Dynamics of a massive intruder in a homogeneously driven granular fluid

TL;DR

This paper investigates the motion of a massive intruder in a driven granular fluid, revealing a transition from simple Brownian motion to a memory-influenced regime with broken fluctuation-dissipation relations.

Contribution

It introduces a model describing the intruder's dynamics, capturing the transition from memoryless to memory-influenced behavior in granular fluids.

Findings

At low volume fractions, intruder exhibits Brownian motion with simple relations.

At higher volume fractions, velocity correlates with local fluid flow, requiring a generalized Langevin approach.

Fluctuation-Dissipation relation breaks down, and entropy flux obeys Fluctuation Relation.

Abstract

A massive intruder in a homogeneously driven granular fluid, in dilute configurations, performs a memory-less Brownian motion with drag and temperature simply related to the average density and temperature of the fluid. At volume fraction $\sim 10-50%$ the intruder's velocity correlates with the local fluid velocity field: such situation is approximately described by a system of coupled linear Langevin equations equivalent to a generalized Brownian motion with memory. Here one may verify the breakdown of the Fluctuation-Dissipation relation and the presence of a net entropy flux - from the fluid to the intruder - whose fluctuations satisfy the Fluctuation Relation.