Apparent anomalous diffusion and non-Gaussian distributions in a simple mobile-immobile transport model with Poissonian switching

TL;DR

This study reveals complex transport behaviors such as transient anomalous diffusion and non-Gaussian distributions in a simple mobile-immobile particle switching model, with implications for understanding transport in biological and complex systems.

Contribution

It demonstrates that even with Poissonian switching, the model exhibits rich dynamics including anomalous diffusion and non-Gaussian displacement distributions, extending understanding of such processes.

Findings

Transient anomalous diffusion occurs when mean binding time exceeds mobile time.

Particle displacements follow a Laplace distribution at intermediate times.

Mean squared displacement shows a plateau and cubic short-time dependence for immobile tracers.

Abstract

We analyse mobile-immobile transport of particles that switch between the mobile and immobile phases with finite rates. Despite this seemingly simple assumption of Poissonian switching we unveil a rich transport dynamics including significant transient anomalous diffusion and non-Gaussian displacement distributions. Our discussion is based on experimental parameters for tau proteins in neuronal cells, but the results obtained here are expected to be of relevance for a broad class of processes in complex systems. Concretely, we obtain that when the mean binding time is significantly longer than the mean mobile time, transient anomalous diffusion is observed at short and intermediate time scales, with a strong dependence on the fraction of initially mobile and immobile particles. We unveil a Laplace distribution of particle displacements at relevant intermediate time scales. For any initial fraction of mobile particles, the respective mean squared displacement displays a plateau. Moreover, we demonstrate a short-time cubic time dependence of the mean squared displacement for immobile tracers when initially all particles are immobile.