# Shear viscosity and electrical conductivity of relativistic fluid in presence of magnetic field: a massless case

## TL;DR

This paper derives expressions for shear viscosity and electrical conductivity of massless relativistic fluids in magnetic fields, using kinetic theory, and discusses implications for quark-gluon plasma and perfect fluid behavior.

## Contribution

It provides new sets of formulas for shear viscosity coefficients in magnetic fields, classified into parallel, perpendicular, and Hall components, extending previous tensor approaches.

## Key findings

- Derived 5 shear viscosity coefficients in magnetic fields.
- Found agreement with earlier results despite methodological differences.
- Discussed implications for quark-gluon plasma and perfect fluidity in heavy-ion collisions.

## Abstract

We have explored the shear viscosity and electrical conductivity calculations for bosonic and fermionic medium, which goes from without to with magnetic field picture and then their simplified massless expressions. In presence of magnetic field, 5 independent velocity gradient tensors can be designed, so their corresponding proportional coefficients, connected with the viscous stress tensor provide us 5 shear viscosity coefficients. In existing litterateurs, two sets of tensors are available. Starting from them, present work has obtained two sets of expressions for 5 shear viscosity coefficients, which can be ultimately classified into three basic components: parallel, perpendicular and Hall components as one get same for electrical conductivity at finite magnetic field. Our calculations are based on kinetic theory approach in relaxation time approximation. Repeating same mathematical steps for finite magnetic field picture, which traditionally practiced for without field case, we have obtained 2 sets of 5 shear viscosity components, whose final expressions are in well agreements with earlier references, although a difference in methodology or steps can be clearly noticed. Realizing the massless results of viscosity and conductivity for Maxwell-Boltzmann, Fermi-Dirac and Bose-Einstein distribution function, we have applied them for massless quark gluon plasma and hadronic matter phases, which can provide us a rough order of strength, within which actual results will vary during quark-hadron phase transition. Present work also indicates that magnetic field might have some role for building perfect fluid nature in RHIC or LHC matter. The lower bound expectation of shear viscosity to entropy density ratio is also discussed.