Tuesday, 24 May 2016

Planck 2016 Liveblog: Day Two Session One

We move to the second day of the conference, and the only plenary session of the day.  Which is fine by me, I like the format for the conference this year more than last year.  We have a selection of collider phenomenology talks, though the connections seem a bit limited to me.

09:00 am: Recent ATLAS results, Martine Bosman

Always good to start with an experimental talk.  It keeps us (me?) honest.  Though I'm a little surprised we don't have talks from both ATLAS and CMS on the same day (CMS talk tomorrow).

Ongoing efforts to rediscover the SM at 13 TeV.  Small excess in WW/WZ production, but might be resolved with improved theoretical predictions.  New top mass measurements push errors from ATLAS alone to less than 1 GeV.

Higgs physics: legacy of half a million produced at run 1, of which e.g. 1000 decayed to diphotons, 65 to the golden channel, or 30000 to ditau.  ATLAS alone in excess of 5σ in γγ, ZZ and WW channels; 4σ in ττ; less than 2σ in bb.  Higgs mass measurement still statistically dominated; improvements to come.  Observations at 13 TeV beginning.

Resonance searches boring except for the obvious one.  Clear from the likelihood plots in the mass-width plane that the width is poorly constrained by the ATLAS 13 TeV data; might not be true at 8 TeV, but this is not clearly shown here.

SUSY searches at 13 TeV already pushing exclusions into new ground, e.g. 1.5 TeV gluino.  Small excess in dilepton channel at 8 TeV seems to be persisting so far, but the significance is not very big.  Still, definitely something to watch out for.

09:30 am: Is supersymmetry still alive? Werner Porod

The title is a question, so the answer is no.  Another person who didn't feel any need to put their talk online in advance.

Before the LHC, the usual approach was to try and fit all low-energy data with something like CMSSM or mSUGRA.  This pointed to light sfermions below a TeV.  Of course, that hasn't happened.  Additionally, the Higgs has changed from a search target to a precision observable that NP must explain.  This is the well-known MSSM challenge for the Higgs mass, with radiative corrections of nearly 100%.  In minimal GMSB, for example, the stops are forced too heavy to be seen at the LHC.

You can do new fits if you want.  It gives what you'd expect, namely preferred points just above the limits.  Also, if you include the muon anomalous magnetic moment, then the CMSSM is actually excluded at 90%.   Even if you ignore that, you run into problems with charge/colour breaking minima.  Not impossible but you're sitting no the boundaries.

A similar thing can happen in Natural SUSY.  Light stops are allowed by observation, but if the gluino is also heavy it will tend to run to a CCB minima before the GUT scale.

If stops and gluinos are heavy, only Higgsinos are light, difficult to see.  DM relic density too low but can't be excluded, or discovered with Xenon 1T.  Can do something with monojets at LHC up to maybe 250 GeV exclusion.  So this will live for some time, it seems.

Extended gauge groups based on SO(10) or E8 have two effects.  Tree-level contribution to Higgs mass increased, so smaller radiative corrections needed; and have right-handed sneutrinos that can be DM.

Anomalies?  That's what right-handed neutrinos are for.
Gluino bounds and fine tuning?  ...
Generalised GMSB can have lighter stops at TeV scale?  What of CCB?  Seems not to be resolved here either.

10:00 am: Higgs LFV decays, Antonio Delgado

Mild excess (2.4σ at most) in h → μτ.  However, this is for all intents and purposes zero in the SM.  Interestingly, this corresponds to a LFV Yukawa Yμτ Yτμ ~ mμ mτ/v2.  The challenge is to induce this decay without inducing LFV decay of leptons above the strict bounds.  In a simple SM EFT, the latter exclude the former.  This suggests going to a model with more than one source of EWSB.

First effort: SUSY with LFV soft terms (slepton masses and A-terms).  Need large A-terms relative to slepton masses to get a large enough rate, which runs into charge-breaking vacua.

Second effort: vector-like fermions.  Use four-fermion operator as source of LFV.  Leads to fermion masses in the 10 TeV range, with 20 TeV cut-off of dimension 6 operator.  This can be weakened; there are three possible fermion contractions, and only one generates τ → μγ.  Taking that one to be zero is unstable under the RGE, but suggests you could have a moderate suppression.

Non-SUSY 2HDMs? Easy?  Depends, but typically one tends to be heavy.
Muon g-2? Not considered in this study.
Debate rising over EFT allowed or not.

10:30 am: CP Violation and Invisible Higgs Decays at the LHC, Jorge Romao

2HDM with usual softly-broken Z2 has, in general, irreducible complex phase.

You know, it's rare to see a speaker completely skip any motivation for their work.

I guess there's no problem in computing the bounds on these models, it's just all a bit meh.

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