On dense subalgebras of the singular ideal in groupoid C*-algebras

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Hauptverfasser: Gonzales, Julian, Hume, Jeremy B.
Format: Preprint
Veröffentlicht: 2025
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author Gonzales, Julian
Hume, Jeremy B.
author_facet Gonzales, Julian
Hume, Jeremy B.
contents We prove that ideals in amenable second-countable non-Hausdorff étale groupoid $C^*$-algebras are determined by their isotropy fibres. As an application, we characterise when the singular functions in Connes' algebra are dense in the singular ideal in terms of a property of explicit ideals in the isotropy group $C^*$-algebras. We then show this density property holds for all $C^*$-algebras of groupoids with finite-by-nilpotent isotropy groups.
format Preprint
id arxiv_https___arxiv_org_abs_2511_04391
institution arXiv
publishDate 2025
record_format arxiv
spellingShingle On dense subalgebras of the singular ideal in groupoid C*-algebras
Gonzales, Julian
Hume, Jeremy B.
Operator Algebras
22A22, 46L05 (Primary), 37A55, 22D25 (Secondary)
We prove that ideals in amenable second-countable non-Hausdorff étale groupoid $C^*$-algebras are determined by their isotropy fibres. As an application, we characterise when the singular functions in Connes' algebra are dense in the singular ideal in terms of a property of explicit ideals in the isotropy group $C^*$-algebras. We then show this density property holds for all $C^*$-algebras of groupoids with finite-by-nilpotent isotropy groups.
title On dense subalgebras of the singular ideal in groupoid C*-algebras
topic Operator Algebras
22A22, 46L05 (Primary), 37A55, 22D25 (Secondary)
url https://arxiv.org/abs/2511.04391