Scalar susceptibility from the instanton vacuum with meson-loop corrections

The scalar susceptibility (χs) of QCD, which represents the response of the chiral condensate to a small perturbation of explicit chiral-symmetry breaking (m≠0), is investigated within the nonlocal chiral quark model (NLχQM) based on the instanton vacuum configuration for Nf=2. We also take into account 1/Nc 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 χs=-0.34 GeV2 with the ML corrections and 0.18 GeV2 without it. From these observations, we conclude that the ML corrections play an important role in the presence of finite current-quark mass.