Nonequilibrium fluctuations and enhanced diffusion of a driven particle in a dense environment

TL;DR

This paper investigates how a driven tracer particle diffuses in a dense environment, revealing nonequilibrium effects like enhanced diffusivity due to crowding and external forces, using a lattice-based stochastic model.

Contribution

It introduces a decoupling approximation that accurately captures fluctuations of a driven tracer in dense environments, extending beyond mean-field approaches.

Findings

Enhanced diffusivity due to crowding and external driving

Approximation becomes exact in high- and low-density limits

Fluctuations analyzed in arbitrary dimensions and boundary conditions

Abstract

We study the diffusion of a tracer particle driven out-of-equilibrium by an external force and traveling in a dense environment of arbitrary density. The system evolves on a discrete lattice and its stochastic dynamics is described by a master equation. Relying on a decoupling approximation that goes beyond the naive mean-field treatment of the problem, we calculate the fluctuations of the position of the tracer around its mean value on a lattice of arbitrary dimension, and with different boundary conditions. We reveal intrinsically nonequilibrium effects, such as enhanced diffusivity of the tracer induced both by the crowding interactions and the external driving. We finally consider the high-density and low-density limits of the model and show that our approximation scheme becomes exact in these limits.