New infra-red enhancements in 4-derivative gravity

TL;DR

This paper investigates 4-derivative gravity, revealing a new infrared enhancement called 'ghostrahlung' and showing how high-energy scatterings are moderated by radiation of weakly coupled gravitons and ghosts.

Contribution

It introduces the concept of 'ghostrahlung' and analyzes its effects on matter scattering in 4-derivative gravity, providing new insights into its infrared behavior.

Findings

Discovery of 'ghostrahlung' infrared enhancement.

High-energy scatterings are reduced to Planck scale by radiation.

Weakly coupled ghosts and gravitons carry away energy.

Abstract

4-derivative gravity provides a renormalizable theory of quantum gravity at the price of introducing a physical ghost, which could admit a sensible positive-energy quantization. To understand its physics, we compute ghost-mediated scatterings among matter particles at tree-level, finding a new power-like infra-red enhancement typical of 4-derivative theories, that we dub '$ghostrahlung$'. Super-Planckian scatterings get downgraded to Planckian by radiating hard gravitons and ghosts, which are weakly coupled and carry away the energy.