Abstract

Recent years witnessed a significant interest in physical, biological and engineering properties of self-propelled particles, such as bacteria or synthetic microswimmers. One of the most striking features of interacting microswimmers is the appearance of collective motion: at sufficiently high densities the system is characterised by jets and vortices comprising many individual microswimmers. The transition to collection motion in dilute suspension of microswimmers interacting through long-range velocity fields is usually described in terms of a mean-field kinetic theory that predicts the onset of collective motion in two- and three-dimensional bulk systems. Here, we formulate a stochastic kinetic theory for dilute microswimer suspensions and demonstrate that its predictions differ significantly from its mean-field counterpart. Our results bear important implications for the general description of the transition to collective motion in two-dimensional systems.