Small Obstacle in a Large Polar Flock
arXiv:2112.08410 · doi:10.1103/PhysRevLett.128.218001
Abstract
We show that arbitrarily large polar flocks are susceptible to the presence of a single small obstacle. In a wide region of parameter space, the obstacle triggers counter-propagating dense bands leading to reversals of the flow. In very large systems, these bands interact yielding a never-ending chaotic dynamics that constitutes a new disordered phase of the system. While most of these results were obtained using simulations of aligning self-propelled particles, we find similar phenomena at the continuous level, not when considering the basic Toner-Tu hydrodynamic theory, but in simulations of truncations of the relevant Boltzmann equation.
arXiv comment5 pages, 4 figures, Supplementary information. Movies available from authors on request
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