Collisional Energy Loss and the Chiral Magnetic Effect*

Collisional energy loss of a fast particle in a medium is mostly due to the medium polarization by the electromagnetic fields of the particle. In addition to Cherenkov radiation, in a chiral medium there is a contribution to the energy loss mostly in the form of chiral Cherenkov radiation due to induction of the anomalous current proportional to the magnetic field. We employ classical electrodynamics 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 Weyl semimetals, the 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 nonchiral medium is a slow, at most logarithmic, function of energy ɛ, the chiral Cherenkov radiation is proportional to ɛ^2 when the recoil is neglected and to ɛ when it is taken into account.