Starts 12 Dec 2019 11:00
Ends 12 Dec 2019 12:00
Central European Time
ICTP
Leonardo Building - Luigi Stasi Seminar Room
Animal groups on the move are a paradigmatic example of collective behavior in social species in which the tools of statistical physics can be fruitfully used. I will present an experimental and theoretical study of spontaneous rapid collective turns in natural flocks of starlings in which we find a sound-like propagation of the turning decision across the flock with no damping of information. This is in contrast with standard theories of collective animal behavior based on alignment, which predict a much slower, diffusive spread of information. We propose a novel theory for propagation of orientation in flocks whose key ingredient is the existence of a conserved spin current generated by the gauge symmetry of the system. Moreover, our analysis reveals that spontaneous collective turns are triggered by persistent localized fluctuations in the travel direction of some individuals in the flock. Two crucial ingredients which enhance the effect of such noise leading to collective changes of state are: the non-symmetric nature of interaction between individuals and the presence of heterogeneities in the topology of the interaction network.