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Our seminar runs on Tuesdays from 13:00 to 14:00. Contact:
30/09/2025: David Jekel (Københavns Universitet), at 13:00 in U177.
Title: The unitary group of a II_1 factor is SOT-contractible
Abstract: I show that the unitary group of any SOT-separable II_1 factor M, with the strong operator topology, is contractible. Combined with several old results, this implies that the same is true for any SOT-separable von Neumann algebra with no type I_n direct summands (n < infinity). The proof for the II_1-factor case uses regularization via free convolution and Popa's theorem on the existence of approximately free Haar unitaries in II_1 factors. I will also explain some of the bigger picture of the free probability ingredients.
07/10/2025: Jamie Bell (University of Münster), at 13:00 in U166.
Title: Stable rank one in nonnuclear crossed products
Abstract: I’ll give an overview of stable rank one and the C*-algebras known to have it, then describe a new approach to studying stable rank one in possibly nonnuclear crossed products. As an application, we show that stable rank one is generic for natural classes of minimal actions of free groups on the Cantor set. This is joint work with Shirly Geffen and David Kerr.
14/10/2025: No seminar due to Autumn Break
21/10/2025: TBA, at 13:00 in U163.
Title: TBA
Abstract: TBA
28/10/2025: Prem Nigam Kar (Technical University of Denmark), at 13:00 in U183.
Title: Computing Quantum Automorphism Groups of Graphs
Abstract: The quantum automorphism group of a graph is a natural generalization of the notion of automorphism group of a graph in the framework of compact quantum groups. What makes these objects particularly interesting is their interplay with the Graph Isomorphism nonlocal game from quantum information theory. However, explicit computation of quantum automorphism groups of graphs is quite difficult and few general results were known a few years ago. In this talk, we shall explore algebraic and combinatorial tools which enable us to compute quantum automorphism groups of larger graphs from those of simpler ones. In particular, we give explicit algorithms for computing quantum automorphism groups of large families of graphs such as forests, outerplanar graphs, and block graphs, and study quantum automorphism groups of lexicographic products of graphs.
04/11/2025: Jens Kaad (SDU), at 13:00 in U166.
Title: TBA
Abstract: TBA
11/11/2025: TBA, at 13:00 in U163.
Title: TBA
Abstract: TBA
18/11/2025: Rufus Willett (University of Hawai'i at Mānoa), at 13:00 in U168.
Title: TBA
Abstract: TBA
25/11/2025: TBA, at 13:00 in U168.
Title: TBA
Abstract: TBA
2/12/2025: TBA, at 13:00 in U168.
Title: TBA
Abstract: TBA
5/12/2025 (Friday): Arnaud Brothier (University of Trieste), at 10:00 in U173.
Title: TBA
Abstract: TBA
9/12/2025: Andrew Toms (Purdue University), at 13:00 in U164.
Title: TBA
Abstract: TBA
16/12/2025: TBA, at 13:00 in U164.
Title: TBA
Abstract: TBA
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