How far from equilibrium is active matter?

TL;DR

This paper investigates the nonequilibrium nature of active matter, demonstrating that systems with small persistent noise exhibit equilibrium-like properties, including vanishing entropy production and effective fluctuation-dissipation relations.

Contribution

It provides a perturbative analysis showing that active matter with short persistence times behaves as if in equilibrium, offering new insights into their energetic and dynamical properties.

Findings

Entropy production rate vanishes at small persistence times.

Active systems obey an effective fluctuation-dissipation theorem.

Active matter can be modeled as in equilibrium with a visco-elastic bath but driven by non-conservative forces.

Abstract

Active matter systems are driven out of thermal equilibrium by a lack of generalized Stokes-Einstein relation between injection and dissipation of energy at the microscopic scale. We consider such a system of interacting particles, propelled by persistent noises, and show that, at small but finite persistence time, their dynamics still satisfy a time-reversal symmetry. To do so, we compute perturbatively their steady-state measure and show that, for short persistent times, the entropy production rate vanishes. This endows such systems with an effective Fluctuation-Dissipation theorem akin to that of thermal equilibrium systems. Last we show how interacting particle systems with viscous drags and correlated noises can be seen as in equilibrium with a visco-elastic bath but driven out of equilibrium by non-conservative forces, hence providing an energetic insight on the departure of active systems from equilibrium.