Calculation of Long-Distance Effects in Exclusive Weak Radiative Decays of B-Mesons

Abstract

We calculate the contribution of the weak annihilation to the $B\rightarrow ργ$ 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 $B^-\rightarrow ρ^-γ$. 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 $D^0\rightarrow \bar{K}^{*0}γ$, $O(10^{-5})$ for $D_s\rightarrow ρ^+γ$, and $O(10^{-6})$ for $D^-\rightarrow ρ^-γ$ and for $D^0\rightarrow ρ^0γ$.