Article contents
Dynamical systems of type
$(m,n)$ and their
$\mathrm {C}^*$-algebras
Published online by Cambridge University Press: 27 July 2012
Abstract
Given positive integers $n$ and
$m$, we consider dynamical systems in which (the disjoint union of)
$n$ copies of a topological space is homeomorphic to
$m$ copies of that same space. The universal such system is shown to arise naturally from the study of a C*-algebra denoted by
${\cal O}_{m,n}$, which in turn is obtained as a quotient of the well-known Leavitt C*-algebra
$L_{m,n}$, a process meant to transform the generating set of partial isometries of
$L_{m,n}$ into a tame set. Describing
${\cal O}_{m,n}$ as the crossed product of the universal
$(m,n)$-dynamical system by a partial action of the free group
$\mathbb {F}_{m+n}$, we show that
${\cal O}_{m,n}$ is not exact when
$n$ and
$m$ are both greater than or equal to 2, but the corresponding reduced crossed product, denoted by
${\cal O}_{m,n}^r$, is shown to be exact and non-nuclear. Still under the assumption that
$m,n\geq 2$, we prove that the partial action of
$\mathbb {F}_{m+n}$ is topologically free and that
${\cal O}_{m,n}^r$ satisfies property (SP) (small projections). We also show that
${\cal O}_{m,n}^r$admits no finite-dimensional representations. The techniques developed to treat this system include several new results pertaining to the theory of Fell bundles over discrete groups.
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- Research Article
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- Copyright
- Copyright © 2012 Cambridge University Press
References
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