Dynamical flavour dependence of static heavy meson decay constants on   the lattice
  We study the dynamical flavour dependence of the lattice estimates of the heavy meson decay constant in the static limit. We perform the analysis by considering negative flavour numbers and by extrapolating the results to positive values. We observe a sizeable flavour dependence which increases the quenched estimates. 
G.M. de Divitiis, R. Frezzotti, M. Masetti and R. Petronzio