Emergence of collective motion in a model of interacting Brownian particles

TL;DR

This paper demonstrates that collective motion and flocking can emerge in a system of Brownian particles with local velocity alignment, without requiring self-propulsion, by analyzing underdamped particle dynamics.

Contribution

It shows that self-propulsion is not necessary for flocking, expanding understanding of collective behavior in particle systems.

Findings

Transition from equilibrium to collective motion with long-range order

Presence of giant number fluctuations in the ordered phase

Flocking occurs without self-propulsion in underdamped systems

Abstract

By studying a system of Brownian particles, interacting only through a local social-like force (velocity alignment), we show that self-propulsion is not a necessary feature for the flocking transition to take place as long as underdamped particle dynamics can be guaranteed. Moreover, the system transits from stationary phases close to thermal equilibrium, with no net flux of particles, to far-from-equilibrium ones exhibiting collective motion, long-range order and giant number fluctuations, features typically associated to ordered phases of models where self-propulsion is considered.