Superstring scattering from D-branes bound states

We derive fully covariant expressions for disk scattering amplitudes of any two massless closed strings in which mixed Neumann and Dirichlet world-she et boundary conditions are included. From the two-point amplitudes, we deri ve the long range background fields and verify that they correspond to Dp-b rane bound state. Also, from the scattering amplitudes, we calculate the li near coupling of closed string fields to D-brane world-volume and show that they are consistent with Born-Infeld and Chern-Simons actions in the prese nce of a background field.