# Active chiral particles under confinement: surface currents and bulk accumulation phenomena

## TL;DR

This study explores how chiral active particles behave under confinement, revealing surface currents and bulk accumulation phenomena influenced by chirality and confinement geometry, with analytical and numerical insights.

## Contribution

It introduces an extended active Ornstein-Uhlenbeck model for chiral particles under confinement, analyzing their distribution and currents both analytically and numerically.

## Key findings

- Chirality reduces wall accumulation compared to non-chiral particles.
- Chiral particles generate currents parallel to confining walls.
- Bulk accumulation increases with certain confinement conditions.

## Abstract

In this work, we study the stationary behavior of an assembly of independent chiral active particles under confinement by employing an extension of the active Ornstein-Uhlenbeck model. The chirality modeled by means of an effective torque term leads to a drastic reduction of the accumulation near the walls with respect to the case without handedness and to the appearance of currents parallel to the container walls accompanied by a large accumulation of particles in the inner region. In the case of two-dimensional chiral particles confined by harmonic walls, we determine the analytic form of the distribution of positions and velocities in two different situations: a rotationally invariant confining potential and an infinite channel with parabolic walls. Both these models display currents and chirality induced inner accumulation. These phenomena are further investigated by means of a more realistic description of a channel, where the wall and bulk regions are clearly separated. The corresponding current and density profiles are obtained by numerical simulations. At variance with the harmonic models, the third model shows a progressive emptying of the wall regions and the simultaneous enhancement of the bulk population. We explain such a phenomenology in terms of the combined effect of wall repulsive forces and chiral motion and provide a semiquantitative description of the current profile in terms of an effective viscosity of the chiral gas.