Radiative Leptonic Decays of the charged $B$ and $D$ Mesons Including   Long-Distance Contribution
  In this work we study the radiative leptonic decays of $B^-$, $D^-$ and $D_s^-\to \gamma l \bar{\nu}$, including both the short-distance and long-distance contributions. The short-distance contribution is calculated by using the relativistic quark model, where the bound state wave function we used is that obtained in the relativistic potential model. The long-distance contribution is estimated by using vector meson dominance model. 
Ji-Chong Yang and Mao-Zhi Yang
hep-ph