Breakdown of fluctuation-dissipation relations in granular gases

TL;DR

This study uses molecular dynamics simulations to examine the fluctuation-dissipation relations in granular gases, revealing that while a Langevin approach is applicable, the relation requires modification due to differing viscosity parameters.

Contribution

It provides the first detailed numerical analysis of fluctuation-dissipation relations in granular gases, highlighting the need to modify traditional Langevin models.

Findings

Langevin approach can describe granular gas fluctuations.

The viscosity parameter in fluctuation-dissipation relations differs from shear viscosity.

Modification of fluctuation-dissipation relation is necessary for granular gases.

Abstract

A numerical molecular dynamics experiment measuring the two-time correlation function of the transversal velocity field in the homogeneous cooling state of a granular gas is reported. By measuring the decay rate and the amplitude of the correlations, the accuracy of the Landau-Langevin equation of fluctuating hydrodynamics is checked. The results indicate that although a Langevin approach can be valid, the fluctuation-dissipation relation must be modified, since the viscosity parameter appearing in it differs from the usual hydrodynamic shear viscosity.