Anisotropic active Brownian particle with a fluctuating propulsion force

TL;DR

This paper introduces a 2D active Brownian particle model with nonthermal force fluctuations, revealing anisotropic effects, coupling between translational and rotational motion, and mass-dependent drift, impacting long-term diffusivity.

Contribution

It presents a novel 2D ABP model with nonthermal force fluctuations, highlighting anisotropic effects and force-position independent diffusivity contributions.

Findings

Fluctuating force causes a fluctuating torque and coupling in diffusion tensor.

Anisotropic particles exhibit a mass-dependent noise-induced drift.

Long-time diffusivity includes a force-position independent contribution.

Abstract

The active Brownian particle (ABP) model describes a swimmer, synthetic or living, whose direction of swimming is a Brownian motion. The swimming is due to a propulsion force, and the fluctuations are typically thermal in origin. We present a 2D model where the fluctuations arise from nonthermal noise in a propelling force acting at a single point, such as that due to a flagellum. We take the overdamped limit and find several modifications to the traditional ABP model. Since the fluctuating force causes a fluctuating torque, the diffusion tensor describing the process has a coupling between translational and rotational degrees of freedom. An anisotropic particle also exhibits a mass-dependent noise-induced drift, which does not disappear in the overdamped limit. We show that these effects have measurable consequences for the long-time diffusivity of active particles, in particular adding a contribution that is independent of where the force acts.