Prof. Julien Tailleur

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Title: First-order fluctuation-induced phase transitions to collective motion

Abstract: The transition to collective motion is paradigmatic of active matter. Self-propelled particles that stochastically align undergo a transition between a disordered state, at low density and large noise, and an ordered one, at high density and low noise. In the latter phase, particles travel together in a randomly selected direction of space, hence spontaneously breaking its isotropy. The nature of this transition has been at the center of a long-standing debate. Numerical simulations and mean-field continuous descriptions have led to the common belief that, depending on the type of microscopic interactions between

particles, two types of transitions could be observed. When particles interact with their neighbors within a finite-distance, the transition is first order, with a coexistence phase separating the disordered gas and the ordered liquid. On the contrary, when particles interact with `topological' neighbors, the transition is believed…