Radiative corrections and semileptonic B decays

A prescription for approximating electroweak radiative corrections to weak decays is given. The method is illustrated for τ-->eνν¯ and a simplified (structureless) model of B-->Meν¯, M=D or π, where the complete O(α) corrections are known. Our procedure is shown to provide a proper description of radiation damping near the electron's end-point energy and a reasonable estimate of radiative corrections for much of the spectrum as well as the integrated rate. As a practical application, it is applied to the semileptonic decays B-->Xeν¯ where an exact O(α) treatment of radiative corrections is very difficult, but an estimate of their effect is important for the extraction of V_ub and leptonic branching ratios. We also discuss an 18% enhancement of Υ(4S)-->B⁺B^- relative to B⁰B¯ ⁰ due to large Coulomb corrections near threshold.