Entropy production rate in thermodynamically consistent flocks

TL;DR

This paper investigates the entropy production rate in a thermodynamically consistent model of flocking particles, revealing how it varies with system configuration, and uncovering singular behaviors in weak propulsion regimes.

Contribution

The study derives an exact correspondence between hydrodynamic and particle-level entropy production, providing new insights into the thermodynamics of flocking transitions.

Findings

EPR is maximal in homogeneous configurations.

EPR decreases in non-homogeneous states with traveling bands.

Weak self-propulsion leads to singular EPR scaling and non-analytic band profiles.

Abstract

We study the entropy production rate (EPR) of aligning self-propelled particles which undergo a flocking transition towards a polarized collective motion. In our thermodynamically consistent lattice model, individual self-propulsion is the exclusive source of irreversibility. We derive the fluctuating hydrodynamics for large system sizes using a controlled coarse-graining: our procedure entails an exact correspondence between the EPR evaluated at the hydrodynamic and particle-based levels. We reveal that EPR is maximal when the system adopts a homogeneous configuration, either apolar or polar, and reduced in the non-homogeneous state where a polar band travels in a apolar background due to strong spatial EPR modulations. By analyzing the latter we also show that asymmetric energetic exchanges occur at the trailing and leading edges, which we map into a thermodynamic cycle in density-polarization space. Finally, we demonstrate that the regime of weak self-propulsion features a singular scaling of EPR, and a non-analyticity of the travelling band profiles.