Interactions of type IIB D-branes from the D-instanton matrix model

We compute long-distance interaction potentials between certain 1/2 and 1/4 supersymmetric D-brane configurations of type IIB theory, demonstrating detailed agreement between classical supergravity and one-loop instanton matrix model results. This confirms the interpretation of D-branes as described by classical matrix model backgrounds as being 'populated' by a large number of D-instantons, i.e. as corresponding to non-marginal bound states of branes of lower dimensions. In the process, we establish a precise relation between matrix model expressions and non-abelian F4 terms in the super Yang-Mills effective action. (orig.)