Gulliver Seminar : Sarah Loos (Cambridge University)

Irreversibility in fluctuating nonreciprocal systems

While the action-reaction principle dictates all fundamental physical interactions, the dynamics we effectively observe in complex nonequilibrium systems ubiquitously breaks reciprocity on various scales. I will first show that even for a simple system of two nonreciprocally coupled Brownian particles, nonreciprocity can have surprising thermodynamic implications, such as generating heat flows against a temperature gradient [1]. I will then discuss fluctuations near nonreciprocal phase transitions. Using fluctuating field theories, we show for a wide class of models that close to such transitions, fluctuations not only inflate, as in equilibrium criticality, but also develop an asymptotically increasing time-reversal asymmetry and associated surging entropy production [2,3]. The formation of dissipative patterns and the emergence of irreversible fluctuations can both be attributed to a mechanism of mode coupling in the vicinity of critical exception points. For a nonreciprocal Cahn-Hilliard model, we show that this manifests itself in actively propelled interfaces whose dynamics can be mapped to the motion of a single microswimmer.