The random walk of intermittently self-propelled particles

TL;DR

This paper introduces a comprehensive model for intermittently self-propelled particles, capturing diverse motility behaviors and deriving exact transport properties, with implications for understanding complex biological and physical diffusion processes.

Contribution

It presents a novel dynamical model with arbitrary waiting-time distributions for active and turn states, unifying various known stochastic processes under one framework.

Findings

Derived exact expressions for mean-square displacement and diffusion coefficients.

Identified conditions for subdiffusion and superdiffusion in long-time limits.

Connected the model to known processes like bacterial run-and-tumble and Lévy walks.

Abstract

Motivated by various recent experimental findings, we propose a dynamical model of intermittently self-propelled particles: active particles that recurrently switch between two modes of motion, namely an active run-state and a turn state, in which self-propulsion is absent. The durations of these motility modes are derived from arbitrary waiting-time distributions. We derive the expressions for exact forms of transport characteristics like mean-square displacements and diffusion coefficients to describe such processes. Furthermore, the conditions for the emergence of sub- and superdiffusion in the long-time limit are presented. We give examples of some important processes that occur as limiting cases of our system, including run-and-tumble motion of bacteria, L\'evy walks, hop-and-trap dynamics, intermittent diffusion and continuous time random walks.