GRAVITATIONAL LENSING BY P-BRANES

The scattering of R-R gauge bosons off of Dirichlet p-branes is comput ed to leading order in the string coupling. The results are qualitativ ely similar to those found in the scattering of massless NS-NS bosons : ail p-branes with p greater than or equal to 0 exhibit stringy prope rties, in particular the Regge behavior. Both the R-R and NS-NS scatte ring amplitudes agree in the limit of small momentum transfer with sca ttering off the extremal R-R charged p-brane solutions found in the lo w-energy supergravities. We interpret this as evidence that Dirichlet- branes are an exact world-sheet description of the extremal p-branes. The -1-brane (D-instanton) is a special object which, unlike all other Dirichlet-branes, exhibits point-like behavior. We show that the fiel d theoretic scattering off of the R-R charged instanton solution to ty pe IIB supergravity exactly reproduces the full stringy calculation. A s an aside, we include a discussion of the entropy of nonextremal blac k holes in ten dimensions, produced by exciting the 0-brane.