Classifiable $\mathrm{C}^*$-algebras from minimal $\mathbb{Z}$-actions and their orbit-breaking subalgebras

TL;DR

This paper characterizes the K-theory of C*-algebras from minimal dynamical systems, showing they can realize a wide range of invariants and advancing the classification program for these algebras.

Contribution

It provides a complete characterization of K-theory for C*-algebras from minimal Z-actions and constructs orbit-breaking algebras with prescribed invariants, enhancing classification results.

Findings

Crossed products by minimal homeomorphisms realize all finitely generated K-theories.

Orbit-breaking algebras can be constructed with arbitrary countable abelian K-groups and specified tracial state spaces.

Results advance the Elliott classification program for C*-algebras from étale equivalence relations.

Abstract

In this paper we consider the question of what abelian groups can arise as the $K$-theory of $\mathrm{C}^*$-algebras arising from minimal dynamical systems. We completely characterize the $K$-theory of the crossed product of a space $X$ with finitely generated $K$-theory by an action of the integers and show that crossed products by a minimal homeomorphisms exhaust the range of these possible $K$-theories. Moreover, we may arrange that the minimal systems involved are uniquely ergodic, so that their $\mathrm{C}^*$-algebras are classified by their Elliott invariants. We also investigate the $K$-theory and the Elliott invariants of orbit-breaking algebras. We show that given arbitrary countable abelian groups $G_0$ and $G_1$ and any Choquet simplex $\Delta$ with finitely many extreme points, we can find a minimal orbit-breaking relation such that the associated $\mathrm{C}^*$-algebra has $K$-theory given by this pair of groups and tracial state space affinely homeomorphic to $\Delta$. We also improve on the second author's previous results by using our orbit-breaking construction to $\mathrm{C}^*$-algebras of minimal amenable equivalence relations with real rank zero that allow torsion in both $K_0$ and $K_1$. These results have important applications to the Elliott classification program for $\mathrm{C}^*$-algebras. In particular, we make a step towards determining the range of the Elliott invariant of the $\mathrm{C}^*$-algebras associated to \'{e}tale equivalence relations.