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Analysis SeminarExport this event to calendar

Wednesday, November 27, 2019 — 3:30 PM EST

Dan Ursu, Department of Pure Mathematics, University of Waterloo

"Relative C* - simplicity"

Given a group G acting on a C*-algebra A, the reduced crossed product is a C*-algebra containing a copy of G (as unitaries) and A, where the action of G on A is now inner. A recent result of Amrutam gives a sufficient condition for all C*-subalgebras of a crossed product that contain G to also themselves be crossed products with G. Namely, this is true if the kernel of the action of G on A is what he calls plump.

Plumpness is a relative version of something called Powers's averaging property, which is known to be equivalent to the reduced C*-algebra of G being simple (i.e. G is C*-simple). With this in mind, we come up with the notion of a relatively C*-simple subgroup, and show that these two notions are equivalent for normal subgroups, along with several other characterizations. In this talk, I will give an overview of these equivalences, and then use them to give various examples of relatively C*-simple subgroups.

MC 5417

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