Theoretical Aspects of Semileptonic B decays

Abstract

Strong interactions are addressed in connection to extracting |V_{cb}| and determining heavy quark parameters. A comprehensive approach allows a robust analysis not relying on a 1/m_c expansion; a percent defendable accuracy in |V_{cb}| becomes realistic. Some of the heavy quark parameters are already accurately known. We have at least one nontrivial precision check of the OPE at the nonperturbative level in inclusive decays. The alleged controversy between theory and BaBar data on <M_X^2> is argued to be an artefact of oversimplifying the OPE for high cuts in lepton energy. Consequences of the proximity to the `BPS' limit are addressed and their accuracy qualified. It is suggested that theory-wise B->D l\nu near zero recoil offers an accurate way for measuring |V_{cb}|.