Enhanced Electromagnetic Corrections to the Rare Decay Bs,d →μ+μ-

We investigate electromagnetic corrections to the rare B-meson leptonic decay Bs,d→μ+μ- from scales below the bottom-quark mass mb. Contrary to QCD effects, which are entirely contained in the B-meson decay constant, we find that virtual photon exchange can probe the B-meson structure, resulting in a "nonlocal annihilation" effect. We find that this effect gives rise to a dynamical enhancement by a power of mb/ΛQCD and by large logarithms. The impact of this novel effect on the branching ratio of Bs,d→μ+μ- is about 1%, of the order of the previously estimated nonparametric theoretical uncertainty, and four times the size of previous estimates of next-to-leading order QED effects due to residual scale dependence. We update the standard model (SM) prediction to B(Bs→μ+μ-)SM=(3.57±0.17)×10-9.