Escape of a passive particle from activity-induced energy landscape: Emergence of slow and fast effective diffusion

Abstract

Spontaneous persistent motions driven by active processes play a central role to maintain the living cells far from equilibrium. In the majority of the research works, the steady state dynamics of an active system has been described in terms of an effective temperature. By contrast, we have examined a prototype model for diffusion in an activity-induced rugged energy landscape to describe the slow dynamics of a tagged particle in a dense active environment. The expression for the mean escape time from the active rugged energy landscape holds only in the limit of low activity and the mean escape time from the rugged energy landscape increases with activity. The precise form of the active correlation will determine whether the mean escape time will depend on the persistence time or not. The active rugged energy landscape approach also allows an estimate of non-equilibrium effective diffusivity characterizing the slow diffusive motion of the tagged particle due to activity. On the other hand, in a dilute environment, high activity augments the diffusion of the tagged particle. The enhanced diffusion can be attributed to an effective temperature, higher than the ambient temperature and is used to calculate the Kramers' mean escape time, which decreases with activity. Our results have direct relevance to recent experiments on tagged particle diffusion in condensed phases. I. INTRODUCTIONSystems composed of active particles represent a class of driven non-equilibrium systems in which the driving forces are direct, isotropic and controlled locally rather than globally [1,2]. They can either be found in biological systems such as bacterial colonies [3], motile cells in tissues [4], cytoskeleton in living cells [5] or are realized artificially such as catalytic Janus particles [6]. While the former are typically self-propelled by the chemical energy