Separazione di fase tra fase a bolle e fase a cluster nella materia attiva

Active matter is characterized by particles that are self-propelled, i.e. that are able to move or exert mechanical forces by continually consuming energy, bypassing the laws of equilibrium thermodynamics. Self-propelled particles tend to accumulate where they move more slowly, undergoing bulk liquid-vapor phase separation due to their motility (Motility Induced Phase Separation). In experiments and large scale simulations more complex steady states are also seen, comprising a dynamic population of dense clusters in a sea of vapor, or dilute bubbles in a liquid. In the literature, several mechanisms for the emergence of cluster phases have been suggested, based on long range interactions. Here, I show that this phenomenon emerges generically in active matter and do not require system-specific explanations, by writing a field theory for the density field that includes active currents, consisting of a mixture of irrotational and rotational contributions, that break detailed balance. Afterwards, I show how these active terms arise by a coarse-graining of a microscopic model. Finally, I outline the results of my simulations.