Characteristics of phase transitions in dry aligning active matter

Abstract Active matter is a non-equilibrium condensed system consisting of self-propelled particles capable of converting stored or ambient energy into collective motion. Typical active matter systems include cytoskeleton biopolymers, swimming bacteria, artificial swimmers, and animal herds. In contrast to wet active matter, dry active matter is an active system characterized by the absence of significant hydrodynamic interactions and conserved momentum. In dry active matter, the role of surrounding fluids is providing viscous friction at low Reynolds numbers and can be neglected at high Reynolds numbers. This review offers a comprehensive overview of recent experimental, computational, and theoretical advances in understanding phase transitions and critical phenomena in dry aligning active matter, including polar particles, self-propelled rods, active nematics, and their chiral counterparts. Various ways of determining phase transition points as well as non-equilibrium phenomena, such as collective motion, cluster formation, and creation and annihilation of topological defects are reviewed.