Local interactions in active matter are reinforced by spatial structure

Abstract: The flocking of self-propelled particles in heterogeneous environments is relevant to both natural and artificial systems. The Vicsek model is a canonical choice to investigate such systems due to the minimal number of parameters required to define flocking. Prior research on the Vicsek model has investigated the effects of interaction rules, particle speed, and obstacle packing on the flocking behavior, but the effect of interaction radius remains an open question. Unlike obstacle-free domains, the locality of interactions not only affects how quickly the system can become polarized, but also how well the flocks can align or realign after colliding with obstacles. In this letter, we delve into this subtle relationship that exists in the scale of the perception of Vicsek particles in the presence of obstacles. We demonstrate that the presence of obstacles impacts group density, which provides the basis to identify distinct phases for collective behavior. This leads to the counter-intuitive result that obstacles, while generally confounding for macroscopic order, may enable global order even as noise in the system increases.