Probing bound states of D-branes

A zero-brane is used to probe non-threshold BPS bound states of (p, p + 2, p + 4)-branes. At long distances the string calculations agree with the supergravity calculations. The supergravity description is given, using the interpretation of the D = 8 dyonic membrane as the bound state of a two-brane inside a four-brane. We investigate the short distance structure of these bound states, compute the phase shift of the scattered zero-brane and find the bound states' characteristic size. It is found that there should be a supersymmetric solution of type IIa supergravity, describing a bound state of a zero-brane and two orthogonal two-branes, all inside a four-brane, with an additional unbound zero-brane. We comment on the relationship between p-branes and (p - 2)-branes.