Emergent Synchronization and Flocking in Purely Repulsive Self-Navigating Particles

TL;DR

This paper investigates how purely repulsive, self-navigating particles can spontaneously form synchronized flocking behavior, revealing emergent collective dynamics without explicit alignment mechanisms.

Contribution

It demonstrates the emergence of synchronized flocking in repulsive active particles and develops an XY model analogy to interpret the phases and defects.

Findings

Particles form system-wide chiral flocks without explicit alignment.

Flocking behavior is robust against noise, polydispersity, and boundaries.

The phase behavior is explained using an XY model analogy.

Abstract

Inspired by groups of animals and robots, we study the collective dynamics of large numbers of active particles, each one trying to get to its own randomly placed target, while avoiding collisions with each other. The particles we study are repulsive homing active Brownian particles (HABPs) - self-propelled particles whose orientation relaxes at a finite rate towards an absorbing target in $2d$ continuous space. For a wide range of parameters, these particles form synchronised system-wide chiral flocks, in spite of the absence of explicit alignment interactions. We show that this dramatic behavior obtains for different system sizes and density, that it is robust against the addition of noise, polydispersity, and bounding walls, and that it can exhibit dynamical topological defects. We develop an analogy to an off-lattice, ferromagnetic XY model, which allows us to interpret the different phases, as well as the topological defects.