Two photon decays of heavy vector mesons B*→Bγγ, D*→Dγγ, and the possible determination of the g_B*(D*)B(D)π and g_B*0B0γ couplings

We study the novel decays B*→Bγγ and D*→Dγγ using the framework of the heavy meson chiral Lagrangian (HMχL) to leading order in chiral perturbation theory. The branching ratios of these decays are expressed in terms of the strong g_B*(D*)B(D)π and the electromagnetic g_B*(D*)B(D)γ couplings, thus providing a possible tool for their determination. In the charm case, using the experimentally determined ratios (D*^0,+ →Dπ)/(D*^0,+→Dγ), we are able to express the branching ratio as a function of the strong coupling only. We thus find 1.6x10^-6<Br(D*⁰→D ⁰γγ)<3.3x10^-5 for 0.25<g<1, where g is the strong coupling of HMχL. In the b-flavored sector, the Br(B*⁰→B⁰γγ) which we estimate to be in the 10^-7-10^-5 range is a function of both g_B*Bπ and g_B*Bγ. Its behavior does not afford an unambiguous determination of these couplings except for the region of high g values such as g>0.6. The expected two-photon differential distributions are presented for both B*⁰→B⁰γγ and D*⁰→γγ, for different values of the couplings involved.