# Radiation beaming in the quantum regime

## TL;DR

This paper investigates quantum radiation reaction effects, revealing that electrons can scatter out-of-plane due to finite photon emission angles, with Monte Carlo simulations aligning well with quantum electrodynamics predictions.

## Contribution

It introduces a Monte Carlo method for angularly resolved emission rates that improves agreement with QED calculations of nonlinear Compton scattering.

## Key findings

- Electron scattering out-of-plane due to quantum recoil
- Monte Carlo simulations match QED results
- Increased beam divergence observed in high-intensity interactions

## Abstract

Classical theories of radiation reaction predict that the electron motion is confined to the plane defined by the electron's instantaneous momentum and the force exerted by the external electromagnetic field. However, in the quantum radiation reaction regime, where the recoil exerted by individual quanta becomes significant, the electron can scatter `out-of-plane', as the photon is emitted into a cone with finite opening angle. We show that Monte Carlo implementation of an angularly resolved emission rate leads to substantially improved agreement with exact QED calculations of nonlinear Compton scattering. Furthermore, we show that the transverse recoil caused by this finite beaming, while negligible in many high-intensity scenarios, can be identified in the increase in divergence, in the plane perpendicular to the polarization, of a high-energy electron beam that interacts with a linearly polarized, ultraintense laser.