The structure of GCR and CCR groupoid C*-algebras

Author: van Wyk, Daniel Willem

Date: 2017

Publisher: University of Otago

Type: Thesis

Link to this item using this URL: http://hdl.handle.net/10523/7583

University of Otago

Abstract

We remove the assumptions of amenability in two theorems of Clark about C*-algebras of locally compact groupoids. The first result is that if the groupoid C*-algebra is GCR, or equivalently then the groupoid's orbits are locally closed. We prove the contrapositive. We begin by constructing a direct integral representation of the groupoid C*-algebra with respect to a measure on the groupoid's unit space. If the orbits are not locally closed, then there is a non-trivial ergodic measure on the unit space. We adapt a known result for transformation groups to groupoids, which shows that the direct integral representation cannot be type I if the measure on the unit space is non-trivially ergodic. The second result is that if the groupoid C*-algebra is CCR, then the groupoid's orbits are closed. Here we show that if a representation of a stability subgroup is induced to a representation of the groupoid C*-algebra, then the induced representation is equivalent to a representation as multiplication operators acting on a vector-valued L2-space. If we assume the groupoid C*-algebra is CCR, but an orbit is not closed, then the equivalence of two representations as multiplication operators leads to a contradiction.

Subjects: C*-algebras, Groupoids, Operator Algebras, GCR, CCR

Citation: ["van Wyk, D. W. (2017). The structure of GCR and CCR groupoid C*-algebras (Thesis, Doctor of Philosophy). University of Otago. Retrieved from http://hdl.handle.net/10523/7583"]

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