Spontaneous Rotation of a Symmetric Inclusion in Chiral Active Bath

TL;DR

This paper demonstrates that a symmetric passive object can spontaneously rotate in a chiral active particle bath due to interaction-driven symmetry breaking, revealing new mechanisms of motion in active matter.

Contribution

It uncovers how symmetric passive inclusions can spontaneously rotate in chiral active baths without shape anisotropy or external forces, through simulation-based analysis.

Findings

Persistent rotation occurs despite geometric symmetry.

Two regimes of rotation identified: density gradient-driven and impact frequency-driven.

Symmetry breaking arises from nonequilibrium interactions, not shape or external forces.

Abstract

We study the dynamics of a circular passive inclusion, termed a torquer, in a bath of chiral active Brownian particles. Despite being geometrically symmetric and non-motile, the torquer exhibits persistent rotation due to spatially inhomogeneous torques arising from angularly biased collisions with active particles. This interaction-driven symmetry breaking does not rely on shape anisotropy or external forcing. Through simulations, we identify two distinct regimes of rotation: one dominated by density gradients at low chirality, and another by increased impact frequency at high chirality. Our results highlight how nonequilibrium interactions in chiral active media can induce motion in symmetric objects, offering a new perspective on symmetry breaking in active systems.