COMMENT ON THE RENORMALIZATION GROUP IMPROVEMENT IN EXCLUSIVE b→c TRANSITIONS
Nikolai Uraltsev · Modern Physics Letters A · 1995
We argue, using rather general considerations, that the corrections to the exact one-loop expressions for the perturbative factors ηA, ηV in the exclusive zero recoil semileptonic transitions, inferred from the existing next-to-leading logarithmic summations of terms log mb/mc, are numerically irrelevant for actual values of mc and mb. Adopting these corrections for the values of the form factors is misleading. Likewise one cannot estimate their theoretical uncertainty in this way. The central theoretical value for ηA if taken literally is then ηA≃0.965.