Pure leptonic radiative decays B-+/-,D-s->l nu gamma and the annihilation graph

Pure leptonic radiative decays of heavy-light mesons are calculated using a very simple nonrelativistic model. For B-+/- the dominant contribution originates from photon emission from light initial quark. Emission of the photon overcomes the helicity suppression and leads to Br(B-+/- --> l nu gamma) similar to 3.5 x 10(-6) (which is about 16 times more than Br(B-+/- --> mu + v)). Also, we find Br(D-s --> l nu gamma) similar to 2.6 x 10(-5). The importance of these reactions in clarifying the dynamics of the annihilation graph is emphasized.