Order-disorder transition in repulsive self-propelled particle systems

TL;DR

This paper investigates how repulsive self-propelled particles transition from disordered to ordered collective motion, revealing the role of damping and density fluctuations through simulations and binary scattering analysis.

Contribution

It introduces a binary scattering approach to predict order-disorder transitions in self-propelled particle systems, extending analysis to finite densities.

Findings

Disordered states spontaneously develop into collective motion with density fluctuations.

Strong rotational damping induces abrupt order-disorder transitions after metastable periods.

Binary scattering predicts transitions at dilute limits but diverges at higher densities due to many-body effects.

Abstract

We study the collective dynamics of repulsive self-propelled particles. The particles are governed by coupled equations of motion that include polar self-propulsion, damping of velocity and of polarity, repulsive particle-particle interaction, and deterministic dynamics. Particle dynamics simulations show that the collective coherent motion with large density fluctuations spontaneously emerges from a disordered, isotropic state. In the parameter region where the rotational damping of polarity is strong, the systems undergoes an abrupt shift to the absorbing ordered state after a waiting period in the metastable disordered state. In order to obtain a simple understanding of the mechanism underlying the collective behavior, we analyze binary particle scattering process. We show that this approach correctly predicts the order-disorder transition at dilute limit. The same approach is expanded for finite densities, although it disagrees with the result from many-particle simulations due to many-body correlations and density fluctuations.