Emergence of agent swarm migration and vortex formation through inelastic collisions

Biologically inspired models of self-propelled interacting agents display a wide variety of collective motion such as swarm migration and vortex formation. In these models, active interactions among agents are typically included such as velocity alignment and cohesive and repulsive forces that represent agents' short- and long-range 'sensing' capabilities of their environment. Here, we show that similar collective behaviors can emerge in a minimal model of isotropic agents solely due to a passive mechanism - inelastic collisions among agents. The model dynamics shows a gradual velocity correlation build-up into the collective motion state. The model displays a discontinuous transition of collective motion with respect to noise and exhibits several collective motion types such as vortex formation, swarm migration and also complex spatio-temporal group motion. This model can be regarded as a hybrid model, connecting granular materials and agent-based models.