Bulk Viscosity of Quark-Gluon Plasma in Strong Magnetic Fields

TL;DR

This paper analyzes the bulk viscosity of quark-gluon plasma under strong magnetic fields, revealing unique quark-mass dependencies and the dominance of certain viscosity components, with implications for understanding plasma behavior in extreme conditions.

Contribution

It introduces a detailed calculation of the bulk viscosity in strong magnetic fields using the LLL approximation, highlighting the quark-mass dependence and the dominance of the parallel component.

Findings

Bulk viscosity along magnetic field is dominated by quarks in the LLL.

Quark contribution to bulk viscosity increases with magnetic field strength.

Shear viscosities are suppressed in strong magnetic fields.

Abstract

We investigate the viscosities of the quark-gluon plasma in strong magnetic fields within the leading-log and lowest Landau level (LLL) approximations. We first show that the bulk viscosity in the direction parallel to the magnetic field is the only component that has a contribution from the quarks occupying the LLL. We then compute the bulk viscosity from the Kubo formula and find an intriguing quark-mass dependence as a consequence of a competition between the suppression of the bulk viscosity by conformal symmetry and an enhancement of the mean-free path by chirality conservation, which governs the behavior in the massless limit. The quark contribution to the viscosity along the magnetic field becomes larger than the one in the absence of a magnetic field. We also briefly estimate the other transport coefficients by considering the contribution of gluons. We show that the shear viscosities are suppressed compared to their values in the absence of a magnetic field.