Subleading Shape Functions and the Determination of |V_{ub}|

Abstract

It is argued that the dominant subleading shape-function contributions to the endpoint region of the charged-lepton energy spectrum in B -> X_u l nu decays can be related in a model-independent way to an integral over the B -> X_s gamma photon spectrum. The square root of the fraction of B -> X_u l nu events with charged-lepton energy above E_0=2.2 GeV can be calculated with a residual theoretical uncertainty from subleading shape-function effects that it safely below the 10% level. These effects have therefore a minor impact on the determination of |V_{ub}|.