On-shell approach to (spinning) gravitational absorption processes

TL;DR

This paper develops a novel on-shell amplitude approach to model spinning gravitational absorption, connecting it to spheroidal harmonics and fixing coefficients via known cross-sections, with applications to gravitational Compton amplitudes.

Contribution

It introduces a new on-shell framework for gravitational absorption involving spinning particles, linking it to spheroidal harmonics and providing a method to determine Wilson coefficients from cross-section data.

Findings

Representation of spheroidal harmonics via on-shell amplitudes

Fixing Wilson coefficients using known absorption cross-sections

Calculation of absorption-induced corrections to gravitational Compton amplitudes

Abstract

We utilize three point amplitudes with (spinning) particles of unequal mass and a graviton to capture the dynamics of absorption processes. We demonstrate that the construction can represent the spheroidal harmonics appearing in the Teukolsky equations. The absolute square of the ``Wilson coefficients'' in this effective description can be fixed by matching to the known absorptive cross-sections. As an application, we compute corrections to the gravitational Compton amplitude from the exchange of states corresponding to such absorption effects. In the super-extremal limit, the corrections generate the non-analytic $|a|$-dependent contribution of the Compton amplitude found in ref.\cite{Bautista:2022wjf}.