We perform a precise calculation of the chiral condensate in QCD using
lattice QCD with 2+1 flavors of dynamical overlap quarks. Up and down quark
masses cover a range between 3 and 100 MeV on a 16^3x48 lattice at a lattice
spacing around 0.11 fm. At the lightest sea quark mass, the finite volume
system on the lattice is in the epsilon-regime. By matching the low-lying
eigenvalue spectrum of the Dirac operator with the prediction of chiral
perturbation theory at the next-to-leading order, we determine the chiral
condensate in 2+1-flavor QCD with strange quark mass fixed at its physical
value as Sigma (MS-bar at 2 GeV) = [242(04)(^+19_-18}) MeV}]^3, where the
errors are statistical and systematic, respectively.Comment: 4 pages, 3 figures, errors in table 1 and fig.3 corrected. Published
in PR
