Towards an S-matrix description of gravitational collapse

Abstract

Extending our previous results on trans-Planckian (Gs >> ) scattering of light particles in quantum string-gravity we present a calculation of the corresponding S-matrix from the region of large impact parameters (\ls$">b >> G(s) 1/2>λ s) down to the regime where classical gravitational collapse is expected to occur. By solving the semiclassical equations of a previously introduced effective-action approximation, we find that the perturbative expansion around the leading eikonal result diverges at a critical value b = b c = O(G(s) 1/2), signalling the onset of a new (black-hole related?) regime. We then discuss the main features of our explicitly unitary S-matrix - and of the associated effective metric - down to (and in the vicinity of) b = b c, and present some ideas and results on its extension all the way to the b0 region. We find that for b