# Events for 02/21/2024 from all calendars

## Numerical Analysis Seminar

**Time: ** 3:00PM - 4:00PM

**Location: ** BLOC 302

**Speaker: **Harbir Antil, George Mason University

**Title: ***TBA*

**Abstract: **TBA

## Groups and Dynamics Seminar

**Time: ** 3:00PM - 4:00PM

**Location: ** BLOC 123

**Speaker: **Alain Valette, University of Neuchâtel

**Title: ***Maximal Haagerup subgroups in Z ^{n} x SL_{2}(Z)*

**Abstract: **The Haagerup property is a strong negation of Kazhdan's property (T). In a countable group, every Haagerup subgroup is contained in a maximal one. We propose to classify maximal Haagerup subgroups in the semi-direct product G_{n}=Z^{n} x SL_{2}(Z), where the action of SL_{2}(Z) on Z^{n} is induced by the unique irreducible representation of SL_{2}(R) on R^{n} (with n>1). We prove that there is a dichotomy for maximal Haagerup subgroups in G_{n}: either (amenable case) they are of the form Z^{n} x K, with K maximal amenable in SL_{2}(Z); or (non-amenable case) they are transverse to Z^{n}. This extends work by Jiang and Skalski for n=2. In joint work with P. Jolissaint, for n even, we prove the stronger result that the von Neumann algebra of Z^{n} x K (K as above) is maximal Haagerup in the von Neumann algebra of G_{n}. This involves looking at the orbit equivalence relation induced by SL_{2}(Z) on the n-torus, and proving that it satisfies a dichotomy: every ergodic sub-equivalence relation is either rigid or hyperfinite. This extends a result by Ioana for n=2.

## Student/Postdoc Working Geometry Seminar

**Time: ** 9:00PM - 10:10PM

**Location: ** BLOC 628

**Speaker: **Derek Wu, TAMU

**Title: ***Boij-Soederberg II*