## 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]