Non-equilibrium clustering of self-propelled rods

TL;DR

This paper investigates how self-propelled rods in two dimensions form clusters, revealing that higher packing fractions and aspect ratios promote aggregation, with a mean-field model accurately predicting the clustering transition.

Contribution

It introduces a mean-field model for cluster size distribution that predicts the aspect ratio threshold for clustering based on packing fraction.

Findings

Clustering increases with packing fraction and aspect ratio.

The mean-field model accurately predicts the clustering transition.

The transition aspect ratio follows a specific inverse relation to packing fraction.

Abstract

Motivated by aggregation phenomena in gliding bacteria, we study collective motion in a twodimensional model of active, self-propelled rods interacting through volume exclusion. In simulations with individual particles, we find that particle clustering is facilitated by a sufficiently large packing fraction (eta) or length-to-width ratio (kappa). The transition to clustering in simulations is well captured by a mean-field model for the cluster size distribution, which predicts that the transition values kappa_c of the aspect ratio for a fixed packing fraction is given by kappa_c = C/eta - 1 where C is a constant.