Young Researchers Workshop: Kinetic descriptions in theory and applications

Three-body interactions drive the transition to polar order in a simple flocking model

Purba Chatterjee

University of Illinois at Urbana-Champaign


Active systems are characterized by a discontinuous flocking transition from a disordered isotropic state to a polar ordered state with increasing density and decreasing noise. A large class of mesoscopic or macroscopic theories for flocking are coarse grained from microscopic models that feature binary interactions as the chief aligning mechanism. However as was recently shown, at the high densities at which the system flocks, binary interactions are too weak to account for the ordering transition. In this work, we show that to the lowest order, three-body interactions are not only necessary but also sufficient to capture the full phenomenology of flocking.