Friday, 29 May 2015

Planck 2015 Liveblog: Day Five Session One

We come to the final day of the conference, and perhaps the most interesting one based on the talk titles.  We have one plenary session, not counting the conference summary.

9:00 am: "Neutrino Mixing 2015", G Altarelli

The last 15 years have seen much progress and discovery in the neutrino sector.  The existence of neutrino masses might, through the see-saw mechanism, point to high-scale physics.  But many important questions remain unanswered, both experimental (e.g. absolute scale of masses) and theoretical (e.g. theory of flavour).

For the absolute mass scale, Katrin, to start in Summer 2016, will reduce limits down to the eV-scale.  However, it would still be inferior to Planck limits (assuming standard cosmology).

After saying standard see-saw disfavours EW-scale neutrinos, admits those models must be "excluded experimentally, not ideologically".  After this conference that's a notable statement.

Measurement of θ13 makes it more promising to resolve neutrino hierarchy.

Existence of heavy right-handed neutrinos introduces hierarchy problem (stated here in terms of evolution of HIggs mass parameter across threshold).  Also worsen stability problem of Higgs vacuum, but will not make it unstable if mass is below 1014 GeV.

Discussion of νMSM and its efforts to solve all outstanding problems of SM at the EW scale.  Also of 3.5 keV line.

Various anomalies that might point to sterile neutrinos.  Cannot be thermal due to Planck constraints.  Reactor anomaly put into doubt by recent ab initio calculation; theoretical uncertainties seem to be of the order of the observed effect.

Flavour models cover range from anarchy to discrete groups.  Main problem for discrete groups is lack of evidence in quark sector.

See-saw mechanism source for discrete symmetries in lepton but not quark sector? Possible.

9:30 am: "Looking for New Naturally Aligned Higgs Doublets at the LHC", Apostolos Pilaftsis

Alignment here is referring to Higgs-gauge boson couplings.  In particular, tuning the quartic couplings to get the alignment limit between the angles β and α for arbitrary masses of the heavy Higgses.  Can this limit be found by using symmetries to set certain combinations of the quartics do vanish, so that the alignment quartic is trivial?

Approach to solve using bilinear formalism, rewriting potential in terms of quadratic in powers of vectors of Higgs bilinears.  Find there exist three choices of field symmetry that enforce the alignment condition.  e.g. most symmetric option is Sp(4) ~ SO(5).  Symmetries must be broken, softly by mass mixing and also by Yukawas.

10:00 am: "Towards Unification of GUT Families", Jihn E. Kim

Something with SU(7).  Flipped SU(5) there somewhere?  It was the banquet last night and I only had the one cup of coffee at breakfast.

SU(7) as SU(5) and flavour symmetries.  Not obvious to me how things all fit together, but apparently they can.  Trying to fit in string theory and get correct prediction for Weinberg model.

There are a lot of forumlae here.

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