• Corpus ID: 235765413

The ideal intersection property for essential groupoid C*-algebras

@inproceedings{Kennedy2021TheII,
  title={The ideal intersection property for essential groupoid C*-algebras},
  author={Matthew Kennedy and Se-Jin Kim and Xin Li and Sven Raum and Dan Ursu},
  year={2021}
}

• M. Kennedy, Se-Jin Kim, +2 authors D. Ursu
• Published 8 July 2021
• Mathematics

We characterise, in several complementary ways, étale groupoids with locally compact Hausdorff space of units whose essential groupoid C∗-algebra has the ideal intersection property, assuming that the groupoid is either Hausdorff or σ-compact. This leads directly to a characterisation of the simplicity of this C∗-algebra which, for Hausdorff groupoids, agrees with the reduced groupoid C∗-algebra. Specifically, we prove that the ideal intersection property is equivalent to the absence of essentially confined amenable sections of isotropy groups. For groupoids with compact space of units we moreover show that this is equivalent to the uniqueness of equivariant pseudoexpectations. A key technical idea underlying our results is a new notion of groupoid action on C∗-algebras including the essential groupoid C∗-algebra itself. For minimal groupoids, we further obtain a relative version of Powers averaging property. Examples arise from suitable group representations into simple groupoid C∗-algebras. This is illustrated by the example of the quasi-regular representation of Thompson’s group T with respect to Thompson’s group F, which satisfies the relative Powers averaging property in the Cuntz algebraO2.