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Zbl 1116.46057
Fang, Xiaochun
The real rank zero property of crossed product.
(English)
[J] Proc. Am. Math. Soc. 134, No. 10, 3015-3024 (2006). ISSN 0002-9939; ISSN 1088-6826/e

Let $(A,G,\alpha)$ be a $C^*$-dynamical system with $A$ a unital $C^*$-algebra and $G$ a discrete Abelian group. The paper under review studies the canonical continuous affine restriction map $R$ from the trace state space of the crossed product $A\rtimes_\alpha G$ to the space $T(A)_{\alpha^*}$ of $\alpha$-invariant trace states on $A$. The following results are proven: \par (1) If $\widehat{G}$ is connected and $A\rtimes_\alpha G$ has real rank zero, then $R$ is an affine homeomorphism with inverse $\Phi$ given by $\Phi (\tau)=\tau\circ \phi$, $\tau\in T(A)_{\alpha^*}$, where $\phi$ denotes the canonical conditional expectation from $A\rtimes_\alpha G$ onto $A$. \par (2) If $R$ is a homeomorphism, then $A\rtimes_\alpha G$ has real rank zero iff all products between unitaries in $U_0(A)$ and in the commutator subgroup generated by $C_c (G,A)\cap U_0(A\rtimes_\alpha G)$ can be approximated in $A\rtimes_\alpha G$ by unitaries with finite spectrum. This result is further strengthened when $A$ is an inductive limit of non-elementary" simple $C^*$-algebras of real rank zero. Important technical tools in the proofs are provided by the determinant associated to a trace by {\sl P.\,de~la Harpe} and {\it G.\,Skandalis} [Ann.\ Inst.\ Fourier 34, No.\,1, 241--260 (1984; Zbl 0521.46037)] and by a theorem of {\it K.\,Thomsen} [Publ.\ Res.\ Inst.\ Math.\ Sci.\ 31, No.\,6, 1011--1029 (1995; Zbl 0853.46037)] .
[Florin P. Boca (Urbana-Champaign)]
MSC 2000:
*46L55 Noncommutative dynamical systems
46L05 General theory of C*-algebras
46L35 Classifications and factors of C*-algebras
46L40 Automorphisms of C*-algebras

Keywords: trace state space; crossed product; real rank zero

Citations: Zbl 0521.46037; Zbl 0853.46073; Zbl 0853.46037

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