4 research outputs found
S-parameter and vector decay constant in QCD with eight fundamental fermions
SU(3) gauge theory with eight massless fundamental fermions seems to be near
the conformal boundary, and is a candidate theory of walking technicolor. Along
the series of study by LatKMI collaboration using HISQ fermions, S-parameter
and vector decay constant, which provide important constraints in the model of
electroweak symmetry breaking, are calculated for this theory. Use of various
volumes allows a systematic investigation of finite volume effects. A strong
sensitivity of the S-parameter to the volume is found.Comment: 7 pages, 7 figures, Proceedings of the 33rd International Symposium
on Lattice Field Theory, July 14-18, 2015, Kobe, Japa
The reactions π π → π π and γ γ → π π in χ PT with an isosinglet scalar resonance
The lowest-lying resonance in the QCD spectrum is the isoscalar
meson, also known as the . We augment SU(2) chiral
perturbation theory (PT) by including the meson as an additional
explicit degree of freedom, as proposed by Soto, Talavera, and Tarr\'us and
others. In this effective field theory, denoted PT, the
meson's well-established mass and decay width are not sufficient to properly
renormalize its self energy. At another low-energy constant
appears in the dressed -meson propagator; we adjust it so that the
isoscalar pion-pion scattering length is also reproduced. We compare the
resulting amplitudes for the and
reactions to data from threshold through the
energies at which the -meson resonance affects observables. The
leading-order (LO) amplitude reproduces the -meson pole
position, the isoscalar scattering lengths and scattering
and data up to GeV.
It also yields a amplitude that obeys the Ward
identity. The value obtained for the polarizability is, however, only
slightly larger than that obtained in standard PT.Comment: 17 pages, 7 figures. This version, which will be published in
European Physical Journal A, contains clarification and more explanation of
several points, as well as additional reference