Nematic Torques in Scalar Active Matter: when Fluctuations Favor Polar Order and Persistence

TL;DR

This paper investigates how nematic torques influence scalar active matter, revealing that they can promote or inhibit phase separation by fluctuation-driven effects, and enhance particle persistence and boundary accumulation.

Contribution

It introduces a fluctuation-induced mechanism showing nematic torques can control phase behavior and persistence in scalar active matter, expanding understanding of active matter physics.

Findings

Nematic torques can induce or prevent phase separation.

Nematic torques increase particle persistence length.

Nematic torques enhance boundary accumulation and oppose demixing.

Abstract

We study the impact of nematic alignment on scalar active matter in the disordered phase. We show that nematic torques control the emergent physics of particles interacting via pairwise forces and can either induce or prevent phase separation. The underlying mechanism is a fluctuation-induced renormalization of the mass of the polar field that generically arises from nematic torques. The correlations between the fluctuations of the polar and nematic fields indeed conspire to increase the particle persistence length, contrary to what phenomenological computations predict. This effect is generic and our theory also quantitatively accounts for how nematic torques enhance particle accumulation along confining boundaries and opposes demixing in mixtures of active and passive particles.