FINAL-STATE RESCATTERING AS A CONTRIBUTION TO B-]RHO-GAMMA

We provide a new estimate of the long-distance component to the radiat ive transition B-->rho gamma. Our mechanism involves the soft scatteri ng of on-shell hadronic products of nonleptonic B decay, as in the cha in B-->rho rho-->rho gamma. We employ a phenomenological fit to scatte ring data to estimate the effect. The specific intermediate states con sidered here modify the B-->rho gamma decay rate at roughly the 5-8% l evel, although the underlying effect has the potential to be larger. C ontrary to other mechanisms of long distance physics which have been d iscussed in the literature, this yields a non-negligible modification of the B-0-->rho(0) gamma channel and hence will provide an uncertaint y in the extraction of V-td. This mechanism also affects the isospin r elation between the rates for B--->rho(-)gamma and B-0-->rho(0) gamma and may generate CP asymmetries at experimentally observable levels.