We calculate the leptonic decay constants of B_{(s)} and D_{(s)} mesons in lattice QCD using staggered light quarks and Fermilab bottom and charm quarks. We compute the heavy-light meson correlation functions on the MILC asqtad-improved staggered gauge configurations which include the effects of three light dynamical sea quarks. We simulate with several values of the light valence- and sea-quark masses (down to ~m_s/10) and at three lattice spacings (a ~ 0.15, 0.12, and 0.09 fm) and extrapolate to the physical up and down quark masses and the continuum using expressions derived in heavy-light meson staggered chiral perturbation theory. We renormalize the heavy-light axial current using a mostly nonperturbative method such that only a small correction to unity must be computed in lattice perturbation theory and higher-order terms are expected to be small. We obtain f_{B^+} = 196.9(8.9) MeV, f_{B_s} = 242.0(9.5) MeV, f_{D^+} = 218.9(11.3) MeV, f_{D_s} = 260.1(10.8) MeV, and the SU(3) flavor-breaking ratios f_{B_s}/f_{B} = 1.229(26) and f_{D_s}/f_{D} = 1.188(25), where the numbers in parentheses are the total statistical and systematic uncertainties added in quadrature.
@article{arxiv.1112.3051,
title = {B- and D-meson decay constants from three-flavor lattice QCD},
author = {A. Bazavov and C. Bernard and C. M. Bouchard and C. DeTar and M. Di Pierro and A. X. El-Khadra and R. T. Evans and E. D. Freeland and E. Gamiz and Steven Gottlieb and U. M. Heller and J. E. Hetrick and R. Jain and A. S. Kronfeld and J. Laiho and L. Levkova and P. B. Mackenzie and E. T. Neil and M. B. Oktay and J. N. Simone and R. Sugar and D. Toussaint and R. S. Van de Water},
journal= {arXiv preprint arXiv:1112.3051},
year = {2013}
}