Electromagnetic response in an expanding quark-gluon plasma

TL;DR

This paper investigates how the electromagnetic response of a quark-gluon plasma evolves during rapid expansion, revealing that temperature decrease suppresses and relaxation time increase enhances conductivity, impacting magnetic flux trapping and chiral magnetic effect observation.

Contribution

It extends previous kinetic theory analysis of electromagnetic response to an expanding quark-gluon plasma, highlighting the competing effects of temperature and relaxation time.

Findings

Decreasing temperature suppresses conductivity.

Increasing relaxation time enhances electromagnetic response.

Expansion dynamics influence magnetic flux trapping.

Abstract

The validity of conventional Ohm's law is tested in the context of a rapidly evolving quark-gluon plasma produced in heavy-ion collisions. Here we discuss the electromagnetic response using an analytical solution in kinetic theory. As conjectured previously, after switching on an electric field in a nonexpanding plasma, the time-dependent current is given by $\mathbf{J}(t)=(1-e^{-t/\tau_0}) \sigma_{0} \mathbf{E}$, where $\tau_0$ is the transport relaxation time and $\sigma_{0}$ is the steady-state electrical conductivity. Such an incomplete electromagnetic response reduces the efficiency of the magnetic flux trapping in the quark-gluon plasma and may prevent the observation of the chiral magnetic effect. Here we extend the study to the case of a rapidly expanding plasma. We find that the decreasing temperature and the increasing transport relaxation time have opposite effects on the electromagnetic response. While the former suppresses the time-dependent conductivity, the latter enhances it.