Irreversible dynamics of a massive intruder in dense granular fluids

TL;DR

This paper introduces a generalized Langevin equation with memory effects to model the dynamics of a large intruder in dense granular fluids, revealing violations of equilibrium fluctuation-dissipation relations and confirming fluctuation relations through entropy production measurements.

Contribution

It proposes a novel Langevin model with exponential memory for dense granular fluids and identifies the source of memory as coupling between tracer velocity and local fluid velocity.

Findings

Model reproduces numerical correlation and response functions.

Violates equilibrium Fluctuation Dissipation relations.

Verifies Fluctuation Relation through entropy production measurement.

Abstract

A Generalized Langevin Equation with exponential memory is proposed for the dynamics of a massive intruder in a dense granular fluid. The model reproduces numerical correlation and response functions, violating the equilibrium Fluctuation Dissipation relations. The source of memory is identified in the coupling of the tracer velocity $V$ with a spontaneous local velocity field $U$ in the surrounding fluid. Such identification allows us to measure the intruder's fluctuating entropy production as a function of $V$ and $U$, obtaining a neat verification of the Fluctuation Relation.