Scalar susceptibility from the instanton vacuum with meson-loop corrections

TL;DR

This paper investigates the scalar susceptibility in QCD using a nonlocal chiral quark model based on the instanton vacuum, highlighting the significant impact of meson-loop corrections near zero quark mass.

Contribution

It introduces meson-loop corrections into the instanton vacuum-based model to accurately compute scalar susceptibility in QCD.

Findings

ML corrections significantly alter the chiral condensate near zero quark mass

Scalar susceptibility with ML corrections is -0.34 GeV^2

Without ML corrections, scalar susceptibility is 0.18 GeV^2

Abstract

The scalar susceptibility (chi_s) of QCD, which represents the response of the chiral condensate to a small perturbation of explicit chiral-symmetry breaking, is investigated within the nonlocal chiral quark model (NLchiQM) based on the instanton vacuum configuration for N_f = 2. We also take into account 1/N_c meson-loop (ML) corrections including scalar and pseudoscalar mesons. It turns out that the chiral condensate is modified to a large extend by the ML corrections in the vicinity of m = 0, whereas its effect becomes weak beyond m ~ 100 MeV. As numerical results, we find that chi_s = -0.34 GeV^2 with the ML corrections and 0.18 GeV^2 without it, respectively. From these observations, we conclude that the ML corrections play an important role in the presence of finite current-quark mass.