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Theory Center Seminar<br>
Monday, Jan. 25, 2016<br>
1:00 p.m. (coffee at 12:45 p.m.)<br>
CEBAF Center, Room L102<br>
<br>
Rod Crewther<br>
University of Adelaide<br>
<br>
<b>Chiral-Scale Perturbation Theory and the Renormalization Group</b><br>
<br>
Three-flavor chiral perturbation theory with t,b,c quarks decoupled
tests the infrared limit<br>
of three-flavor QCD. The standard theory chiPT_3 (before being
unitarised) assumes that there<br>
is no infrared fixed point alpha_IR. If alpha_IR exists, we get
chiral-scale perturbation theory<br>
chiPT_sigma about a scale-invariant theory where the quark
condensate is also a scale condensate<br>
with nine Nambu-Goldstone (NG) bosons: a massless 0^{++} dilaton
sigma (f_0(500) in the real <br>
world) as well as pi, K, eta. Unlike electroweak and gravitational
"dilatons", this dilaton is of the <br>
original type: in the scale-invariant limit, the vacuum breaks scale
invariance and non-NG particles <br>
such as baryons retain their masses. The effective Lagrangian for
chiPT_sigma is the standard one <br>
modified by sigma-dependent terms and factors required to give the
correct dimensions, and can <br>
be systematically extended to include higher-order and electroweak
corrections. The most important<br>
result is a neat explanation of the Delta I = 1/2 puzzle for kaon
decays; we propose to test it on the <br>
lattice via K --> pi with both on shell. The dynamical
electroweak analogue of our dilaton yields a Higgs<br>
boson with a small mass proportional to beta'(4 + beta'), where
beta' is the slope of the beta function <br>
at the infrared fixed point.
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