Equilibrium mappings in polar-isotropic confined active particles

TL;DR

This paper investigates the extent to which equilibrium mapping techniques can describe polar-isotropic active particles confined by boundaries, revealing limitations due to boundary geometry affecting local free energy and behavior independence.

Contribution

It analyzes how boundary shape influences the applicability of equilibrium mappings in polar-isotropic active systems, highlighting constraints posed by concave boundary regions.

Findings

Concave boundary regions cause nonlocal density dependence.

Equilibrium mappings are limited by boundary geometry effects.

Behavior becomes strongly dynamics-dependent near certain boundaries.

Abstract

Despite their fundamentally non-equilibrium nature, the individual and collective behavior of active systems with polar propulsion and isotropic interactions (polar-isotropic active systems) are remarkably well captured by equilibrium mapping techniques. Here we examine two signatures of equilibrium systems -- the existence of a local free energy function and the independence of the coarse- grained behavior on the details of the microscopic dynamics -- in polar-isotropic active particles confined by hard walls of arbitrary geometry at the one-particle level. We find that boundaries that possess concave regions make the density profile strongly dynamics-dependent and give it a nonlocal dependence on the geometry of the confining box. This in turn constrains the scope of equilibrium mapping techniques in polar-isotropic active systems.