Synchronization and exceptional points in nonreciprocal active polar mixtures

TL;DR

This paper investigates how nonreciprocal interactions in active polar mixtures lead to diverse collective behaviors, including chiral motion and chimera-like states, with exceptional points playing a key role in these dynamics.

Contribution

It provides a minimal theoretical framework linking nonreciprocal couplings, exceptional points, and observable particle dynamics in active matter.

Findings

Nonreciprocity induces chiral particle motion.

No complete homogeneous synchronization observed.

Exceptional points correlate with peak nonreciprocity effects.

Abstract

Many active matter systems consist of different particle types that interact via nonreciprocal couplings. Such nonreciprocal couplings can lead to the spontaneous emergence of time-dependent states that break parity-time symmetry. On the field-theoretical level, the transition to these states is marked by so-called exceptional points. However, their precise impact on observable particle dynamics remains poorly understood. In this study, we address this gap by providing a scale-bridging view of a minimal active mixture with nonreciprocal polar interactions. We find that nonreciprocity induces chiral motion on the particle level, yet no full, homogeneous synchronization. Instead, we observe various behaviors, ranging from fully synchronized clusters to chimera-like states. The nonreciprocity-induced spontaneous chirality increases with the degree of nonreciprocity and peaks at coupling strengths associated with exceptional points.