Pure Leptonic Radiative Decays $B^{\pm },D_s\to \mathrm{\ell }\nu \gamma$ and the Annihilation Graph

Pure leptonic radiative decays of heavy-light mesons are calculated using a very simple non-relativistic model. Dominant contribution originates from photon emission from light initial quark. We find $BR(B^{\pm }\to \mathrm{\ell }\nu \gamma )\sim 3.5\times {10}^{-6}$ and $BR(D_s\to \ell\nu\gamma)\sim1.7 \times10^{-4}$. The importance of these reactions to clarify the dynamics of the annihilation graph is emphasized.