String Theory and Classical Absorption by Threebranes

TL;DR

This paper compares string theory and classical gravity calculations of particle absorption by threebranes, extending previous results and exploring the agreement for various particles and brane configurations, revealing both consistencies and gaps in understanding.

Contribution

It extends the analysis of absorption cross-sections to Ramond-Ramond scalars and gravitons, and compares string theory results with classical gravity for threebranes, highlighting areas needing further research.

Findings

Precise agreement for dilaton absorption cross-section.

Extension to Ramond-Ramond scalars and gravitons.

Discrepancies in M-theory two- and fivebranes coefficients.

Abstract

Low energy absorption cross-sections for various particles falling into extreme non-dilatonic branes are calculated using string theory and world-volume field theory methods. The results are compared with classical absorption by the corresponding gravitational backgrounds. For the self-dual threebrane, earlier work by one of us demonstrated precise agreement of the absorption cross-sections for the dilaton, and here we extend the result to Ramond-Ramond scalars and to gravitons polarized parallel to the brane. In string theory, the only absorption channel available to dilatons and Ramond-Ramond scalars at leading order is conversion into a pair of gauge bosons on the threebrane. For gravitons polarized parallel to the brane, scalars, fermions and gauge bosons all make leading order contributions to the cross-section, which remarkably add up to the value predicted by classical gravity. For the twobrane and fivebrane of M-theory, numerical coefficients fail to agree, signalling 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 brane. We also consider the generalization to higher partial waves of minimally coupled scalars. We demonstrate agreement for the threebrane at l=1 and indicate that further work is necessary to understand l>1.