Validity of Gallavotti-Cohen Fluctuation Relation in driven granular gases

ABSTRACT: In a recent experiment it has been claimed that the Gallavotti and Cohen’s Fluctuation Relation (FR) is satisied by the fluctuations of power injection in a vibrated granular gas. Anyway, by simple reasoning, it can be shown that for a granular gas such a relation cannot be true. We have studied numerically and analytically the fluctuations of power injection in different models. FR never holds. In the case of boundary driving it can be calculated the behavior at intermediate, observable times, of internal power injection, obtaining quantitative agreement with the experiment. In the case of homogeneous driving a general theory can be obtained, predicting the behavior of the large deviation function of the fluctuations of power injected by the thermostat. Finally we suggest a possible route to define an entropy production, measurable in granular gases, which must satisfy the FT.