THE HETEROTIC LIFE OF THE D-PARTICLE

We study the dynamics of D-particles (D0-branes) in type I' string the ory and of the corresponding states in the dual heterotic description. We account for the presence of the two eight-orientifolds (eight-dime nsional orientifold planes) and sixteen D8-branes by deriving the appr opriate quantum mechanical system. We recover the familiar condition o f eight D8-branes for each eight-orientifold. We investigate bound sta tes and compute the phase shifts for the scattering of such states and find that they agree with the expectations from the supergravity acti on. In the type I' regime we study the motion transverse to the eight- orientifold and find an interesting cancellation effect.