Mass Effect on Axial Charge Dynamics

TL;DR

This paper investigates how finite quark mass influences axial charge dynamics using holographic models, revealing effects on generation, dissipation, and their dependence on magnetic fields and mass.

Contribution

It introduces a holographic approach to study the impact of quark mass on axial charge behavior, including diffusion rates and dissipation mechanisms.

Findings

Mass diffusion rate is non-monotonous with respect to quark mass.

Magnetic field enhances the helicity flipping rate significantly.

Mass term effectively dissipates axial charge over long times.

Abstract

We studied effect of finite quark mass on the dynamics of axial charge using the D3/D7 model in holography. The mass term in axial anomaly equation affects both the fluctuation (generation) and dissipation of axial charge. We studied the dependence of the effect on quark mass and external magnetic field. For axial charge generation, we calculated the mass diffusion rate, which characterizes the helicity flipping rate. The rate is a non-monotonous function of mass and can be significantly enhanced by the magnetic field. The diffusive behavior is also related to a divergent susceptibility of axial charge. For axial charge dissipation, we found that in the long time limit, the mass term dissipates all the charge effectively generated by parallel electric and magnetic fields. The result is consistent with a relaxation time approximation. The rate of dissipation through mass term is a monotonous increasing function of both quark mass and magnetic field.