LIGHT-CONE SUPERSYMMETRY AND D-BRANES

D-brane boundary states for type II superstrings are constructed by en forcing the conditions that preserve half of the space-time supersymme try. A light-cone coordinate frame is used where time is identified as one of the coordinates transverse to the brane's (euclidean) world-vo lume so that the p-brane is treated as a (p + I)-instanton. The bounda ry states have the superspace interpretation of top or bottom states i n a light-cone string superfield. The presence of a non-trivial open-s tring boundary condensate give rise to the familiar D-brane source ter ms that determine the (linearized) Born-Infeld-like effective actions for p-branes and the (linearized) equations of motion for the massless fields implied by the usual p-brane ansatze. The 'energy' due to clos ed string exchange between separate D-branes is calculated (to lowest order in the string coupling) in situations with pairs of parallel, in tersecting as well as orthogonal branes - in which case the unbroken s upersymmetry may be reduced. Configurations of more than two branes ar e also considered in situations in which the supersymmetry is reduced to 1/8 or 1/16 of the full amount. The Ward identities resulting from the non-linearly realized broken space-time supersymmetry in the prese nce of a D-brane are also discussed.