# Invariant measures for the box-ball system based on stationary Markov chains and periodic Gibbs measures

## TL;DR

This paper surveys invariant measures for the box-ball system, introduces new Gibbs measure-based measures for periodic configurations, and discusses scaling limits and connections to zigzag processes and Toda lattices.

## Contribution

It extends previous work by introducing Gibbs measure-based invariant measures for periodic configurations and explores new scaling limits and connections to other stochastic processes.

## Key findings

- Invariant measures for BBS include stationary Markov chain-based and Gibbs measure-based families.
- Infinite volume limits of Gibbs measures recover earlier Markov chain measures.
- New scaling limits, including a novel periodic zigzag process, are identified.

## Abstract

The box-ball system (BBS) is a simple model of soliton interaction introduced by Takahashi and Satsuma in the 1990s. Recent work of the authors, together with Tsuyoshi Kato and Satoshi Tsujimoto, derived various families of invariant measures for the BBS based on two-sided stationary Markov chains. In this article, we survey the invariant measures that were presented in the latter work, and also introduce a family of new ones for periodic configurations that are expressed in terms of Gibbs measures. Moreover, we show that the former examples can be obtained as infinite volume limits of the latter. Another aspect of the previous work was to describe scaling limits for the box-ball system; here, we review these results, and also present scaling limits other than those that were covered there. One, the zigzag process has previously been observed in the context of queuing; another, a periodic version of the zigzag process, is apparently novel. Furthermore, we demonstrate that certain Palm measures associated with the stationary and periodic versions of the zigzag process yield natural invariant measures for the dynamics of corresponding versions of the ultra-discrete Toda lattice.