Memory Effects in Active Particles with Exponentially Correlated Propulsion

Abstract

The Ornstein--Uhlenbeck Particle (OUP) model imagines a microscopic swimmer propelled by an active force which is correlated with itself on a finite time-scale. Here we investigate the influence of external potentials on an ideal suspension of OUPs, in both one and two spatial dimensions, with particular attention paid to the pressure exerted on "confining walls". We employ a mathematical connection between the local density of OUPs and the statistics of their propulsion force to demonstrate the existence of an equation of state in one dimension. In higher dimensions we show that active particles generate a non-conservative force field in the surrounding medium. A simplified far-from-equilibrium model is proposed to account for OUP behaviour in the vicinity of potentials. Building on this, we interpret simulations of OUPs in more complicated situations involving asymmetrical and spatially curved potentials, characterising the inhomogeneous local stresses which result in terms of competing active length-scales.