Planckian Scattering and Black Holes
  Recently, 't Hooft's S-matrix for black hole evaporation, obtained from the gravitational interactions between the in-falling particles and Hawking radiation, has been generalised to include transverse effects. The action describing the collision turned out to be a string theory action with an antisymmetric tensor background. In this article we show that the model reproduces both the correct longitudinal and transverse dynamics, even when one goes beyond the eikonal approximation or particles collide at nonvanishing incidence angles. It also gives the correct momentum tranfer that takes place in the process. Including a curvature on the horizon provides the action with an extra term, which can be interpreted as a dilaton contribution. The amplitude of the scattering is seen to reproduce the Veneziano amplitude in a certain limit, as in earlier work by 't Hooft. The theory resembles a "holographic" field theory, in the sense that it only depends on the horizon degrees of freedom, and the in- and out-Hilbert spaces are the same. The operators representing the coordinates of in- and out-going particles are non-commuting, and Heisenberg's uncertainty principle must be corrected by a term proportional to the ratio of the ingoing momentum to the impact parameter, times Newton's constant. Reducing to 2+1 dimensions, we find that the coordinates satisfy an SO(2,1) algebra. 
Sebastian de Haro (Utrecht University)