On Non-Perturbative Unitarity in Gravitational Scattering

We argue that the tree-level graviton-scalar scattering in the Regge limit is unitarized by non-perturbative effects within General Relativity. At Planckian energy the back reaction of the incoming graviton on the background geometry produces a non-perturbative plane wave which, in turn, softens the UV-behavior. Our amplitude then interpolates between the perturbative graviton-scalar scattering at low energy and scattering on a classical plane wave in the Regge limit.