The XXV International Symposium on Lattice Field Theory

We determine the topological susceptibility χt in the trivial topological sector generated by lattice simulations of two-flavor QCD with overlap Dirac fermion, on a 163 × 32 lattice with lattice spacing ∼ 0.12 fm, at six sea quark masses mq ranging from ms/6 to ms (where ms is the physical strange quark mass). The χt is extracted from the plateau (at large time separation) of the time-correlation function of the flavor-singlet pseudoscalar meson (η ′), which arises from the finite size effect due to fixed topology. In the small mq regime, our result of χt is proportional to mq as expected from chiral effective theory. Using the formula χt = mqΣ/N f by Leutwyler-Smilga, we obtain the chiral condensate in N f = 2 QCD as ΣMS(2 GeV) = [254(5)(10)MeV]3, in good agreement with our previous result obtained in the ε-regime.