Results for light pseudoscalars from three-flavor simulations

We compute pseudoscalar meson masses and decay constants in partially quenched QCD with three dynamical flavors of improved staggered quarks. Fitting the lattice data to staggered chiral perturbation theory (SχPT) forms and extrapolating in quark mass and lattice spacing, we find: fπ=129.5+/-0.9+/-3.5 MeV, fK=156.6+/-1.0+/-3.6 MeV, and fK/fπ=1.210(4)(13). The value for fK/fπ implies |Vus|=0.2219(26). We also obtain mu/md=0.43(0)(1)(8), or, with more input on electromagnetic (EM) effects from the continuum, mu/md=0.41(0)(1)(4). Using the one-loop perturbative mass renormalization [Phys. Rev. D 70 (2004) 031504(R)], we determine mu and md in the MS scheme