title: Onset of collective and cohesive motion.
abstract: We study the onset of collective motion, with and without cohesion, of groups of noisy self-propelled particles interacting locally. We find that this phase transition, in two space dimensions, is always discontinuous, including for the minimal model of Vicsek et al. [Phys. Rev. Lett. 75, 1226 (1995)]] for which a nontrivial critical point was previously advocated. We also show that cohesion is always lost near onset, as a result of the interplay of density, velocity, and shape fluctuations.
authors.affiliation: CEA-Service de Physique de l'Etat Condensé, CEN Saclay, 91191 Gif-sur-Yvette, France.
authors.forename: Guillaume
authors.initials: G
authors.lastname: Grégoire
authors.forename: Hugues
authors.initials: H
authors.lastname: Chaté
mesh_terms: D000818:Animals; D006801:Humans; D008962:Models, Theoretical; D009038:Motion