Radiative leptonic decays of heavy mesons in heavy quark limit

We study the radiative leptonic decays of heavy mesons within the covariant light-front model. Using this model, both the form factors FV and FA have the same form when the heavy quark limit is taken. In addition, the relation between the form factor FV and the decay constant of a heavy meson FH is obtained. The hadronic parameter β can be determined by the parameters appearing in the wave function of the heavy meson. We find that the value of β is not only quite smaller than the one in the non-relativistic case, but also insensitive to the value of the light quark mass mq. These results mean that the relativistic effects are very important in this work. We also obtain that the branching ratio of B→lνlγ is about (1.40-1.67) x 10-6, in agreement with the general estimates in the literature. (orig.)