Tuesday, 26 May 2015

Planck 2015 Liveblog: Day Two Session Two

We progress to the second day of the conference.  I decided to skip the first session of the morning, as none of the talks interested me and I'm still writing my talk.  The second session, however, has some stuff on neutrinos and unification that could be interesting.

11:30 am: ???,???

I missed the start of this talk ... but I think they might have changed the order, because this seems to be another string talk.  This is the kind of information it would be useful to put on the conference webpage, you know.

12:10 pm: "Unified Models of Neutrinos, Flavour and CP Violation", S King

Oh look, the previous talk ran long.  What a surprise.  It's not like that's been a serious problem already at this conference or anything.

PMNS matrix has 9 new parameters over "old" SM.  Split as three angles, quite well measured; three masses, two differences measured; and potentially three phases, hint for CP phase.

Flavour question: what is origin of quark and neutrino mass and mixing structures?  Address in GUTs, with flavour symmetries.   GUTs usual stuff based on subgroups of E6; flavour symmetries often subgroups of SU(3), including discrete groups like S4 and A4.

Digression: Klein symmetry.  If lepton mass matrix diagonal, it has phase symmetry T ~ diag (1, w2, w) with w a root of unity.  Symmetry of the Majorana matrix (when charged lepton matrix diagonal) depend on PMNS matrix.  These symmetries form the Klein group, Z2 x Z3.

Idea is that when flavour symmetry is broken, generators of Klein symmetry preserved differently between charged and neutral lepton sectors.  (Based on different flavon fields.)  This idea was popular as it gave tribimaximal mixing, so these are now in trouble with the observation of non-zero reactor mixing.  Mut go to larger symmetries Δ(6n2) which predict vanishing Dirac phase.

Semi-direct models use smaller groups where Klein symmetries are only partly preserved.  Three choices for which generators are broken.  Can get predictions for sum rules unless all generators broken.

CP violation can be handled with a new symmetry, and again a choice in how it is broken.  The simplest choices all predict the Dirac CP phase to be zero or maximal.  Some discussion of a "consistency condition" as being important; this is just a statement of group representations.  Also have indirect models with smaller groups.

Talking about a specific model, this is the drawback of the conference talk.  This talk could easily have spent more time on the details here, I'm getting the rough idea but the details are passing me by.  Seems to be able to use two right-handed neutrinos and three input parameters to get neutrino mass matrix and leptogenesis.  Further mention of extension to SUSY GUT.

Okay, this talk has too much stuffed in to the end of it, and once again is running long.  You can't talk about five(!) models in two minutes and say anything meaningful.

12:45 pm: "Current Status of the T2K Experiment", Yuichi Oyama

A second experiental talk!  T2K has been running for 6 years now, with a beam distance of just under 300km (to SuperK).  Beam is high-purity νμ.

Yet another problem with environmental noise.  They've closed the doors at the rear of the auditorium to block out the noise of people talking, not entirely successfully it must be said.  But a lot of people have left this talk and let the doors bang shut instead of closing them quietly.

T2K uses near (ND280) and far detectors to measure initial and final neutrino fluxes.  Detectors 2.5 degree off-axis; peak beam energy 0.6 GeV.  High energy neutrino flux suppressed.  Total luminosty has reached 1020 protons on target.  This splits 70/30 between neutrinos/anti-neutrinos.  Search for electron neutrino appearance.

Calibration of pion/kaon production using CERN NA61/SHINE experiment operating at same proton beam energy.  So should be highly trustworthy.  Use near/far detector correlations to control SuperK systematics.  (Factor of four improvement.)

Unambiguous observation of νμe deficit/surplus compared to no oscillation.  Measure θ23 to 10% level.  Also measure θ13 to slightly worse accuracy (hierarchy dependent).  Better agreement with normal hierachy, though still not fully discriminatory.  Also points to Dirac CP phase -90 degrees.

Test of CP using anti-neutrino beam.  Measures sign of CP phase positive/negative based on whether oscillation is stronger/weaker than for neutrinos.  Starting taking data June 2014.  Preliminary results for anti-νμ disappearance show consistency with neutrino data.  Work on anti-νe appearance ongoing.

Confidence for rejecting inverted hierarchy?  None; just a hint.
Prospects for improving CP phase? Needs several years to really get results.

1:20 pm: "Unification after Run 1 at LHC", Stuart Raby

We didn't change the schedule; we are over 45 minutes behind schedule.  That's just fucking absurd.  Also, this talk is another SUSY GUT talk, based on SO(10).  I missed the start of this talk, and of course I can't check the slides to see what I missed, so I'm not sure where this is going or what the assumptions are/point is.  Oh wait, an outline has shown up at 6 or 7 slides in.

Use SM masses and GUT structure, Yukawa unification (in third family) to predict SUSY spectrum.  Turns out that same GUT-scale boundaries will also automatically push first two generations of sfermions heavy.  All seems to follow the usual SUSY GUT structure, i.e. fit a lot of data and show that it is possible to be consistent.  Postdict a lot of stuff.  Theory does have Froggatt-Nielsen flavour fields, that's not always there.  Preference for a mass parameter at 25 TeV over higher values, not entirely sure why.

Predicts relatively light gluino (less than 2 TeV; LHC reach to 1.9 TeV).  μ to eγ observable in near future.

Fine tuning suggests boundary conditions should have physical meaning.

Large chi-squared per degrees of freedom.  Problem? Yes but not serious because ...
DM relic abundance/search constraints?  Not done yet.  Expect, based on older work, OK but to check.
LHC B-physics anomalies?  No better than SM.
Most significant implication of family symmetry?  Puts first two families in doublet, third in singlet.
Embed in higher flavour symmetry?  Possibly, but can be string motivated even if not.

No comments:

Post a Comment