A Model for High Energy Scattering in Quantum Gravity

TL;DR

The paper argues that high-energy scattering in quantum gravity, especially with large extra dimensions, can be largely described by semiclassical General Relativity above the Planck scale. It predicts a transition from perturbative, eikonal graviton exchange at large impact parameters to black hole production at small impact parameters, with the black holes decaying thermally via Hawking radiation and thereby suppressing elastic channels. The Schwarzschild radius rises with energy, expanding the regime where BH formation dominates, and the observed signals in low-scale gravity scenarios include jet suppression and Hawking radiation largely into invisible KK modes, complicating detection yet offering a distinctive signature. The analysis also discusses the regimes of weakly coupled string theory, indicating that a fully quantum gravitational treatment is required to connect perturbative string effects with the semiclassical BH description, depending on the compactification scales and the coupling.

Abstract

We present a model for high energy two body scattering in a quantum theory of gravity. The model is applicable for center of mass energies higher than the relevant Planck scale. At impact parameters smaller than the Schwarzchild radius appropriate to the center of mass energy and total charge of the initial state, the cross section is dominated by an inelastic process in which a single large black hole is formed. The black hole then decays by Hawking radiation. The elastic cross section is highly suppressed at these impact parameters because of the small phase space for thermal decay into a high energy two body state. For very large impact parameter the amplitude is dominated by eikonalized single graviton exchange. At intermediate impact parameters the scattering is more complicated, but since the Schwarzchild radius grows with energy, we speculate that a more sophisticated eikonal calculation which uses the nonlinear classical solutions of the field equations may provide a good approximation at all larger impact parameters. We discuss the extent to which black hole production will be observable in theories with low scale quantum gravity and large dimensions.