Tue, 07 Feb 2023
14:00
L6

Bornological and condensed mathematics

Federico Bambozzi
(University of Padova)
Abstract

I will explain how bornological and condensed structures can both be described as algebraic theories. I will also show how this permits the construction of functors between bornological and condensed structures. If time permits I will also briefly describe how to compare condensed derived geometry and bornological derived geometry and sketch how they relate to analytic geometry and Arakelov geometry

Tue, 31 Jan 2023
14:00
L6

Blocks for classical p-adic groups and the local Langlands correspondence

Robert Kurinczuk
((University of Sheffield))
Abstract

The local Langlands conjectures connect representations of p-adic groups to certain representations of Galois groups of local fields called Langlands parameters.  Recently, there has been a shift towards studying representations over more general coefficient rings and towards certain categorical enhancements of the original conjectures.  In this talk, we will focus on representations over coefficient rings with p invertible and how the corresponding category of representations of the p-adic group decomposes.  

Tue, 24 Jan 2023
14:00
L6

Highest weight theory and wall-crossing functors for reduced enveloping algebras

Matthew Westaway
(University of Birmingham)
Abstract

In the last few years, major advances have been made in our understanding of the representation theory of reductive algebraic groups over algebraically closed fields of positive characteristic. Four key tools which are central to this progress are highest weight theory, reduction to the principal block, wall-crossing functors, and tilting modules. When considering instead the representation theory of the Lie algebras of these algebraic groups, more subtleties arise. If we look at those modules whose p-character is in so-called standard Levi form we are able to recover the four tools mentioned above, but they have been less well-studied in this setting. In this talk, we will explore the similarities and differences which arise when employing these tools for the Lie algebras rather than the algebraic groups. This research is funded by a research fellowship from the Royal Commission for the Exhibition of 1851.

Tue, 17 Jan 2023
14:00
L6

Local Langlands correspondence and (stable) Bernstein center

Ju-Lee Kim
(MIT)
Abstract

We discuss the Local Langlands correspondence in connection with the Bernstein center and the Stable Bernstein center. We also give an example of stable Bernstein center as a stable essentially compact invariant distribution.

Nonlinear independent component analysis for discrete-time and continuous-time signals
Schell, A Oberhauser, H Annals of Statistics volume 51 issue 2 487-518 (13 Jun 2023)
Wed, 08 Mar 2023
16:00
L6

99 problems and presentations are most of them

Naomi Andrew
(University of Oxford)
Abstract

Geometric (even combinatorial) group theory suffers from the unfortunate situation that many obvious questions about group presentations (ex: is this a presentation of the trivial group? is this word the identity in that group?) cannot be answered. Not only "we don't know how to tell" but "we know that we cannot know how to tell" - this is called undecidability. This talk will serve as an introduction (for non-experts, since I am also such) to the area of group theoretic decision problems: I'll aim to cover some problems, some solutions (or half-solutions) and some of the general sources of undecidability, as well as featuring some of my (least?) favourite pathological groups.

Wed, 01 Mar 2023
16:00
L6

Algorithms and 3-manifolds

Adele Jackson
(University of Oxford)
Abstract

Given a mathematical object, what can you compute about it? In some settings, you cannot say very much. Given an arbitrary group presentation, for example, there is no procedure to decide whether the group is trivial. In 3-manifolds, however, algorithms are a fruitful and active area of study (and some of them are even implementable!). One of the main tools in this area is normal surface theory, which allows us to describe interesting surfaces in a 3-manifold with respect to an arbitrary triangulation. I will discuss some results in this area, particularly around Seifert fibered spaces.

Wed, 22 Feb 2023
16:00
L6

Stable commutator length in free and surface groups

Alexis Marchand
(University of Cambridge)
Abstract

Stable commutator length (scl) is a measure of homological complexity in groups that has attracted attention for its various connections with geometric topology and group theory. In this talk, I will introduce scl and discuss the (hard) problem of computing scl in surface groups. I will present some results concerning isometric embeddings of free groups for scl, and how they generalise to surface groups for the relative Gromov seminorm.

Wed, 15 Feb 2023
16:00
L6

[Cancelled]

Filippo Baroni
(University of Oxford)
Wed, 08 Feb 2023
16:00
L6

Minimal disks and the tower construction in 3-manifolds

Ognjen Tosic
(University of Oxford)
Abstract

A fundamental result in 3-manifold topology is the loop theorem: Given a null-homotopic simple closed curve in the boundary of a compact 3-manifold $M$, it bounds an embedded disk in $M$. The standard topological proof of this uses the tower construction due to Papakyriakopoulos. In this talk, I will introduce basic existence and regularity results on minimal surfaces, and show how to use the tower construction to prove a geometric version of the loop theorem due to Meeks--Yau: Given a null-homotopic simple closed curve in the boundary of a compact Riemannian 3-manifold $M$ with convex boundary, it bounds an embedded disk of least area. This also gives an independent proof of the (topological) loop theorem.

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