Calculation of long-distance effects in exclusive weak radiative decays of B-mesons

We calculate the contribution of the weak annihilation to the B → ϱγ decay amplitude by means of QCD sum rules using the photon light-cone wave function. We find that this long-distance contribution amounts to about 10% of the leading short-distance effect in B− → ϱ−γ. On the other hand, weak annihilation is the dominant source of the corresponding D meson decays and according to our estimates, yields branching ratios of O(10−4) for D0 → K∗0γ, O(10−5) for Ds → ϱ+γ, and O(10−6) for D− → ϱ−γ and for D0 → ϱ0γ. In addition, an estimate of the B → lνγ decay decay is obtained.