Two-Flavor Lattice-QCD Simulation in theϵRegime with Exact Chiral Symmetry

We perform lattice simulations of two-flavor QCD using Neuberger's overlap fermion, with which the exact chiral symmetry is realized at finite lattice spacings. The $ϵ$ regime is reached by decreasing the light quark mass down to 3 MeV on a 16³×32 lattice with a lattice spacing ~0.11 fm. We find a good agreement of the low-lying Dirac eigenvalue spectrum with the analytical predictions of the chiral random matrix theory, which reduces to the chiral perturbation theory in the $ϵ$ regime. The chiral condensate is extracted as ΣMS̄(2 GeV)=(251±7±11 MeV)³, where the errors are statistical and an estimate of the higher order effects in the $ϵ$ expansion.