Sigma resonance parameters from Lattice QCD

Speaker: Raquel Molina, IF-USP

When/Where: 4:30 PM, April 18, 2018 (Sala F-210)

Abstract: The lightest excited state in the spectrum of hadrons is at
the same time one of the most controversial. The sigma meson
properties (mass and width) and even presence were debated for a long
time. Recently, the GWU group has conducted a two-flavor (N_f = 2)
lattice QCD calculation of the elastic phase-shifts for pion-pion
scattering in the scalar, isoscalar channel. The calculation has been
performed for two quark masses corresponding to pion masses of 227 MeV
and 315 MeV. The sigma-meson parameters are extracted using various
parametrizations of the scattering amplitude, such as conformal ones,
and others based on chiral symmetry and general properties of the
scattering amplitude (unitarity). The latter allows to conduct
extrapolations to the physical point, where the result for the pole
position reads M (sigma) = (440(13)(50) – i 240(20)(25)) MeV. The
several lattice simulations enable to investigate the behavior of the
sigma-meson parameters with increasing pion mass in the chiral unitary
approach, which is discussed as well.