Neutral B meson mixing in unquenched lattice QCD

We study B-d and B-s mixing in unquenched lattice QCD employing the MILC Collaboration gauge configurations that include u, d, and s sea quarks based on the improved staggered quark (AsqTad) action and a highly improved gluon action. We implement the valence light quarks also with the AsqTad action and use the nonrelativistic NRQCD action for the valence b quark. We calculate hadronic matrix elements necessary for extracting Cabibbo-Kobayashi-Maskawa matrix elements from experimental measurements of mass differences Delta M-d and Delta M-s. We find xi equivalent to f(Bs)B(Bs)/f(Bd)B(Bd)=1.258(33), f(Bd)B(Bd)=216(15) MeV, and f(Bs)B(Bs)=266(18) MeV. We also update previous results for decay constants and obtain f(Bd)=190(13) MeV, f(Bs)=231(15) MeV, and f(Bs)/f(Bd)=1.226(26). The new lattice results lead to updated values for the ratio of Cabibbo-Kobayashi-Maskawa matrix elements |V-td|/|V-ts| and for the standard model prediction for Br(B-s ->mu(+)mu(-)) with reduced errors. We determine |V-td|/|V-ts|=0.214(1)(5) and Br(B-s ->mu(+)mu(-))=3.19(19)x10(-9).