Signatures of irreversibility in microscopic models of flocking

Flocking is one of the most startling collective behaviors in active matter. The emergence of collective motion in d=2 occurring in these systems is a genuine non-equilibrium feature. It marks a fundamental difference with classical passive models for ferromagnets and requires irreversibility.

We investigate how the interplay of alignment interaction and self-propulsion in Vicsek-like dynamics leads to the breakdown of detailed balance and constrains asymmetries in the steady-state distribution of the many-body system. We quantify the departure from equilibrium through measurements of the entropy production rate on numerical simulations of polar ABPs, considering two variants of the model, with metric and topological interaction rules. It is known that they give rise to different kinds of phase transitions and macroscopic configurations, and we find that different signatures of irreversibility can be identified in the two cases.