Absorptive Effects and Classical Black Hole Scattering

TL;DR

This paper introduces a model-independent method to incorporate black hole horizon absorption effects into scattering amplitude calculations, aligning with previous results and offering an alternative approach to the gravitational two-body problem.

Contribution

It develops an on-shell scattering amplitudes framework to include horizon absorption effects in black hole scattering, using an effective coupling to internal degrees-of-freedom.

Findings

Agreement with previous worldline Schwinger-Keldysh calculations

Provides a new on-shell approach to horizon absorption effects

Calculates leading absorptive contributions to black hole scattering

Abstract

We describe an approach to incorporating the physical effects of the absorption of energy by the event horizon of black holes in the scattering amplitudes based post-Minkowskian, point-particle effective description. Absorptive dynamics are incorporated in a model-independent way by coupling the usual point-particle description to an invisible sector of gapless internal degrees-of-freedom. The leading order dynamics of this sector are encoded in the low-energy expansion of a spectral density function obtained by matching an absorption cross section in the ultraviolet description. This information is then recycled using the scattering amplitudes based Kosower-Maybee-O'Connell in-in formalism to calculate the leading absorptive contribution to the impulse and change in rest mass of a Schwarzschild black hole scattering with a second compact body sourcing a massless scalar, electromagnetic or gravitational field. The results obtained are in complete agreement with previous worldline Schwinger-Keldysh calculations and provide an alternative on-shell scattering amplitudes approach to incorporating horizon absorption effects in the gravitational two-body problem.