COMPOSITE BPS CONFIGURATIONS OF P-BRANES IN 10 AND 11 DIMENSIONS

We give an overview of various composite BPS configurations of string theory and M-theory p-branes represented as classical supergravity sol utions. Type II string backgrounds can be obtained by S-and T-dualitie s from the NS-NS configurations corresponding to exact conformal sigma -models. The single-centre solutions can also be generated from the Sc hwarzschild solution by applying a sequence of boosts, 'smearings' in some number of dimensions, dualities and taking the extremal limit. Th e basic 'marginal' backgrounds representing threshold BPS bound states of branes are parametrized by a number of independent harmonic functi ons, one for each brane. 'Non-marginal' BPS configurations in D = 10 c an be constructed from the marginal ones using U-duality and thus are parametrized, in addition to harmonic functions, by a finite number of O(d, d) and SL(2, R) 'angles'. Some of them can be viewed as dimensio nal reductions of coordinate-transformed (boosted or rotated) marginal configurations of M-branes. We present a new more general class of co nfigurations in which some of the branes or their intersection spaces are localized on other branes. In particular, we find the supergravity background describing the type II BPS configuration of a 3-brane, RR 5-brane and NS-NS 5-brane, and a related 'localized' 2-5-5 D = 11 solu tion. We also consider the classical action for a 3-brane probe moving in such type IIB backgrounds and determine the structure of the corre sponding moduli space metrics.