Magnetohydrodynamics of Chiral Relativistic Fluids

TL;DR

This paper develops a magnetohydrodynamical framework for high-temperature relativistic plasmas of charged fermions, incorporating a chiral pseudo-scalar field that influences magnetic field evolution and introduces new dynamical phenomena.

Contribution

It introduces a novel MHD model including a chiral pseudo-scalar field, derived from fermion density asymmetries, affecting plasma dynamics and magnetic field behavior.

Findings

The model includes a chiral pseudo-scalar field coupled to magnetic fields.

The axion-like field impacts plasma evolution and induces inverse cascade phenomena.

New dynamical equations account for chiral anomaly effects in relativistic MHD.

Abstract

We study the dynamics of a plasma of charged relativistic fermions at very high temperature $T\gg m$, where $m$ is the fermion mass, coupled to the electromagnetic field. In particular, we derive a magneto-hydrodynamical description of the evolution of such a plasma. We show that, as compared to conventional MHD for a plasma of non-relativistic particles, the hydrodynamical description of the relativistic plasma involves new degrees of freedom described by a pseudo-scalar field originating in a local asymmetry in the densities of left-handed and right-handed fermions. This field can be interpreted as an effective axion field. Taking into account the chiral anomaly we present dynamical equations for the evolution of this field, as well as of other fields appearing in the MHD description of the plasma. Due to its non-linear coupling to helical magnetic fields, the axion field significantly affects the dynamics of a magnetized plasma and can give rise to a novel type of inverse cascade.