CLOSED STRING RADIATION FROM MOVING D-BRANES

We compute the amplitude for the radiation of massless NS-NS closed st ring states from the interaction of two moving D-branes. We consider p article-like D-branes with reference to four-dimensional spacetime, in toroidal and orbifold compactifications, and we calculate the relevan t world sheet propagators within the moving boundary state formalism. We find no on-shell axion emission. For large inter-brane separation, we compute the spacetime graviton emission amplitude and estimate the average energy radiated, whereas the spacetime dilaton amplitude is fo und to vanish in this limit. The possibility of emission of other mass less states depends on the nature of the branes and of the compactific ation scheme. (C) 1998 Elsevier Science B.V.