Driven active matter: Fluctuations and a hydrodynamic instability

Abstract

Wet active matter in the presence of an imposed temperature gradient, or chemical potential gradient, is considered. It is shown that there is a type of convective instability that is caused by a (negative) activity parameter. Physically this corresponds to active fluids with contractual stress. In this nonequilibrium steady state the singular generic long-ranged correlations are computed and compared and contrasted with the analogous results in a passive fluid. In addition, the singular nonequilibrium Casimir pressure or force is determined. The fluid motion above the instability is determined by generalizing the Lorenz equations for the Rayleigh-Benard problem in a passive fluid to Lorenz-like equations to describe this instability.