Coordination of self-propelled particles through external leadership

We study the organization of a group of self-propelled particles induced by a mobile external leader particle. Group particles interact with each other and the leader through pairwise potentials. Simulation results in two dimensions reveal the existence of a unique variety of particle aggregation states, spanning from highly polarized tracking of the leader to coherent milling about it. Transition between aggregation states is elicited by a complex interplay among particle energy, group size, interaction strength, and leader mobility. These findings shed light on the structure and organization of biological groups influenced by external aggregation devices, environmental stimuli, or trained individuals taking the lead.