Entropy production inequalities for the Kac Walk

TL;DR

This paper establishes new entropy production inequalities for the Kac Walk and demonstrates how these results support Kac's program of deriving properties of the Boltzmann equation from the walk, partially addressing the Cercignani Conjecture.

Contribution

It introduces novel entropy production inequalities for the Kac Walk and a new form of chaoticity, linking these to entropy inequalities for the Boltzmann equation.

Findings

Entropy production inequalities for the Kac Walk are established.

These inequalities imply entropy production results for the Boltzmann equation.

Partial progress on the 'Almost' Cercignani Conjecture on the sphere.

Abstract

Mark Kac introduced what is now called 'the Kac Walk' with the aim of investigating the spatially homogeneous Boltzmann equation by probabilistic means. Much recent work, discussed below, on Kac's program has run in the other direction: using recent results on the Boltzmann equation, or its one-dimensional analog, the non-linear Kac-Boltzmann equation, to prove results for the Kac Walk. Here we investigate new functional inequalities for the Kac Walk pertaining to entropy production, and introduce a new form of `chaoticity'. We then show how these entropy production inequalities imply entropy production inequalities for the Kac-Boltzmann equation. This results validate Kac's program for proving results on the non-linear Boltzmann equation via analysis of the Kac Walk, and they constitute a partial solution to the `Almost' Cercignani Conjecture on the sphere.