We revisit QCD sum rules for the decay constants of heavy-light mesons. In the sum rules for the vector mesons B * (s) and D * (s) we improve the accuracy of OPE, taking into account the O(α 2 s ) terms in the perturbative part and calculating the O(α s ) corrections to the quark-condensate contribution. With this accuracy, we obtain the ratios of decay constants: f B * /f B = 1.02 In order to assess the sensitivity of our calculation to the form of the sum rule, we consider alternative versions such as the power moments and Borel sum rules with different weights of the spectral density. We also investigated the heavy quark limit of the sum rules for vector and pseudoscalar mesons, estimating the violations of the heavy-quark spin and flavour symmetry.

Within the heavy quark expansion techniques for the heavy hadron weak decays we analytically compute the coefficient of the power suppressed dimension five chromo-magnetic operator at next-to-leading order of QCD perturbation theory with the full dependence on the final state quark mass. We present explicit expressions for the total width of inclusive semileptonic decays including the power suppressed terms and for a few moments of decay differential distributions.One of the important phenomenological applications of our results is precision analysis of the decays of bottom mesons to charmed final states and extraction of the numerical value for the CKM matrix entry |V cb |.

We present the results of a calculation of the perturbative QCD corrections for the semileptonic inclusive width of a heavy flavored meson. Within the Heavy Quark Expansion we analytically compute the QCD correction to the coefficient of power-suppressed contribution of chromo-magnetic operator in the limit of vanishing mass of the final state quark. The important phenomenological applications are decays of bottom mesons, and to the lesser extent, charmed mesons.