Hidden entropy production and work fluctuations in an ideal active gas

TL;DR

This paper investigates entropy production and work fluctuations in an ideal active gas, revealing hidden irreversibility and differences in thermodynamic behavior between models of self-propulsion.

Contribution

It introduces a method to quantify hidden entropy production in active particles and compares models to understand their thermodynamic differences.

Findings

Hidden entropy production maintains persistence in active particles.

Work fluctuations differ significantly between self-propulsion models.

Active matter systems can exhibit non-equilibrium behavior despite ideal conditions.

Abstract

Collections of self-propelled particles that move persistently by continuously consuming free energy are a paradigmatic example of active matter. In these systems, unlike Brownian "hot colloids", the breakdown of detailed balance yields a continuous production of entropy at steady state, even for an ideal active gas. We quantify the irreversibility for a non-interacting active particle in two dimensions by treating both conjugated and time-reversed dynamics. By starting with underdamped dynamics, we identify a hidden rate of entropy production required to maintain persistence and prevent the rapidly relaxing momenta from thermalizing, even in the limit of very large friction. Additionally, comparing two popular models of self-propulsion with identical dissipation on average, we find that the fluctuations and large deviations in work done are markedly different, providing thermodynamic insight into the varying extents to which macroscopically similar active matter systems may depart from equilibrium.