Decay constants of B-mesons from non-perturbative HQET with two light   dynamical quarks
  We present a computation of B-meson decay constants from lattice QCD simulations within the framework of Heavy Quark Effective Theory for the b-quark. The next-to-leading order corrections in the HQET expansion are included non-perturbatively. Based on Nf=2 gauge field ensembles, covering three lattice spacings a (0.08-0.05)fm and pion masses down to 190MeV, a variational method for extracting hadronic matrix elements is used to keep systematic errors under control. In addition we perform a careful autocorrelation analysis in the extrapolation to the continuum and to the physical pion mass limits. Our final results read fB=186(13)MeV, fBs=224(14)MeV and fBs/fB=1.203(65). A comparison with other results in the literature does not reveal a dependence on the number of dynamical quarks, and effects from truncating HQET appear to be negligible. 
F. Bernardoni, B. Blossier, J. Bulava, M. Della Morte, P. Fritzsch, N.   Garron, A. G\'erardin, J. Heitger, G. von Hippel, H...
hep-lat hep-ph