Stochastic Forces Enhance Tracer Diffusion in Non-motile Active Matter

TL;DR

This paper demonstrates that stochastic reciprocal interactions in active matter systems can significantly enhance tracer particle diffusion, revealing a new mechanism for increased mobility in non-equilibrium suspensions.

Contribution

It introduces a theoretical framework showing how reciprocal stochastic forces alone can boost diffusion without self-propulsion or non-reciprocity.

Findings

Reciprocal stochastic interactions create active suspensions with higher effective temperature.

Enhanced tracer diffusion occurs due to these stochastic forces in dense suspensions.

The model predicts increased diffusivity in non-equilibrium active matter systems.

Abstract

Stochasticity is a defining feature of the pairwise forces governing interactions in biological systems-from molecular motors to cell-cell adhesion-yet its consequences on large-scale dynamics remain poorly understood. Here, we show that reciprocal but randomly fluctuating interactions between particles create active suspensions which can enhance the diffusion of an external tracer particle, even in the absence of self-propulsion or non-reciprocity. Starting from a lattice model with pairwise dynamics that minimally break detailed balance, we derive a coarse-grained dynamical theory for spatio-temporal density fluctuations and reveal an elevated effective temperature at short wavelengths. We then compute the self-diffusion coefficient of a tracer particle weakly coupled to our active fluid, demonstrating that purely reciprocal stochastic interactions provide a distinct and generic route to enhanced diffusivity in dense non-equilibrium suspensions.