The baffling semileptonic branching ratio of B mesons

Abstract

The apparent gap between the measured and the expected value for the semileptonic branching ratio of B mesons has become more serious of r the last year. This is due to the improved quality of the data and to the increasing maturity of the theoretical treatment of nonperturbative corrections. We discuss various theoretical options to reduce the semileptonic B branching ratio; among the more spectacular resolutions of the apparent puzzle is the possibility of an unorthodox enhancement in nonperturbative corrections or even of an intervention by “New Physics”. Phenomenological implications of such scenarios are pointed out.