Breakdown of the fluctuation-dissipation relations in granular gasesJ. J. Brey1, M. I. García de Soria1, 2 and P. Maynar1, 3
1 Física Teórica, Universidad de Sevilla - Apartado de Correos 1065, E-41080 Sevilla, Spain, EU
2 LPTMS (CNRS UMR 8626), Université Paris-Sud - Orsay Cedex, F-91405 France, EU
3 Laboratoire de Physisque Théorique (CNRS UMR 8627), Bâtiment 210, Université Paris-Sud Orsay Cedex, F-91405 France, EU
received 13 June 2008; accepted in final form 3 September 2008; published October 2008
published online 6 October 2008
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 modeled as an ensemble of inelastic hard particles 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.
45.70.-n - Granular systems.
51.10.+y - Kinetic and transport theory of gases.
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