Kinetic theory of one-dimensional inhomogeneous long-range interacting $N$-body systems at order $1/N^{2}$ without collective effects

TL;DR

This paper derives a new $1/N^{2}$ collision operator for one-dimensional inhomogeneous long-range systems without collective effects, providing insights into their relaxation processes and entropy behavior.

Contribution

It introduces an explicit $1/N^{2}$ collision operator for specific 1D long-range systems where the Balescu--Lenard equation vanishes, advancing understanding of their kinetic theory.

Findings

The $1/N^{2}$ operator satisfies an $H$-theorem for Boltzmann entropy.

Comparison with N-body simulations confirms the operator's predictions.

Identifies interaction potentials where the $1/N^{2}$ collision operator vanishes.

Abstract

Long-range interacting systems irreversibly relax as a result of their finite number of particles, $N$. At order $1/N$, this process is described by the inhomogeneous Balescu--Lenard equation. Yet, this equation exactly vanishes in one-dimensional inhomogeneous systems with a monotonic frequency profile and sustaining only 1:1 resonances. In the limit where collective effects can be neglected, we derive a closed and explicit $1/N^{2}$ collision operator for such systems. We detail its properties highlighting in particular how it satisfies an $H$-theorem for Boltzmann entropy. We also compare its predictions with direct $N$-body simulations. Finally, we exhibit a generic class of long-range interaction potentials for which this $1/N^{2}$ collision operator exactly vanishes.