Tuesday, 27 May 2014

Planck 2014 Liveblog: Day Two Session 2

Second plenary session.

11:00 am: Neutrinos, Dark Matter and Planck, Julien Lesgourges

Planck gives upper limit on neutrino mass from contribution to radiation and matter densities.  Effects on power spectra and large scale structure.  Expect to probe even minimal neutrino masses with combined Planck + Euclid data.  Timescale of ~ 10 years.

Effective number of neutrino species: with more data, preferred value increases from 3.  Would be "nearly" proved if BICEP2 stands up to scrutiny.  Neff > 3 and Mν > 0 make cosmology sensitive to mass splittings.  Neff > 3 not explainable by neutrino chemical potentials and standard neutrino sector, given measured mixing angles.

CMB best probe of DM: 44σ detection.  However, essentially no constraints beyond that.  In future CMB can probe DM annihilation/decay, plus scattering off non-DM species.  Has limited probe of warm/cold and of self interactions.

Annihilation/decay sensitivity mostly to polarisation data.  So far not much better than WMAP, but will change soon.

11:30 am: Hunting Down the Origin of Neutrino Masses: from Sterile Neutrinos to Baryon Number Violation, Andre de Gouvea

Main lessons of last 20 years: neutrino masses are small, and lepton mixing is "weird".  Also the question of the "desert" between the electron and neutrino, especially compared to the region between the electron and top.

Neutrino masses must come from EWSB, but interestingly do not need to be generated in the same way as other fermions.  Essentially three possibilities:
  1. Same source as other fermions (Dirac)
  2. Different Higgs (Majorana)
  3. Different mass scale (Majorana)
Simplest extension of SM: dimension-5 Weinberg operator.  Leads to see-saw mechanism.

Right-handed neutrino mass is 'tHooft natural: breaks U(1)B-L.

High-scale see-saw is popular but effectively untestable.  So ignore it from here on.

Right-handed neutrino masses forbidden between 1 and 10-9 eV, but allowed elsewhere.

Another low-scale possibility: loop-generated model.  Once you have lepton number violation, will always generate Majorana neutrino masses at some loop.  Models have the nice effect that many of them are testable.

What about baryon number violation?  Generically the case in GUTs; when we integrate out fields to generate LNV operators, we must generate BNV operators with related mass dimension.  Can prove (for operators not generated by gauge field) that important operators have odd mass dimension.  Lower limit at dimension-5, upper limit (from proton decay) at dimension-9.

Problem: GUT breaking before integrating out B-L operators, which means coefficients of BNV and LNV terms are not the same.  Still, expect similar order (BUT see doublet-triplet splitting problem).

Generally, most operators ruled out by proton decay but the induced decays are not standard.

12:00 am: New Physics Effects in Anomalous Gauge Boson Couplings, Gero Freiherr von Gersdorff

Precision experiments an important and complementary means to test the SM.  Gauge boson self-couplings predicted by gauge theory, can be modified by high-dimensional operators.  Focus on neutral gauge boson quartics, as not present (at tree level) in SM.  Generated first at dimension 8.

Terms involving photon grow strongly with energy, as must involve field strength.  Thus more accessible at LHC than at LEP, despite the proems with the LHC for precision.  Another advantage: sensitivity to diffractive events, where protons remain intact.  Photons can have energies up to ~ 1 TeV.

Problem with EFT: breaks down at LHC for couplings not very large; LHC sensitive to much larger couplings (by 4 or 5 orders of magnitude).

This surely demands considering explicit models to say anything?  Offered models are still non-renormalisable, dimension-5 couplings of photons.  Though operator scale now better, but still marginal (few TeV).

Generation from renormalisable  theories via loops; sensitivity to high-spin fields, multiplicity enhancement.

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