Topological susceptibility in two-flavor lattice QCD with exact chiral symmetry

Abstract

We determine the topological susceptibility χt in two-flavor QCD using the lattice simulations at a fixed topological sector. The topological charge density is unambiguously defined on the lattice using the overlap-Dirac operator which possesses exact chiral symmetry. Simulations are performed on a 163×32 lattice at lattice spacing ∼ 0.12 fm at six sea quark masses mq ranging in ms/6−ms with ms the physical strange quark mass. The χt is extracted from the constant behavior of the time-correlation of flavor-singlet pseudo-scalar meson two-point function at large distances, which arises from the finite size effect due to the 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/Nf by Leutwyler–Smilga, we obtain the chiral condensate in Nf=2 QCD as ΣMS¯(2 GeV)=[252(5)(10) MeV]3, in good agreement with our previous result obtained in the ϵ-regime.