Fluctuation-induced phase separation in metric and topological models of collective motion

TL;DR

This paper investigates how noise influences the transition to collective motion in active matter, revealing that fluctuations can induce phase separation and alter the transition from continuous to discontinuous, even in topological models.

Contribution

It demonstrates that fluctuations cause a density-dependent shift in the onset of order, changing the transition nature in both metric and topological active matter models.

Findings

Fluctuations induce a phase separation scenario.

The transition shifts from continuous to discontinuous due to noise.

Analytical predictions are confirmed by simulations.

Abstract

We study the role of noise on the nature of the transition to collective motion in dry active matter. Starting from field theories that predict a continuous transition at the deterministic level, we show that fluctuations induce a density-dependent shift of the onset of order, which in turns changes the nature of the transition into a phase-separation scenario. Our results apply to a range of systems, including the topological models in which particles interact with a fixed number of nearest neighbors, which were believed so far to exhibit a continuous onset of order. Our analytical predictions are confirmed by numerical simulations of fluctuating hydrodynamics and microscopic models.