Crossed Product $C^*$-algebras of Minimal Dynamical Systems on the Product of the Cantor Set and the Torus

TL;DR

This paper investigates the structure and classification of crossed product $C^*$-algebras arising from minimal dynamical systems on the product of the Cantor set and the torus, establishing conditions for their tracial rank and conjugacy relations.

Contribution

It demonstrates that for rotation cocycles, the associated crossed product $C^*$-algebras have tracial rank at most one, and under rigidity, they have rank zero, enabling classification via $K$-theory.

Findings

Tracial rank of these $C^*$-algebras is at most one for rotation cocycles.

Under rigidity, the $C^*$-algebras have tracial rank zero.

Isomorphisms in $K$-theory imply approximate $K$-conjugacy of the systems.

Abstract

This paper studies the relationship between minimal dynamical systems on the product of the Cantor set ($X$) and torus ($\T^2$) and their corresponding crossed product $C^*$-algebras. For the case when the cocycles are rotations, we studied the structure of the crossed product $C^*$-algebra $A$ by looking at a large subalgebra $A_x$. It is proved that, as long as the cocycles are rotations, the tracial rank of the crossed product $C^*$-algebra is always no more than one, which then indicates that it falls into the category of classifiable $C^*$-algebras. If a certain rigidity condition is satisfied, it is shown that the crossed product $C^*$-algebra has tracial rank zero. Under this assumption, it is proved that for two such dynamical systems, if $A$ and $B$ are the corresponding crossed product $C^*$-algebras, and we have an isomorphism between $K_i(A)$ and $K_i(B)$ which maps $K_i(C(X \times \T^2))$ to $K_i(C(X \times \T^2))$, then these two dynamical systems are approximately $K$-conjugate. The proof also indicates that $C^*$-strongly flip conjugacy implies approximate $K$-conjugacy in this case.