[Jlab-seminars] Theory Center Seminar

[Mary Fox]

Theory Center Seminar
Monday, Jan. 25, 2016
1:00 p.m. (coffee at 12:45 p.m.)
CEBAF Center, Room L102

Rod Crewther
University of Adelaide

*Chiral-Scale Perturbation Theory and the Renormalization Group*

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.
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