Renormalon Analysis of Heavy-Light Exclusive B Decays

We study two-body exclusive decays of the form B -> D^(*) L (L = \pi, \rho) in the heavy quark limit. We perform a renormalon analysis of such processes to determine the order at which nonperturbative factorization-breaking power corrections enter the amplitude. We find that a class of leading power corrections to the color octet matrix element, of O(\Lambda_QCD/m_b), vanish in the limit of a symmetric light meson parton distribution function. We discuss the phenomenological significance of this result.