Friday, 25 September 2015

Friday 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...

  • There is an article at Quanta Magazine constructed around a profile of Nima Arkani-Hamed 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.
  • A few things wrapped up for me this week...

    (1) Uploaded to the arXiv v2 of a paper on displaced Higgs decays (see blog from back in June). In particular, the new version has the plots updated and include some recent results. 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.

    (2) Uploaded to the arXiv a conference proceedings (PLANCK) summarising two recent papers: "How to avoid unnatural hierarchical thermal leptogenesis." 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 blog post 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...

    (3) Uploaded an arXiv preprint titled: "νDFSZ: a technically natural non-supersymmetric model of neutrino masses, baryogenesis, the strong CP problem, and dark matter." It is a rather short paper which contains an existence proof that weakly coupled high-scale physics can explain phenomenological shortcomings of the SM without introducing a naturalness problem. 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 earlier blog post! Let's be clear here: the model does not solve the big hierarchy problem; we don't explain where 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".

    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.
    • The Taller de Altas Energías 2015 School is currently ongoing (programme here).
      • Links without (too many) thinks:
        • Life and Physics from Jon Butterworth: "How the Higgs boson is born and how it dies: the most precise picture so far."
        • ATLAS Blogs: Part 2 of James Howarth's TOP2015 review.
        • The Conversation: "How we plan to bring dark matter to light," with a little on SUPL and SABRE.
        • Cosmos: "Ghost traps: the hunt 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...
      • In video/audio media:
        • In Particular Ep 3: Particle Zoo... what is your favourite particle? [35:15]
        • CERN: Timelapse video of the CERN Axion Solar Telescope (CAST) following the Sun [1:22], and a bit of noise rock in situ; Deerhoof vs. the Large Hadron Collider [9:05].
        • Waking Up with Sam Harris: The Multiverse & You (& You & You & You…), A Conversation with Max Tegmark. [1:26:42]
        • MinutePhysics: Why do we put telescopes in space? [2:20]
        • It's Okay to be Smart: Theory vs. Hypothesis vs. Law... Explained! [7:11]
        • Numberphile: Philosophy of Numbers. [9:40]

      Friday, 18 September 2015

      Friday 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...

      • It's the season for conferences! This week we have...
        • 8th International Workshop on Top Quark Physics (TOP2015: indicotwitter). One of the interesting new results includes evidence for (>3σ) single top quark production in the s-channel with the 8 TeV dataset. There's an entertaining review of the first two days here from James Howarth.
        • Particle Astrophysics and Cosmology Including Fundamental InteraCtions (PACIFIC 2015: agenda).
        • Corfu Summer Institute: 15th Hellenic School and Workshops on Elementary Particle Physics and Gravity (programme).
      • The second is an ATLAS diboson resonance search which combines the results from the large-R dijet channel with the leptonic channels. The results are well summed up by the first Figure in the Appendix:

        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 this 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 >30 extra citations to the original ATLAS paper since I made a quick literature survey 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...
      • The TAUP2015 parallel session slides 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 Slide 10 [pdf]). 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).

      • 32 Australian institutions have signed up to 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."
      • Links without thinks:
        • Institute for Advanced Study: "Beyond the Higgs: From the LHC to China."
        • Richard Dawid wrote a guest blog on the reference frame: "What confirms a physical theory?" This should be taken in the context of that Ellis/Silk nature comment article and the ensuing debate on post-empirical science.
        • New Scientist: "Black holes may be brick walls that bounce information back out." On 't Hooft's new contribution to the black hole information paradox...
        • ... and Sabine Hossenfelder's reaction at Starts With a Bang: "Black holes and academic walls."
        • Also at Starts With a Bang: "Will The LHC Be The End Of Experimental Particle Physics?"
      • Lastly, in images from space, it is hard to top these new images of Pluto!

      Saturday, 12 September 2015

      Friday 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...

      • The XIV International Conference on Topics in Astroparticle and Underground Physics (TAUP 2015) conference has been happening this week (hashtag here). The plenary talks are available but unfortunately a very many interesting parallel sessions are inaccessible...
      • 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 this document [pdf]. 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?

      • 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 recently by XENON100 (and now perhaps XMASS?). He posted to the arXiv last week outlining a scenario...

        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 diurnal (daily) modulation.

        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.
      • Further on the direct detection front, Lateral Mag have a story 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!
      • On this blog:
        • I have updated my thoughts 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...

          At least to me, the following definitions make sense: a hierarchy problem is an unexplained hierarchy of scales within a model, and; a naturalness problem (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 blogged about a month ago. Actually, taken this way, minimal supersymmetry alone doesn't solve the hierarchy problem (i.e. it has a mu problem). Nevertheless (and if it arises at the TeV scale) supersymmetry ensures that the electroweak scale does not have a naturalness problem whatever the theory of gravity, and whatever 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.
        • Playing with google charts recently I added a geomap and new/returning pageview charts using google analytics tracking, the google analytics superproxy, 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!
      • News from space...
        • A detailed image of the bright spot on Ceres...

        • ... and incredible new images of Pluto and Charon!

      Saturday, 5 September 2015

      Friday 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...

      • Conferences of interest this week include The 3rd Annual Large Hadron Collider Physics Conference (LHCP2015; indico; twitter), and QCD@LHC 2015 (indico).
      • At LHCP, Marco Pieri presented the brand new ATLAS+CMS Higgs combination (talk here [pdf]). Slides 17 and 18 tell the story for the SM Higgs versus the null:

        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 at Moriond) 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.
      • The Times Higher Education World University Rankings have decided to exclude 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.
      • According to this nature news 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.'"
      • Some movement on the Hawking/Perry/Strominger proposal for the black hole information loss problem. There's now a short stake-claiming arXiv paper, and an hour-long talk from Malcolm Perry on YouTube. Sabine Hossenfelder reacts here.
      • From CERN: a summary 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 recent scrubbing runs.
      • In video/audio media:
      • Lastly, here is an antineutrino global map: an experimentally informed model of Earth’s surface antineutrino flux over the 0 to 11 MeV energy spectrum.