Polarized QED cascades

TL;DR

This paper investigates how including spin and polarization effects in strong-field QED processes alters cascade growth rates and particle polarization, revealing new phenomena like spin-straggling and potential for controlled experiments.

Contribution

It introduces a kinetic equation approach incorporating spin and polarization in QED cascades, highlighting the impact on growth rates and particle spectra in ultra-intense laser fields.

Findings

Growth rate of QED cascades can be reduced by polarization effects.

Particles produced are highly polarized, with spectra showing spin-dependent features.

Photon polarization influences early-stage particle production, enabling experimental control.

Abstract

By taking the spin and polarization of the electrons, positrons and photons into account in the strong-field QED processes of nonlinear Compton emission and pair production, we find that the growth rate of QED cascades in ultra-intense laser fields can be substantially reduced. While this means that fewer particles are produced, we also found them to be highly polarized. We further find that the high-energy tail of the particle spectra is polarized opposite to that expected from Sokolov-Ternov theory, which cannot be explained by just taking into account spin-asymmetries in the pair production process, but results significantly from "spin-straggling". We employ a kinetic equation approach for the electron, positron and photon distributions, each of them spin/polarization-resolved, with the QED effects of photon emission and pair production modelled by a spin/polarization dependent Boltzmann-type collision operator. For photon-seeded cascades, depending on the photon polarization, we find an excess or a shortage of particle production in the early stages of cascade development, which provides a path towards a controlled experiment. Throughout this paper we focus on rotating electric field configuration, which represent an idealized model and allows for a straightforward interpretation of the observed effects.