[Theory-seminars] Theory seminar. Monday. L102 1pm. Rod Crewther

[Alessandro Pilloni]

Theory seminar
Monday, Jan 25, 2016
1:00 p.m.
CEBAF Center, Room L102

Rod Crewther
University of Adelaide

Title: Chiral-Scale Perturbation Theory and the Renormalization Group

Abstract: Three-flavor chiral perturbation theory with t,b,c quarks 
decoupled tests
the infrared limit of three-flavor QCD. The standard theory chiPT_3
(before being unitarised) assumes that there is no infrared fixed point
alpha_IR. If alpha_IR exists, we get chiral-scale perturbation theory
chiPT_sigma about a scale-invariant theory where the quark condensate is
also a scale condensate with nine Nambu-Goldstone (NG) bosons: a massless
0^{++} dilaton sigma (f_0(500) in the real world) as well as pi, K, eta.
Unlike electroweak and gravitational "dilatons", this dilaton is of the
original type: in the scale-invariant limit, the vacuum breaks scale
invariance and non-NG particles such as baryons retain their masses. The
effective Lagrangian for chiPT_sigma is the standard one modified by
sigma-dependent terms and factors required to give the correct dimensions,
and can be systematically extended to include higher-order and electroweak
corrections. The most important result is a neat explanation of the Delta
I = 1/2 puzzle for kaon decays; we propose to test it on the lattice via K
--> pi with both on shell. The dynamical electroweak analogue of our
dilaton yields a Higgs boson with a small mass proportional to beta'(4 +
beta'), where beta' is the slope of the beta function at the infrared
fixed point.

Prof. Crewther will be in JLab until Jan 31