# Bulk viscosity in 2D relativistic fluids: the effects of temperature and modifications to the Rayleigh-Brillouin spectrum

## TL;DR

This paper thoroughly analyzes how bulk viscosity in 2D relativistic fluids depends on temperature and relativistic effects, comparing detailed Boltzmann equation results with approximations, and discusses implications for the Rayleigh-Brillouin spectrum.

## Contribution

It provides a comprehensive analysis of bulk viscosity dependence on relativistic parameters in 2D fluids, including non-relativistic and ultra-relativistic limits, with comparisons to approximation methods.

## Key findings

- Bulk viscosity varies with the relativistic parameter z.
- Comparison between Boltzmann equation and relaxation time approximation results.
- Modifications to the Rayleigh-Brillouin spectrum due to bulk viscosity.

## Abstract

The dependence of the bulk viscosity with the relativistic parameter $z=kT/mc^{2}$, obtained through the complete Boltzmann equation [1,2], is thoroughly analyzed. A complete and rigorous examination of the relevant non-relativistic and ultra-relativistic limits is carried out in the case of a hard disk model and compared with the results obtained in the relaxation time approximation. The modifications of the non-vanishing bulk viscosity to the Rayleigh-Brillouin is briefly discussed.