Wed, 12 Jun 2013

16:00 - 17:00
SR1

Ascending HNN extensions and the BNS invariant

Benno Kuckuck
(University of Oxford)
Abstract

 To any splitting of a group G as an HNN extension we can associate a map from G to Z. Conversely, a group that allows a non-trivial homomorphism to Z may be written as an HNN extension in an obvious way. In this talk we will consider the question when such a homomorphism G->Z is associated to a non-obvious HNN splitting of G. We will then see how this information can be collected into an invariant of the group which may be described by a simple connectivity condition on Cayley graphs.
Wed, 05 Jun 2013

15:30 - 16:30
SR1

Boundaries of Random Walks

Elisabeth Fink
(University of Oxford)
Abstract

I will talk about random walks on groups and define the Poisson boundary of such. Studying it gives criteria for amenability or growth. I will outline how this can be used and describe recent related results and still open questions.

Wed, 29 May 2013

16:00 - 17:00
SR1

Group von Neumann algebras of locally compact HNN-extensions

Sven Raum
(KU Leuven)
Abstract

This talk consists of three parts. As a motivation, we are first going to introduce von Neumann algebras associated with discrete groups and briefly describe their interplay with measurable group theory. Next, we are going to consider group von Neumann algebras of general locally compact groups and highlight crucial differences between the discrete and the non-discrete case. Finally, we present some recent results on group von Neumann algebras associated with certain locally compact HNN-extensions.

Tue, 11 Jun 2013

14:00 - 15:00
SR1

Bridgeland 40 conference: $E_n$-deformations and quantizations of derived stacks I

Chris Brav
(Oxford)
Abstract

We review the theory of $E_n$-algebras (roughly, algebras with $n$ compatible multiplications) and discuss $E_n$-deformation theory in

the sense of Lurie. We then describe, to the best of our ability, the use of $E_n$-deformation theory in the on-going work of Calaque, Pantev, Toen,

Vezzosi, and Vaquie about deformation quantization of derived stacks with shifted Poisson structure.

Mon, 22 Apr 2013

16:00 - 17:00
SR1

The eigencurve

Jan Vonk
(Oxford)
Mon, 04 Mar 2013

16:00 - 17:00
SR1

A primer on Burgess bounds

Lillian Pierce
(Oxford)
Abstract

We'll present a proof of the basic Burgess bound for short character sums, following the simplified presentation of Gallagher and Montgomery.

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