Breakdown of Emergent Chiral Order and Defect Chaos in Nonreciprocal Flocks

TL;DR

This paper demonstrates that chiral order in nonreciprocal flocking systems is unstable due to defect proliferation, leading to chaotic dynamics with nonuniversal scaling behavior.

Contribution

It combines simulations and continuum theory to reveal how antisymmetric couplings destabilize chiral order through defect chaos.

Findings

Chiral order is generically unstable in nonreciprocal flocks.

Topological defects cause chaotic, scale-free fluctuations below a certain length scale.

Nonuniversal scaling exponents emerge from density-order coupling.

Abstract

We show that chiral order in two-dimensional nonreciprocal flocking mixtures is generically unstable. Combining large-scale agent-based simulations with a coarse-grained continuum description, we demonstrate that rotating chiral states emerging from antisymmetric couplings are destroyed by the proliferation of topological defects. The resulting dynamics is spatiotemporally chaotic and characterized by a finite correlation length that diverges as nonreciprocity vanishes. On length scales below this cutoff, density and orientational order fluctuations remain scale-free, but the associated scaling exhibits nonuniversal exponents. We attribute this atypical behavior to the coupling between density and order, which causes topological defects to act as persistent sources of nonlinear fluctuations.