Taming the end-point singularities in heavy-to-light decays

Abstract

It is argued that there is a fundamental momentum cutoff in heavy-to-light transitions, which is caused by possible Cherenkov gluon radiation when an energetic light parton travels through the ''brown muck''. The soft-overlap contributions where the partonic momenta configuration is highly asymmetric are disfavored, and the problematic end-point singularities and the double countings are absent in this framework. A simple calculation with a natural scale for the cutoff gives a plausible result for the $B\to \pi$ form factor.

Comments: 7 pages, 1 figure. Typos corrected; to appear in Phys. Rev. D (Rap. Comm.)