Quantum string scattering by gravitational shock waves

Abstract

The two-point amplitude, A 2( k 2, k 1), describing the scattering of the lowest string excitation (the tachyon) by a gravitational shock wave (GSW) is computed. For this purpose, we use the appropriate vertex operator in the GSW background. We explicitly evaluate A 2( k 2, k 1) for large impact parameters q. It is given by the Coulombian amplitude plus string corrections of order s q ( s = ( k 1 + k 2) 2), for large q. These string corrections produce an infinite sequence of imaginary poles in s, the semi-infinite sequence of Coulomb poles noticed by 't Hooft always remaining present.