Collective dynamics of self-propelled agents inspired by quorum-sensing bacteria and tissue cells

Imagine a flock of birds flying in splendid coordination, a swarm of bacteria moving in synchronized patterns, or a collection of tissue cells agglomerating to form an organ. Such collective behaviors lie at the heart of active matter, a field within nonequilibrium statistical physics that investigates the dynamics of self-propelled entities such as fish, cells, and artificial particles. In this context, we highlight some of our theoretical contributions to models of particles with persistent motion inspired by biological systems, with an emphasis on underlying conceptual mechanisms. Motivated by experiments with tissue cells, we consider self-aligning adhesive active particles and show how collective ballistic motion explains their fast aggregation kinetics driven by cluster mergers. Moreover, inspired by social microorganisms, we show how motility reduction triggered by quorum sensing can shape motility-induced phase separation in active disks, giving rise to gel-like behavior, long-lived transients, and non-monotonic phase diagrams. Our research advances the understanding of nonequilibrium physics and its implications for biological processes.