FINITE MASS CORRECTIONS TO LEPTONIC DECAY CONSTANTS IN THE HEAVY-QUARK EFFECTIVE THEORY

We calculate finite mass corrections to leptonic decay constants in HQET using QCD sum rules. The results are given to two-loop accuracy including renormalization group analysis. The contribution of unknown two-loop anomalous dimension matrix elements is estimated. We find that the 1/m(Q) corrections to f(P), the decay constant of a pseudoscalar meson, amount to -(23 +/- 4 +/- 2)% for the B meson. The first error comes from the sum rule uncertainty, the second one from unknown or not accurately known matrix elements in HQET. We obtain a ratio of vector to pseudoscalar decay constant of 1.00 +/- 0.07 + O(1/m(Q)2) for B mesons.