Exclusive semileptonic decays of B mesons into light mesons in the relativistic quark model

The exclusive semileptonic B → π(ϱ)eν decays are studied in the framework of the relativistic quark model based on the quasipotential approach in quantum field theory. The large recoil momentum of the final π(ϱ) meson allows for the expansion of the decay form factors at q2 = 0 in the inverse powers of b-quark mass. This considerably simplifies the analysis of these decays. The 1mb expansion is carried out up to the first order. It is found that the q2-dependence of the axial form factor A1 is different from the q2-behaviour of other form factors. We find Γ(B → πeν) = (3.1 ± 0.6) × |Vub|2 × 1012 s−1 and Γ(B → ϱeν) = (5.7 ± 1.2) × |Vub|2 × 1012 s−1. The relation between semileptonic and rare radiative B-decays is discussed.