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On Kumjian's C*-diagonals and the opaque ideal

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arxiv 2110.09445 v2 pith:DK7F5JGZ submitted 2021-10-18 math.OA

classification math.OA
keywords abelianidealopaquealgebrasdiagonalsextensionkumjianproperty
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abstract

We characterize exotic C*-algebras of twisted, principal \'etale groupoids, together with the abelian subalgebra associated to the unit space, as precisely being the inclusions "$A\subseteq B$" of C*-algebras in which $A$ is abelian, regular, and satisfies the extension property (pure states extend uniquely to $B$). When $B$ is moreover nuclear, we deduce that the corresponding opaque ideal is trivial. As an application, we give a streamlined characterization of Kumjian's C*-diagonals as the regular abelian subalgebras satisfying the extension property with vanishing opaque ideal.

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Cited by 2 Pith papers

Reviewed papers in the Pith corpus that reference this work. Sorted by Pith novelty score. Full citation record

  1. A C*-diagonal in the Jiang-Su algebra via entangled matrix cones

    math.OA 2026-07 accept novelty 7.0 of 10

    An explicit inductive system of entangled dimension-drop algebras realises Z and yields a C*-diagonal with one-dimensional non-locally-connected spectrum, via a new normaliser characterisation by state excision.

  2. Pseudo-Cartan Inclusions

    math.OA 2025-02 conditional novelty 7.0 of 10

    For regular inclusions with abelian subalgebra, having a Cartan envelope is equivalent to having a faithful unique pseudo-expectation, now proven without the unital hypothesis.

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