Physics – Condensed Matter – Statistical Mechanics
Scientific paper
2009-07-16
J. Stat. Mech. (2009) P07024
Physics
Condensed Matter
Statistical Mechanics
22 pages, 9 figures
Scientific paper
10.1088/1742-5468/2009/07/P07024
We discuss the well known Einstein and the Kubo Fluctuation Dissipation Relations (FDRs) in the wider framework of a generalized FDR for systems with a stationary probability distribution. A multi-variate linear Langevin model, which includes dynamics with memory, is used as a treatable example to show how the usual relations are recovered only in particular cases. This study brings to the fore the ambiguities of a check of the FDR done without knowing the significant degrees of freedom and their coupling. An analogous scenario emerges in the dynamics of diluted shaken granular media. There, the correlation between position and velocity of particles, due to spatial inhomogeneities, induces violation of usual FDRs. The search for the appropriate correlation function which could restore the FDR, can be more insightful than a definition of ``non-equilibrium'' or ``effective temperatures''.
Baldassarri Andrea
Puglisi Alfio
Villamaina Dario
Vulpiani Angelo
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