High energy scattering in gravity and supergravity

TL;DR

This paper explores high-energy scattering in gravity and supergravity, emphasizing the dominance of long-distance physics, the limitations of short-distance approaches, and the need for a nonperturbative unitarity-preserving theory.

Contribution

It demonstrates that long-range dynamics govern ultraplanckian scattering and highlights the challenges in probing asymptotic safety and unitarity within perturbative frameworks.

Findings

Gravity and supergravity amplitudes share similar long-distance behavior.

Short-distance divergences do not dominate in high-energy scattering.

Perturbative amplitudes remain finite, but unitarity issues persist.

Abstract

We investigate features of perturbative gravity and supergravity by studying scattering in the ultraplanckian limit, and sharpen arguments that the dynamics is governed by long-distance physics. A simple example capturing aspects of the eikonal resummation suggests why short distance phenomena and in particular divergences or nonrenormalizability do not necessarily play a central role in this regime. A more profound problem is apparently unitarity. These considerations can be illustrated by showing that known gravity and supergravity amplitudes have the same long-distance behavior, despite the extra light states of supergravity, and this serves as an important check on long-range dynamics in a context where perturbative amplitudes are finite. We also argue that these considerations have other important implications: they obstruct probing the conjectured phenomenon of asymptotic safety through a physical scattering process, and ultraplanckian scattering exhibiting Regge behavior. These arguments sharpen the need to find a nonperturbative completion of gravity with mechanisms which restore unitarity in the strong gravity regime.