STRING THEORY AND CLASSICAL ABSORPTION BY 3-BRANES

Low-energy absorption cross sections for various particles falling int o extreme non-dilatonic branes are calculated using string theory and world-volume field theory methods. The results are compared with class ical absorption by the corresponding gravitational backgrounds, For th e self-dual three-brane, earlier work by one of us demonstrated precis e agreement of the absorption cross sections for the dilaton, and here we extend the result to Ramond-Ramond scalars and to gravitons polari zed parallel to the brane. In string theory, the only absorption chann el available to dilatons and Ramond-Ramond scalars at leading order is conversion into a pair of gauge bosons on the three-brane. For gravit ons polarized parallel to the brane, scalars, fermions and gauge boson s all make leading-order contributions to the cross section, which rem arkably add up to the value predicted by classical gravity, For the tw o-brane and five-brane of M-theory, numerical coefficients fail to agr ee, signaling our lack of a precise understanding of the world-volume theory for large numbers of coincident branes. In many cases, we note a remarkable isotropy in the final state particle flux within the bran e. We also consider the generalization to higher partial waves of mini mally coupled scalars, We demonstrate agreement for the three-brane at l = 1 and indicate that further work is necessary to understand l > 1 . (C) 1997 Elsevier Science B.V.