The simplest extensions of single-particle dynamics in a momentum-conserving active fluid—an active suspension of two colloidal particles or a single particle confined by a wall—exhibit strong departures from Boltzmann behavior, resulting in either a breakdown of an effective temperature description or a steady state with nonzero-entropy production rate. This is a consequence of hydrodynamic interactions that introduce multiplicative noise in the stochastic description of particle positions. This results in fluctuation-induced interactions that depend on distance as a power law. We find that the dynamics of activated colloids in a passive fluid, with stochastic forcing localized on the particle, is different from that of passive colloids in an active fluctuating fluid.

%B Phys. Rev. E %V 100 %P 062602 %8 12/2019 %G eng %R 10.1103/PhysRevE.100.062602