Quotients of $\mathbb{N}^*$, $\omega$-limit sets, and chain transitivity

TL;DR

This paper characterizes which dynamical systems can be obtained as quotients of the space , showing they are exactly the -limit sets of points in larger systems, with additional results under set-theoretic assumptions.

Contribution

It provides a complete external characterization of quotients of  and, under certain set-theoretic assumptions, a partial internal characterization, especially for metrizable systems.

Findings

A dynamical system is a quotient of  iff it is an -limit set of some point.

Under MA_{}-centered, chain transitivity characterizes quotients of  for systems of weight .

Full internal characterization achieved for metrizable systems.

Abstract

$\mathbb{N}^* = \beta\mathbb{N} \setminus \mathbb{N}$ has a canonical dynamical structure provided by the shift map, the unique continuous extension to $\beta\mathbb{N}$ of the map $n \mapsto n+1$ on $\mathbb{N}$. Here we investigate the question of what dynamical systems can be written as quotients of $\mathbb{N}^*$. We prove that a dynamical system is a quotient of $\mathbb{N}^*$ if and only if it is isomorphic to the $\omega$-limit set of some point in some larger system. This provides a full external characterization of the quotients of $\mathbb{N}^*$. We also prove, assuming MA$_{\sigma\text{-centered}}(\kappa)$, that a dynamical system of weight $\kappa$ is a quotient of $\mathbb{N}^*$ if and only if it is chain transitive. This provides a consistent partial internal characterization of the quotients of $\mathbb{N}^*$, and a full internal characterization for metrizable systems.