Uniform propagation of chaos for Kac's 1D particle system

TL;DR

This paper establishes uniform propagation of chaos for Kac's 1D particle system, providing explicit polynomial convergence rates in Wasserstein distance for both energy and non-energy systems.

Contribution

The paper proves uniform in time propagation of chaos with explicit polynomial rates in N for Kac's 1D system, using a novel parametrization and coupling techniques.

Findings

Rates of order N^{-1/3} for convergence in Wasserstein distance.

Uniform propagation of chaos holds for both squared and non-squared particle systems.

Requires initial moments of order 4+epsilon for convergence.

Abstract

In this paper we study Kac's 1D particle system, consisting of the velocities of $N$ particles colliding at constant rate and randomly exchanging energies. We prove uniform (in time) propagation of chaos in Wasserstein distance with explicit polynomial rates in $N$, for both the squared (i.e., the energy) and non-squared particle system. These rates are of order $N^{-1/3}$ (almost, in the non-squared case), assuming that the initial distribution of the limit nonlinear equation has finite moments of sufficiently high order ($4+\epsilon$ is enough when using the 2-Wasserstein distance). The proof relies on a convenient parametrization of the collision recently introduced by Hauray, as well as on a coupling technique developed by Cortez and Fontbona.