Codina, JoanMahault, BenoîtDobnikar, JurePagonabarraga Mora, IgnacioShi, Xia-qingChaté, Hugues2023-01-272023-01-272022-05-230031-9007https://hdl.handle.net/2445/192654We 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 counterpropagating 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.6 p.application/pdfeng(c) American Physical Society, 2022Dinàmica molecularMatèria condensada tovaMolecular dynamicsSoft condensed matterinfo:eu-repo/semantics/article7270812023-01-27info:eu-repo/semantics/openAccess