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

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.