Collisional energy loss and the Chiral Magnetic Effect

TL;DR

This paper investigates how chiral media influence the energy loss of fast particles, revealing a significant enhancement due to chiral Cherenkov radiation, with potential experimental implications in quark-gluon plasma and Weyl semimetals.

Contribution

It introduces a classical electrodynamics approach to quantify collisional energy loss in chiral media, highlighting the role of chiral Cherenkov radiation and its energy dependence.

Findings

Chiral Cherenkov radiation causes energy loss to scale with E^2 (neglecting recoil) and E (including recoil).

Photon spectrum is enhanced in ultraviolet and X-ray regions in Weyl semimetals.

Energy loss in non-chiral media is a slow, logarithmic function of energy.

Abstract

Collisional energy loss of a fast particle in a medium is mostly due to the medium polarization by the electromagnetic fields of the particle. A small fraction of energy is carried away by the Cherenkov radiation. In chiral medium there is an additional contribution to the energy loss due to induction of the anomalous current proportional to the magnetic field. It causes the particle to lose energy mostly in the form of the \emph{chiral} Cherenkov radiation. We employ classical electrodynamics, adequate in a wide range of particle energies, to compute the collisional energy loss by a fast particle in a homogenous chiral plasma and apply the results to Quark-Gluon Plasma and a Weyl semimetal. In the later case photon spectrum is strongly enhanced in the ultraviolet and X-ray regions which makes it amenable to experimental investigation. Our main observation is that while the collisional energy loss in a non-chiral medium is a slow, at most logarithmic, function of energy $E$, the chiral Cherenkov radiation is proportional to $E^2$ when the recoil is neglected and to $E$ when it is taken into account.