Quantifying dissipation in flocking dynamics: When tracking internal states matters

TL;DR

This paper introduces a lattice model for flocking particles that accounts for internal states affecting diffusion, revealing how dissipation varies with interaction strength and emphasizing the importance of internal state tracking.

Contribution

It presents a thermodynamically consistent lattice model capturing flocking transition and dissipation behavior, linking microscopic and macroscopic dissipation through local detailed balance.

Findings

Dissipation is maximal at weak interactions and underestimated when internal states are ignored.

Strong interactions reduce dissipation, allowing partial inference to capture most of it.

Macroscopic dissipation matches microscopic dissipation after coarse-graining.

Abstract

Aligning self-propelled particles undergo a nonequilibrium flocking transition from apolar to polar phases as their interactions become stronger. We propose a thermodynamically consistent lattice model, in which the internal state of the particles biases their diffusion, to capture such a transition. Changes of internal states and jumps between lattice sites obey local detailed balance with respect to the same interaction energy. We unveil a crossover between two regimes: for weak interactions, the dissipation is maximal, and partial inference (namely, based on discarding the dynamics of internal states) leads to a severe underestimation; for strong interactions, the dissipation is reduced, and partial inference captures most of the dissipation. Finally, we reveal that the macroscopic dissipation, evaluated at the hydrodynamic level, coincides with the microscopic dissipation upon coarse-graining. We argue that this correspondence stems from a generic mapping of active lattice models with local detailed balance into a specific class of non-ideal reaction-diffusion systems.