Classification of homomorphisms and dynamical systems

Abstract

Let $A$ be a unital simple C*-algebra with tracial rank zero and $X$ be a compact metric space. Suppose that $h_1, h_2: C(X)\to A$ are two unital monomorphisms. We show that $h_1$ and $h_2$ are approximately unitarily equivalent if and only if $$ [h_1]=[h_2] {\rm in} KL(C(X),A) {\rm and} τ\circ h_1(f)=τ\circ h_2(f) $$ for every $f\in C(X)$ and every trace $τ$ of $A.$ Adopting a theorem of Tomiyama, we introduce a notion of approximate conjugacy for minimal dynamical systems. Let $X$ be a compact metric space and $α, β: X\to X$ be two minimal homeomorphisms. Using the above mentioned result, we show that two dynamical systems are approximately conjugate in that sense if and only if a $K$-theoretical condition is satisfied. In the case that $X$ is the Cantor set, this notion coincides with strong orbit equivalence of Giordano, Putnam and Skau and the $K$-theoretical condition is equivalent to saying that the associate crossed product C*-algebras are isomorphic. Another application of the above mentioned result is given for $C^*$-dynamical systems related to a problem of Kishimoto. Let $A$ be a unital simple AH-algebra with no dimension growth and with real rank zero, and let $α\in Aut(A).$ We prove that if $α^r$ fixes a large subgroup of $K_0(A)$ and has the tracial Rokhlin property then $A\rtimes_α\Z$ is again a unital simple AH-algebra with no dimension growth and with real rank zero.