QCD Topological Susceptibility from the Nonlocal Chiral Quark Model

We investigate the quantum chromodynamics (QCD) topological susceptibility. by using the semi-bosonized nonlocal chiral-quark model (SB-NL(X)QM) for the leading large-N-c contributions. This model is based on the liquid-instanton QCD-vacuum configuration, in which SU(3) flavor symmetry is explicitly broken by the finite current-quark mass (m(u), (d), m(s)) approximate to (5, 135) MeV. To compute X, we derive the local topological charge-density operator Q(t) (x) from the effective action of SB-N(X)QM. We verify that the derived expression for X in our model satisfies the WittenVeneziano (WV) and the Leutwyler-Smilga (LS) formulae, and the Crewther theorem in the chiral limit by construction. Once the average instanton size and the inter-instanton distance are fixed with (p) over bar= 1/ 3 fm and (R) over bar = 1 fm, respectively, all the other parameters are determined self-consistently within the model. We obtain X = (167.67MeV)(4), which is comparable with the empirical value X = (175 +/- 5MeV) 4 whereas it turns out that.QL = (194.30MeV) 4 in the quenched limit. Thus, we conclude that the value of. will be reduced around 10 similar to 20% by the dynamical-quark contribution.