O(alpha_s^2) corrections to b -> c decay at zero recoil

Abstract

Analytic formulae are presented for the two-loop perturbative QCD corrections to b -> c decay at the zero recoil point, which are required for the extraction of |V_bc| from measurements of exclusive B -> D* l nu decays. The results are in agreement with those of Czarnecki and Melnikov. Some comments on the numerical evaluation of the diagrams involved are made.

Comments: Latex, 12 pages, 13 postscript figures included with epsfig