Supports of ideals in reduced groupoid C*-algebras and applications

Kang Li 李康  (Friedrich-Alexander-Universitat Erlangen-Nürnberg, Germany)

14:30-15:30, September 5, 2025   SIMIS 1410

Abstract:

In joint work with Jiawen Zhang, we study ideals in reduced C*-algebras of general étale groupoids.Each ideal I naturally gives rise to two open invariant subsets of G", the inner support U] and outer support V. By introducing the notion of ghostly ideals, we extend the sandwiching result from inner exact groupoids to the general case, and use effectiveness together with the intersection property to characterise when the inner and outer supports coincide. We also present applications to regular ideals, tracial ideals, and the amenability problem for Thompson's group F.

About the speaker:

Kang Li is a Danish mathematician specializing in operator algebras and their applications to dynamical systems, geometric group theory, and representation theory. He has published over 30 papers in leading journals, including IMRN, Journal of Functional Analysis, Advances in Mathematics, and Ergodic Theory and Dynamical Systems. His research interests closely align with those of Fudan University and East China Normal University, with which he has maintained extensive collaborations.

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