A CLOSER LOOK AT PERTURBATIVE CORRECTIONS IN THE B-]C SEMILEPTONIC TRANSITIONS

We comment on two recent calculations of the second order perturbative corrections in the heavy flavor semileptonic transitions within the B rodsky-Lepage-Mackenzie approach. It is pointed out that the results d o not show significant enhancement either in the inclusive b --> c dec ays or in the exclusive amplitudes at zero recoil provided that the ex pansion parameter is chosen in a way appropriate to the kinematics at hand. The values of the second order coefficients inferred from the BL M type calculations appear to be of order unity in both cases. Thus, i n both cases no significant uncertainty in extracting V-cb can be attr ibuted to perturbative effects. The theoretical accuracy is mostly det ermined by the existing uncertainty in 1/m(c)(2) nonperturbative corre ctions in the exclusive B --> D- amplitude, and, to a lesser extent, by the uncertainty in the estimated value of the kinetic energy matrix element mu(pi)(2) in the case of Gamma(sl)(b --> c). The theoretical accuracy of the inclusive method of determining V-cb seemingly compete s with and even exceeds the experimental accuracy.