Rare FCNC radiative leptonic B_(s,d) → γl~ + l~ ? decays in the standard model

摘要

We revisit rare radiative leptonic decays B_(s,d) → γe~+e~? andB_(s,d) → γμ~+μ~? in the standardmodel and provide the updated estimates for various differential distributions (the branching ratios, the forward-backward asymmetry, and R_(μ/e), the ratio of the differential distribution for muons over electrons in the final state). The newingredients of this work compared to the existing theoretical analyses are the following: (i)we calculate all B_d → γ and B_s → γ form factors induced by the vector, axial-vector, tensor and pseudotensor quark currents within the relativistic dispersion approach based on the constituent quark picture; (ii) we perform a detailed analysis of the charm-loop contributions to radiative leptonic decays: we obtain constraints imposed by electromagnetic gauge invariance and discuss the existing ambiguities in the charmonia contributions.