Implementing nonlinear Compton scattering beyond the local constant field approximation

TL;DR

This paper critically examines the limitations of the local constant field approximation in modeling nonlinear Compton scattering and proposes an improved method for more accurate photon emission probability calculations in strong-field QED.

Contribution

It demonstrates the inadequacy of the LCFA for low-energy photon emissions and introduces a simple recipe to enhance numerical simulations beyond the LCFA approximation.

Findings

LCFA is insufficient for low-energy photon predictions

Proposed an improved emission probability expression

Enhances accuracy of strong-field QED simulations

Abstract

In the calculation of probabilities of physical processes occurring in a background classical field, the local constant field approximation (LCFA) relies on the possibility of neglecting the space-time variation of the external field within the region of formation of the process. This approximation is widely employed in strong-field QED as it allows to evaluate probabilities of processes occurring in arbitrary electromagnetic fields starting from the corresponding quantities computed in a constant electromagnetic field. Here, we demonstrate in the case of nonlinear single Compton scattering that the LCFA is quantitatively and qualitatively insufficient for describing the low-energy part of the emitted photon probability. In addition, we provide a simple recipe to implement an improved expression of the photon emission probability beyond the LCFA in numerical codes, which are an essential tool to interpret present and upcoming experiments in strong-field QED.