LONG-DISTANCE INTERACTIONS OF D-BRANE BOUND-STATES AND LONGITUDINAL 5-BRANE IN M(ATRIX) THEORY

We discuss long-distance, low-velocity interaction potentials for proc esses involving a longitudinal M5-brane (corresponding in type IIA the ory language to the 1/4 supersymmetric bound state of a 4-brane and O- brane). We consider the following scattering configurations: (a) a D= 11 graviton off longitudinal M5-brane, or, equivalently, O-branes off marginal 4 parallel to 0 bound state; an (b) M2-brane off longitudinal M5-brane, or, equivalently, a nonmarginal 2+0 bound state off margina l 4 parallel to 0 bound state; (c) two parallel longitudinal M5-branes , or, equivalently, two 4 parallel to 0 marginal bound states. We demo nstrate the equivalence between the classical string theory (supergrav ity) and M(atrix) model (one-loop super Yang-Mills) results for the le ading terms in the interaction potentials. The supergravity results ar e obtained using a generalization of a classical probe method which al lows one to treat bound states of D-branes as probes by introducing no nzero world-volume gauge field backgrounds.