From scalar to polar active matter: Connecting simulations with mean-field theory

TL;DR

This paper explores the phase behavior of self-propelled elliptical particles, connecting scalar and polar active matter through simulations and mean-field theory, revealing how aspect ratio influences phase transitions.

Contribution

It introduces a unified mean-field framework that captures the transition from scalar to polar active matter by identifying key effective parameters.

Findings

Discoid particles exhibit phase separation.

Elongated particles form polar bands.

Two effective parameters suffice for mean-field description.

Abstract

We study numerically the phase behavior of self-propelled elliptical particles interacting through the "hard" repulsive Gay-Berne potential at infinite P\'eclet number. Changing a single parameter, the aspect ratio, allows to continuously go from discoid active Brownian particles to elongated polar rods. Discoids show phase separation, which changes to a cluster state of polar domains, which then form polar bands as the aspect ratio is increased. From the simulations, we identify and extract the two effective parameters entering the mean-field description: the force imbalance coefficient and the effective coupling to the local polarization. These two coefficients are sufficient to obtain a complete and consistent picture, unifying the paradigms of scalar and polar active matter.