Multitime fields and hard rod scaling limits

TL;DR

This paper studies multitime fields generated by Poisson line processes and their scaling limits, linking them to Gaussian fields, and explores the hydrodynamic behavior of hard rods, including ideal gas dynamics.

Contribution

It introduces a novel connection between Poisson line processes, multitime fields, and hard rod dynamics, providing new hydrodynamic limit results.

Findings

Multitime walk fields converge to multitime Brownian motion under diffusive scaling.

Hard rod systems exhibit Euler and diffusive hydrodynamic limits.

Zero rod size case relates to ideal gas dynamics and invariant measures.

Abstract

A Poisson line process is a random set of straight lines contained in the plane, as the image of the map $(x,v)\mapsto (x+vt)_{t\in\mathbb{R}}$, for each point $(x,v)$ of a Poisson process in the space-velocity plane. By associating a step with each line of the process, a random surface called multitime walk field is obtained. The diffusive rescaling of the surface converges to the multitime Brownian motion, a classical Gaussian field also called L\'evy-Chentsov field. A cut of the multitime fields with a perpendicular plane, reveals a one dimensional continuous time random walk and a Brownian motion, respectively. A hard rod is an interval contained in $\mathbb{R}$ that travels ballistically until it collides with another hard rod, at which point they interchange positions. By associating each line with the ballistic displacement of a hard rod and associating surface steps with hard rod jumps, we obtain the hydrodynamic limits of the hard rods in the Euler and diffusive scalings. The main tools are law of large numbers and central limit theorems for Poisson processes. When rod sizes are zero we have an ideal gas dynamics. We describe the relation between ideal gas and hard-rod invariant measures.