We will first show surprising thermodynamic implications for a simple toy model of two nonreciprocally coupled Brownian particles [1]. Then, I will give some insights into how nonreciprocal interactions affect the phases and fluctuations of many-body systems.

First, in binary fluids, nonreciprocal coupling between fluid components can cause the emergence of travelling waves through PT symmetry-breaking phase transitions. We show that fluctuations not only inflate, as in equilibrium criticality, but also develop an asymptotically increasing time-reversal asymmetry [2]. Second, we introduce nonreciprocal coupling in the XY model, where nonreciprocity can lead to the formation of true long-range order [3], but can also induce spatiotemporal chaos that can be regarded as a source of self-generated noise.

[1] Loos and Klapp, NJP (2020).
[2] Suchanek, Kroy, and Loos, PRE (2023), PRE (2023), and PRL (2023).
[3] Loos, Klapp, and Martynec, PRL (2023).