Light-like Scattering in Quantum Gravity

TL;DR

This paper uses modern amplitude techniques within quantum gravity as an effective field theory to analyze light-like scattering, confirming classical predictions like light bending and exploring quantum effects.

Contribution

It introduces a simplified method for calculating gravitational scattering of light-like particles using amplitude techniques and verifies classical results within a quantum framework.

Findings

Classical gravitational effects are universal across matter types.

Confirmed the post-Newtonian correction for light bending.

Discussed quantum effects via eikonal approximation.

Abstract

We consider scattering in quantum gravity and derive long-range classical and quantum contributions to the scattering of light-like bosons and fermions (spin-0, spin-1/2, spin-1) from an external massive scalar field, such as the Sun or a black hole. This is achieved by treating general relativity as an effective field theory and identifying the non-analytic pieces of the one-loop gravitational scattering amplitude. It is emphasized throughout the paper how modern amplitude techniques, involving spinor-helicity variables, unitarity, and squaring relations in gravity enable much simplified computations. We directly verify, as predicted by general relativity, that all classical effects in our computation are universal (in the context of matter type and statistics). Using an eikonal procedure we confirm the post-Newtonian general relativity correction for light-like bending around large stellar objects. We also comment on treating effects from quantum hbar dependent terms using the same eikonal method.