Lattice QCD Study of $B$-meson Decay Constants from ETMC
  We discuss a lattice QCD computation of the $B$-meson decay constants by the ETM collaboration where suitable ratios allow to reach the bottom quark sector by combining simulations around the charm-quark mass with an exactly known static limit. The different steps involved in this ratio method are discussed together with an account of the assessment of various systematic effects. A comparison of results from simulations with two and four flavour dynamical quarks is presented. 
A. Bussone, N. Carrasco, P. Dimopoulos, R. Frezzotti, V. Gim\'enez, G.   Herdo\'iza, P. Lami, V. Lubicz, C. Michael, E. Picc...
hep-lat hep-ph