Angular momentum of the asymptotic electromagnetic field in the classical scattering of charged particles

TL;DR

This paper calculates the angular momentum of electromagnetic fields during charged particle scattering, revealing a time-independent shift linked to electromagnetic memory effects and emphasizing its importance in quantum infrared divergence contexts.

Contribution

It introduces a method to compute the electromagnetic angular momentum in scattering events and highlights its significance for understanding asymptotic states in quantum theories.

Findings

Discovered a time-independent angular momentum contribution in electromagnetic scattering.

Linked the angular momentum shift to a potential electromagnetic memory effect.

Showed the necessity of including this angular momentum in quantum infrared divergence analyses.

Abstract

We compute the angular momentum of the electromagnetic field on a late time Cauchy surface with an arbitrary constant normal vector relevant for the classical scattering of charged particles. We find a time independent contribution to the angular momentum. This demonstrates that every charged particle scattering event is accompanied by a net shift in the angular momentum of the electromagnetic field. We speculate that this shift is related to a subleading electromagnetic memory effect. We argue that this asymptotic angular momentum should be included in the description of the asymptotic states in quantum theories containing infrared divergences. We demonstrate that the Lorentz covariance of the asymptotic electromagnetic angular momentum can only be exhibited upon making reference to the Cauchy slice's normal vector.