NLO deflections for spinning particles and Kerr black holes

TL;DR

This paper calculates classical momentum deflections of spinning particles in electrodynamics and gravity up to one loop, extending results to all spins in certain limits and employing unitarity and Feynman diagram methods.

Contribution

It introduces a comprehensive method to compute NLO momentum deflections for spinning bodies in electrodynamics and gravity, including all spin orders in the probe limit.

Findings

Results valid for all spins at tree level.

Extension to all spin orders in the heavy source at NLO.

Employs both unitarity and Feynman diagram approaches.

Abstract

We employ the "KMOC" formalism of [1] to compute classical momentum deflections of spinning bodies with arbitrary spin orientations up to next-to-leading order (one loop). We do this in electrodynamics and gravity. The final result, valid for generic masses, is true for all spins at tree level and up to second (fourth) spin order for the electromagnetic (gravity) case at one loop. Furthermore, emphasis is given to the probe limit scenario where our results extend to all spin orders in the heavy source, even at next-to-leading order. We carry out our computations both using a unitarity based framework and Feynman diagrammatic approach which relies on scattering amplitudes computed on fixed backgrounds.