Colliding string waves and duality

The collision of plane waves corresponding to massless states of closed str ing is considered in D-dimensional space-time. The reduced tree level effec tive action is known to be manifestly O (d, d) invariant, d being the numbe r of transverse spatial dimensions in the collision process. We adopt a cos et space reformulation of the effective two-dimensional theory and discuss the relation of this process with classical integrable systems in two dimen sions in the presence of gravity. We show how it is possible to generate ne w backgrounds for the scattering process, from known background solutions t o the equations of motion, in the coset reformulation. We present explicit calculations for the case of four space-time dimensions as an illustrative example. (C) 2001 Elsevier Science BN. All rights reserved.