String scattering from D-branes in type 0 theories

We derive fully covariant expressions for all two-point scattering amplitud es involving a closed string tachyon and massless strings from the Dirichle t brane in type 0 theories. The amplitude for two massless D-brane fluctuat ions to produce a closed string tachyon is also evaluated. We then examine in detail these string scattering amplitudes in order to extract world-volu me couplings of the tachyon with itself and with massless fields on a D-bra ne. We find that the tachyon appears as an overall coupling function in the Born-Infeld action and conjecture the form of the function. (C) 1999 Publi shed by Elsevier Science B.V. All rights reserved.