PREPRINT
A344B802-FE18-4F43-8543-85ABB1AB62E5

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

Jean-Baptiste Fouvry
arXiv:2207.05349

Submitted on 12 July 2022

## 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.

## Preprint

Comment: 9 pages, 1 figure, submitted to APS

Subjects: Condensed Matter - Statistical Mechanics; Astrophysics - Astrophysics of Galaxies