Wednesday, 25 May 2016

Planck 2016 Liveblog: Day Three Session One

Day Three already, and we have a full morning of plenary talks.  I might skip some of the afternoon talks today, as I have a lot of work to do; we'll see how I feel after lunch.  The theme for today would seem to be flavour.

09:00 am: Recent results from LHCb and future prospects, Arantza Oyanguren

Not good when the first talk starts late, but I reckon only about a quarter of attendees have shown up on time.

Interesting to start with a null result: exclusion of candidate tetraquark seen at D0.

No evidence for NP in Vub.  But this part of the talk didn't seem too convincing as a resolution of the discrepancy.

All discrepancies go away.

OK, something.  Decays in charm sector inconsistent with lepton universality at 4σ.

09:30 am: Possible Flavour Anomalies, Tobias Hurth

Focus on semi-leptonic penguin decays in B sector, in particular the question of how strong the need is for BSM to explain observations.

I got a little lost here.  Would have helped if the people behind me hadn't talked for several minutes.

OK, I think the general point was to use the EFT language to study various observables in a model-independent way.

10:00 am: Probing Flavour Dynamics at the LHC, Kaladi Babu

Please be interesting.

Discuss three explanations of flavour: at high scale within GUTs, radiatively, and with a low-scale gauge theory.

Within GUTs, consider SO(10) models.  This has an obvious connection to neutrino masses.  Two Higgses are needed/allowed, which leads to non-trivial connections between the quark and lepton Yukawa matrices.  However, it's not exactly impressive:
The model has 11 parameters plus 7 phases to fit 18 known observables.
Predictions are consistent with experiments.
When inputs and outputs are equal in number, that's not exactly a shocking result.  Most interesting point is that θ13 is in line with pre-existing predictions.  But then we move to other models based on different Higgs structure and some vector-like fermions:
Yukawa sector has 14 real parameters plus 8 phases to fit 18 measured flavour observables
More inputs than outputs, so you should be able to fit things.

Radiative models based on idea that 3rd generation Yukawas are tree-level, 2nd generation 1-loop suppressed and 1st generation are 2-loop suppressed.  Lightness of leptons can be explained by an additional loop suppression.  Need extra diquark/leptoquark scalars.  These states are what make things interesting, as they can be searched for.  Indirect bounds are not too severe, at TeV scale, so if they exist they might be within the reach of the LHC.

Models can be extended to include radiative generation of neutrino masses.  Upper limits on additional scalar masses; though allowed to be too heavy even for 100 TeV machine.  Still, possible probes based on LFV observables.

Flavour gauge models are based on gauging anomaly-free subgroups of SM flavour symmetry.  Several choices, but finite and smal set of models.  Need exotic Higgses to break gauge symmetry.  Yukawa structure comes from VEVs (overall scale remains free).  Some additional protections, depending on VEV structure, that is possible and allows flavour guage bosons to be at TeV scale.  I got a bit lost here.

Of course, TeV-scale scalars raises the possibility that the 750 GeV resonance could be explained this way.  Some effort needed to avoid Tevatron constraints.  Large coupling to photons comes from multiple charged Higgs present in model.  Moderately large quartics (~ Yukawas squared) needed; tension but not excluded.

10:30 am: Recent CMS Results, Joao Varela

The second general LHC talk.  Looking through the slides, it looks much like the ATLAS talk from yesterday.  To quote the conclusions:
Excesses from 8 TeV searches not (yet?) confirmed at 13 TeV
 Apart from the 750 GeV brouhaha, I think that's the main point really, isn't it.

No comments:

Post a Comment