="1376004"></abbr>5.<br />
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<a href="https://www.blogger.com/null" title="rank score">(26)</a></div>
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<a class="titlelink" href="http://inspirehep.net/record/1376004" style="background-attachment: initial; background-clip: initial; background-image: initial; background-origin: initial; background-position: initial; background-repeat: initial; background-size: initial; color: black; font-weight: bold; text-decoration: none;">Interpretations of the ATLAS Diboson Resonances</a><br />
<small><a class="authorlink" href="http://inspirehep.net/author/profile/Hisano%2C%20Junji?recid=1376004&ln=en" style="color: #6699cc; text-decoration: none;">Junji Hisano</a> (<a class="afflink" href="http://inspirehep.net/search?cc=Institutions&p=institution:%22KMI%2C%20Nagoya%22&ln=en" style="color: #6699cc; text-decoration: none;">KMI, Nagoya</a> & <a class="afflink" href="http://inspirehep.net/search?cc=Institutions&p=institution:%22Nagoya%20U.%22&ln=en" style="color: #6699cc; text-decoration: none;">Nagoya U.</a> & <a class="afflink" href="http://inspirehep.net/search?cc=Institutions&p=institution:%22Tokyo%20U.%2C%20IPMU%22&ln=en" style="color: #6699cc; text-decoration: none;">Tokyo U., IPMU</a>), <a class="authorlink" href="http://inspirehep.net/author/profile/Nagata%2C%20Natsumi?recid=1376004&ln=en" style="color: #6699cc; text-decoration: none;">Natsumi Nagata</a> (<a class="afflink" href="http://inspirehep.net/search?cc=Institutions&p=institution:%22Tokyo%20U.%2C%20IPMU%22&ln=en" style="color: #6699cc; text-decoration: none;">Tokyo U., IPMU</a> & <a class="afflink" href="http://inspirehep.net/search?cc=Institutions&p=institution:%22Minnesota%20U.%2C%20Theor.%20Phys.%20Inst.%22&ln=en" style="color: #6699cc; text-decoration: none;">Minnesota U., Theor. Phys. Inst.</a>), <a class="authorlink" href="http://inspirehep.net/author/profile/Omura%2C%20Yuji?recid=1376004&ln=en" style="color: #6699cc; text-decoration: none;">Yuji Omura</a> (<a class="afflink" href="http://inspirehep.net/search?cc=Institutions&p=institution:%22KMI%2C%20Nagoya%22&ln=en" style="color: #6699cc; text-decoration: none;">KMI, Nagoya</a>). Jun 12, 2015. 17 pp.<br />IPMU15-0083, FTPI-MINN-15-31<br />e-Print: <b><a href="http://arxiv.org/abs/arXiv:1506.03931" style="color: #6699cc;">arXiv:1506.03931</a> [hep-ph] | <a href="http://arxiv.org/pdf/1506.03931.pdf" style="color: #6699cc;">PDF</a></b></small><br />
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<li><a href="http://inspirehep.net/record/1376004/references" style="color: #6699cc;">References</a> | <a href="http://inspirehep.net/record/1376004/export/hx" style="color: #6699cc;">BibTeX</a> | <a href="http://inspirehep.net/record/1376004/export/hlxu" style="color: #6699cc;">LaTeX(US)</a> | <a href="http://inspirehep.net/record/1376004/export/hlxe" style="color: #6699cc;">LaTeX(EU)</a> | <a href="http://inspirehep.net/record/1376004/export/hlxh" style="color: #6699cc;">Harvmac</a> | <a href="http://inspirehep.net/record/1376004/export/xe" style="color: #6699cc;">EndNote</a></li>
<li><a href="http://adsabs.harvard.edu/cgi-bin/basic_connect?qsearch=arXiv:1506.03931" style="color: #6699cc;">ADS Abstract Service</a></li>
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<span class="moreinfo" style="background-attachment: initial; background-clip: initial; background-image: initial; background-origin: initial; background-position: initial; background-repeat: initial; background-size: initial;"><a class="moreinfo" href="http://inspirehep.net/record/1376004?ln=en" style="background-attachment: initial; background-clip: initial; background-image: initial; background-origin: initial; background-position: initial; background-repeat: initial; background-size: initial; color: #006600;">Detailed record</a></span><span class="moreinfo" style="background-attachment: initial; background-clip: initial; background-image: initial; background-origin: initial; background-position: initial; background-repeat: initial; background-size: initial;"> - <a class="moreinfo" href="http://inspirehep.net/search?ln=en&p=refersto%3Arecid%3A1376004&sf=earliestdate&rm=citation" style="background-attachment: initial; background-clip: initial; background-image: initial; background-origin: initial; background-position: initial; background-repeat: initial; background-size: initial; color: #006600;">Cited by 26 records</a></span></div>
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