Photon-photon scattering from a UV-complete gravity QFT

TL;DR

This paper investigates photon-photon scattering within a UV-complete quantum gravity framework, revealing how high-energy corrections relate to massive graviparticle exchanges and emphasizing unitarity without positivity.

Contribution

It provides a detailed analysis of photon-photon scattering in quadratic gravity, connecting low-energy amplitudes to UV physics and demonstrating the role of unitarity without positivity.

Findings

Tree-level cross section is well-behaved at all energies.

Effective forward scattering amplitude isolates graviton pole effects.

Unitarity without positivity influences scattering amplitude properties.

Abstract

Quantum quadratic gravity (QQG) produces a tree-level differential cross section for $\gamma\gamma\to\gamma\gamma$ that is well-behaved at all energies. From this we can study how the corrections to low energy scattering amplitudes are related to the UV physics, in particular to the exchange of the massive graviparticles. An effective forward scattering amplitude is obtained by separating out the effects of the $t$-channel graviton pole. This is possible due to the UV-completeness, and even though the Froissart bound is not satisfied. We then consider photon-photon scattering to two graviparticles and a further imaginary contribution to the $\gamma\gamma\to\gamma\gamma$ forward scattering amplitude. Unitarity without positivity is a key property of QQG and it impacts all our results.