Measuring chiral imbalance with collisional energy loss

TL;DR

This paper investigates how chiral imbalance in a plasma affects the collisional energy loss of a high-energy fermion, revealing a helicity-dependent contribution that could serve as a diagnostic tool.

Contribution

It introduces a novel helicity-dependent term in the energy loss calculation, linking chiral imbalance to measurable differences in fermion energy loss.

Findings

Helicity-dependent energy loss contributions can be comparable to leading-order results.

Hard photon or gluon exchange dominates the helicity-dependent effects.

Dimensional regularization effectively handles soft photon exchange contributions.

Abstract

We compute the collisional energy loss of an {energetic} massive fermion crossing a chiral plasma at finite temperature characterized by an imbalance between the populations of left-handed and right-handed fermions. We find a new contribution to the energy loss which is proportional to the helicity of the test fermion and depends on the amount of chiral imbalance in the plasma. We then compute the difference between the energy loss of a fermion with the two opposite helicities, to assess whether this could be used to quantify the chiral imbalance in the plasma. We find that the leading contribution to these helicity-dependent energy loss contributions comes from the exchange of hard photons (or gluons for QCD) with the medium constituents, and in some scenarios can become comparable to the leading-order result for a plasma without any chiral imbalance. We also evaluate the contribution arising from soft photon exchange, which is a subleading effect, and requires regularization. We illustrate how dimensional regularization is a well suited prescription to be applied to these energy loss computations.