SU(3) Polyakov linear-sigma model: bulk and shear viscosity of QCD matter in finite magnetic field

TL;DR

This study investigates how strong magnetic fields influence the bulk and shear viscosities of QCD matter near the phase transition, using the SU(3) Polyakov linear-sigma model and comparing two computational approaches.

Contribution

It provides a detailed analysis of the temperature dependence of viscosities in magnetic fields, revealing the effects on phase transition dynamics and hydrodynamic stability.

Findings

Viscosities decrease rapidly near the critical temperature with increasing magnetic field.

A peak in viscosities appears at the critical temperature as magnetic field strength increases.

Magnetic fields accelerate the transition from hadron to quark-gluon plasma phases.

Abstract

Due to off-center relativistic motion of the charged spectators and the local momentum-imbalance of the participants, a short-lived huge magnetic field is likely generated, especially in relativistic heavy-ion collisions. In determining the temperature dependence of bulk and shear viscosities of the QCD matter in vanishing and finite magnetic field, we utilize mean field approximation to the SU($3$) Polyakov linear-sigma model (PLSM). We compare between the results from two different approaches; Green-Kubo correlation and Boltzmann master equation with Chapman-Enskog expansion. We find that both approaches have almost identical results, especially in the hadron phase. In the temperature dependence of bulk and shear viscosities relative to thermal entropy at the critical temperature, there is a rapid decrease in the chiral phase-transition and in the critical temperature with increasing magnetic field. As the magnetic field strength increases, a peak appears at the critical temperature ($T_c$). This can be understood from the small drop on the thermal entropy at $T_c$, which can be interpreted due to instability in the hydrodynamic flow of the quark-gluon plasma and soft statistical hadronization. It is obvious that, increasing magnetic field accelerates the transition from hadron to QGP phases (inverse catalysis), i.e., taking place at lower temperatures.