A run-and-tumble particle around a spherical obstacle: steady-state distribution far-from-equilibrium

TL;DR

This paper analyzes the steady-state distribution of run-and-tumble particles around a spherical obstacle, revealing activity-induced accumulation and divergence in density profiles, with implications for active particle fluids.

Contribution

It provides an explicit distribution function for highly persistent active particles around a spherical obstacle, extending understanding of non-equilibrium steady states.

Findings

Particles accumulate at the obstacle surface with a delta peak.

Density diverges algebraically near the obstacle.

Derived distribution functions for various active particle models.

Abstract

We study the steady-state distribution function of a run-and-tumble particle evolving around a repulsive hard spherical obstacle. We show that the well-documented activity-induced attraction translates into a delta peak accumulation at the surface of the obstacle accompanied with an algebraic divergence of the density profile close to the obstacle. We obtain the full form of the distribution function in the regime where the typical distance run by the particle between two consecutive tumbles is much larger than the size of the obstacle. This provides an expression for the low-density pair distribution function of a fluid of highly persistent hard-core run-and-tumble particles. This also provides an expression for the steady-state probability distribution of highly-ballistic active Brownian particles and active Ornstein-Ulhenbeck particles around hard spherical obstacles.