Light quark masses from lattice QCD

We present estimates of the masses of light quarks using lattice data. Our main results are based on a global analysis of ail the published data for Wilson, Sheikholeslami-Wohlert (clover), and staggered fermions, both in the quenched approximation and with n(f) = 2 dynamical flavors. We find that the values of masses with the various formulations agree after extrapolation to the continuum limit for the n(f) = 0 theory. Our best estimates, in the (MSS) over bar scheme at mu = 2 GeV, are (m) over bar = 3.4 +/- 0.4 +/- 0.3 MeV and m(s) = 100 +/- 21 +/- 10 MeV in the quenched approximation. The n(f) = 2 results, (m) over bar = 2.7 +/- 0.3 +/- 0.3 MeV and m(s) = 68 +/- 12 +/- 7 MeV, are preliminary. (A linear extrapolation in nf would further reduce these estimates for the physical case of three dynamical flavors.) These estimates are smaller than phenomenological estimates based on sum rules, but maintain the ratios predicted by chiral perturbation theory. The new results have a significant impact on the extraction of epsilon'/epsilon from the standard model. Using the same lattice data we estimate the quark condensate using the GeIl-MannOakes-Renner relation. Again the three formulations give consistent results after extrapolation to a = 0, andthe value turns out to be correspondingly larger, roughly preserving m(s)[(psi)over bar>psi>].