Interacting Brownian dynamics in a nonequilibrium particle bath

TL;DR

This paper develops a mesoscopic theory for interacting Brownian particles in a nonequilibrium environment, revealing how nonequilibrium conditions alter effective interactions and noise statistics, with implications for active matter and colloidal systems.

Contribution

It introduces a framework connecting microscopic many-body dynamics to mesoscopic nonequilibrium behavior, highlighting the breakdown of classical relations in active and stirred colloids.

Findings

Effective interactions are modified by nonequilibrium conditions.

Fluctuation-dissipation and action-reaction relations break down.

The theory applies to active Brownian particles and stirred colloids.

Abstract

We set up a mesoscopic theory for interacting Brownian particles embedded in a nonequilibrium environment, starting from the microscopic interacting many-body theory. Using nonequilibrium linear response theory, we characterize the effective dynamical interactions on the mesoscopic scale and the statistics of the nonequilibrium environmental noise, arising upon integrating out the fast degrees of freedom. As hallmarks of nonequilibrium, the breakdown of the fluctuation-dissipation and action-reaction relations for Brownian degrees of freedom are exemplified with two prototypical models for the environment, namely, active Brownian particles and stirred colloids.