Lifting KK-elements, asymptotical unitary equivalence and classification of simple C*-algebras

TL;DR

This paper develops methods to lift KK-elements to monomorphisms between simple unital C*-algebras with tracial rank zero, advancing classification by connecting K-theory, traces, and asymptotic unitary equivalence.

Contribution

It introduces new techniques for realizing KK-elements as monomorphisms and extends classification results for simple C*-algebras using trace and K-theory data.

Findings

Existence of monomorphisms realizing KK-elements with specified trace behavior

Construction of monomorphisms with prescribed rotation maps

Applications to the classification of simple C*-algebras

Abstract

Let $A$ and $C$ be two unital simple C*-algebas with tracial rank zero. Suppose that $C$ is amenable and satisfies the Universal Coefficient Theorem. Denote by ${{KK}}_e(C,A)^{++}$ the set of those $\kappa$ for which $\kappa(K_0(C)_+\setminus\{0\})\subset K_0(A)_+\setminus\{0\}$ and $\kappa([1_C])=[1_A]$. Suppose that $\kappa\in {KK}_e(C,A)^{++}.$ We show that there is a unital monomorphism $\phi: C\to A$ such that $[\phi]=\kappa.$ Suppose that $C$ is a unital AH-algebra and $\lambda: \mathrm{T}(A)\to \mathrm{T}_{\mathtt{f}}(C)$ is a continuous affine map for which $\tau(\kappa([p]))=\lambda(\tau)(p)$ for all projections $p$ in all matrix algebras of $C$ and any $\tau\in \mathrm{T}(A),$ where $\mathrm{T}(A)$ is the simplex of tracial states of $A$ and $\mathrm{T}_{\mathtt{f}}(C)$ is the convex set of faithful tracial states of $C.$ We prove that there is a unital monomorphism $\phi: C\to A$ such that $\phi$ induces both $\kappa$ and $\lambda.$ Suppose that $h: C\to A$ is a unital monomorphism and $\gamma \in \mathrm{Hom}(\Kone(C), \aff(A)).$ We show that there exists a unital monomorphism $\phi: C\to A$ such that $[\phi]=[h]$ in ${KK}(C,A),$ $\tau\circ \phi=\tau\circ h$ for all tracial states $\tau$ and the associated rotation map can be given by $\gamma.$ Applications to classification of simple C*-algebras are also given.