Irene Giardina – Sapienza University of Rome
Wednesday, June 4th , 10:45AM DST
Out of equilibrium response and dissipation across scales in flocking systems
Flocking systems are known to be strongly out of equilibrium. Energy input occurs at the individual level to ensure self-propulsion, and the motility in turn contributes to or- dering, strengthening collective motion. However, even beyond ordering, a crucial feature of natural aggregations is response. How, then, off-equilibrium features affect response behavior? I will address this issue both from an empirical and a theoretical perspective. I will first summarize what we know from experiments on natural swarms and flocks and show that out-of-equilibrium effects are stronger in one case than in the other. Then I will consider minimal models of flocking and investigate theoretically and numerically the response behavior. Violations of equilibrium fluctuation-dissipation relations occur both at the local and at the global level and their amount peaks at the ordering transition. Entropy is always produced locally. However, cooperative mechanisms close to the tran- sition spread off equilibrium effects on the whole system, producing an out-of-equilibrium response on the global scale. Our findings elucidate the role of activity and interactions in the cost repartition of collective behavior and explain what observed in experiments on natural living groups.