Eikonal Approach to Planck Scale Physics

We consider gravitational scattering of point particles with Planckian centre-of-mass energy and fixed low momentum transfers in the framework of general relativity and dilaton gravity. The geometry around the particles are modelled by arbitrary black hole metrics of general relativity to calculate the scattering amplitudes. However, for dilaton gravity, this modelling can be done {\it only} by extremal black hole metrics. This is consistent with the conjecture that extremal black holes are elementary particles.