Dynamical structures in phase-separating nonreciprocal polar active mixtures

Nonreciprocal systems exhibit diverse dynamical phases whose character depends on the type and degree of nonreciprocity. In this study, we theoretically investigate dynamical structures in a mixture of nonreciprocally aligning polar active particles with repulsion, focusing on the performance on (and connection between) different levels of description. Linear stability analyses of the associated continuum model predict a profound influence of nonreciprocity, leading to phase separation, (anti-)flocking, and asymmetric clustering behavior. On the microscopic level, particle simulations confirm the emergence of these dynamical phases and allow for a more in-depth investigation of (microscopic) properties, including orientational correlations and susceptibilities. The drastic impact of orientational couplings alone on the density dynamics is demonstrated in particle simulations without repulsion, where nonreciprocal alignment leads to the asymmetric formation of single-species polarized clumps. Overall, our findings demonstrate that certain dynamical properties, like a chase-and-run behavior in the asymmetrical clustering phase, are overlooked in mean-field continuum theory, making microscopic simulations an indispensable tool for studying the effects of nonreciprocal alignment couplings.