Hidden nonreciprocity as a stabilizing effective potential in active matter

Abstract

Nonreciprocal interactions are known to produce distinctive dynamics in active matter. To shed light on how the stationary state of such systems is affected by breaking reciprocity, we consider active Ornstein-Uhlenbeck particles coupled nonreciprocally by a transverse force, which is perpendicular to the gradient of the interaction energy. Focusing on the steady-state distribution of positions, we show that the nonreciprocal coupling helps keep the system at its stable configurations, including not only energy minima but also nonequilibrium configurations stabilized by the persistent noise which propels the particles. In contrast, the transverse force would not change the stationary distribution at all if the noise were thermal. For a variety of active systems, we demonstrate the stabilizing role of the nonreciprocity, finding that it stiffens springs, aligns spins, improves associative memory, and enhances motility-induced phase separation.