Fluctuations of internal energy flow in a vibrated granular gas

TL;DR

This paper investigates the non-equilibrium fluctuations of power flux in vibrated granular gases, clarifies the nature of the effective temperature, and discusses the limitations of the Fluctuation Relation in such systems.

Contribution

It introduces a two-temperature Poisson process model supported by simulations to explain experimental results and clarifies the role of effective temperature in granular gases.

Findings

Power flux fluctuations do not satisfy the Fluctuation Relation.

The effective temperature is explained as a two-temperature Poisson process.

Other global quantities may be needed to fulfill the Fluctuation Relation.

Abstract

The non-equilibrium fluctuations of power flux in a fluidized granular media have been recently measured in an experiment [Phys. Rev. Lett. 92, 164301, 2004], which was announced to be a verification of the Fluctuation Relation (FR) by Gallavotti and Cohen. An effective temperature was also identified and proposed to be a useful probe for such non equilibrium systems. We explain these results in terms of a two temperature Poisson process. Within this model, supported by independent Molecular Dynamics simulations, power flux fluctuations do not satisfy the FR and the nature of the effective temperature is clarified. In the pursue of a hypothetical global quantity fulfilling the FR, this points to the need of considering other candidates than the power flux.