Monday, 19 May 2014

Origins of Mass 2014: Day One, Session 2

Unlike places like Planck or Pheno, this conference works with a smaller number of longer talks.  Hence, we had only one talk in the pre-break morning session and have only two more before lunch.  Also unlike most other conferences, the talks don't seem to fit any obvious pattern.

10:20 am: The Origin of Mass and Lattice Quantum Dynamics, Laurent Lellouch

This guy has got into the swing of things with his title; disappointingly, he seems to be the only one.  This is lattice QCD, rather than strongly-interacting BSM.  Of course, most of the mass associated with the visible sector comes from QCD rather than the Higgs mechanism.

Additionally, nonperturbative QCD allows nucleosynthesis (while forbidding proton decay) so we have a complicated and subtle balance between strong, electromagnetic and quark-Higgs interactions.

Just shown a result plot including data from my office mate in TRIUMF.  One thing is that, thanks to him, a lot of this talk so far has been very familiar to me despite not working on lattices.

Lattice important for dark matter direct detection.  Computation of nucleon scattering from quark scattering done on lattice.  Two approaches, based on three-point functions (harder technically, gives result at leading order) or two-point functions (easier technically, gives result at subleading order in slope of spectrum).  Looking at the results shown, I am sceptical about the uncertainty on the extrapolated slopes.  Indeed, order-one uncertainty seems to exist.  Lattice is claiming ~30% but I have doubts.  Results smaller (for strange content) compared to previous non-lattice expectations.

Discussion of masses of up and down quarks.  Now that simulations can be done for physical pion masses, uncertainty drops to about 2%.  So good, that isospin symmetry breaking effects are becoming important.  More generally, such effects highly important in forbidding proton decay while allowing neutron decay, with all the implications for Big Bang nucleosynthesis.  Also, seems that lattice people not quite willing yet to abandon up-mass being zero (alternate solution to strong CP problem).

Two approaches: direct inclusion in non-perturbative computation, or perturbative expansion about isospin symmetric results.

Okay, looks like results don't agree with up-mass being zero.  Additionally, proton-neutron splitting comes from incomplete cancellation of QED and quark mass effects.  Is this really a fine tuning?  And if so, how severe is it?

11:10 am: Right-Handed Neutrinos as the Origin of the Electroweak Scale, Hooman Davoudiasl

This is based on a recent paper I read, found here.

The basis is the finite-naturalness idea of Strumia, or more rigorously on some type of conformal understanding of high energy physics.  We had a good talk on that at Pheno, so I link there.  This paper is not attempting to resolve this problem.  Rather, it is addressing a different question, about the possibility of heavy neutrinos giving neutrino masses through a see-saw mechanism.  In the simplest ideas, these masses already give too large a contribution to the Higgs mass from finite renormalisation effects.

Additionally, if we take a classically scale-invariant EW Lagrangian, then we cannot get the correct Higgs VEV through quantum effects.  Coupling to the right-handed neutrinos can solve this problem as well.

The problem is that to gain leptogenesis and sufficiently large neutrino masses, the expected Higgs mass parameter is close to 8 TeV, two orders of magnitude too large.

The model-building solution is to separate leptogenesis and neutrino masses, so that they come from different operators.  This is enforced through a global Z2 parity.  This leads to a second Higgs doublet, which is then a natural DM candidate (the inert doublet).  Neutrino masses now arise at one loop.

One-loop effects generate mass for inert doublet.  SM Higgs mass is generated at two loop.

This is not Hooman's best talk that I've seen.  Having read the paper, he seems to be going through it in a fairly dry fashion.

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