Chiral corrections and lattice QCD results for fBs/fBd and ΔmBs/ΔmBd

It has been argued recently that the inclusion of the chiral logarithms in extrapolation of the lattice data can shift the value of the hadronic parameter ξ=fBsBBs/fBdBBd, from 1.16(6) to 1.32(10) and even higher. If true, that would considerably change the theoretical estimate for the ratio of oscillation frequencies in the B0s- and B0d-systems, and would affect the standard CKM unitarity triangle analysis. In this Letter we show that fBs/fBd≈fK/fπ, and thus the uncertainty due to the missing chiral logs is smaller than previously thought. By combining the NLO chiral expansion with the static heavy quark limit we obtain ξ=1.22(9).