Department of Mathematics

Search

Geometry seminar

×

Modal title

Modal content

Please subscribe here if you would you like to be notified about these events via e-mail. Moreover you can also subscribe to the iCal/ics Calender.

Autumn Semester 2021

Date / Time Speaker Title Location
6 October 2021
15:45-16:45 		Dr. Danica Kosanović
ETH Zurich, Switzerland
Details

Geometry Seminar

Title Light bulbs in 4-manifolds
Speaker, Affiliation Dr. Danica Kosanović, ETH Zurich, Switzerland
Date, Time 6 October 2021, 15:45-16:45
Location HG G 43
Abstract Knowing when you can embed a surface into a 4-manifold is of fundamental importance for understanding the topology of that manifold. This brave new knot theory is even harder than the classical knot theory, but in certain situations, like in the setting when your embedded surfaces have a common "light bulb", one can completely classify all of them up to isotopy. I will explain how one can use techniques from homotopy theory to do this, resulting in some surprising applications of higher homotopy groups of embedding spaces. This is joint work with Peter Teichner.
Light bulbs in 4-manifoldsread_more
HG G 43
20 October 2021
15:45-16:45 		Giles Gardam
WWU Münster
Details

Geometry Seminar

Title Kaplansky's conjectures
Speaker, Affiliation Giles Gardam, WWU Münster
Date, Time 20 October 2021, 15:45-16:45
Location HG G 43
Abstract Three conjectures on group rings of torsion-free groups are commonly attributed to Kaplansky, namely the unit, zero divisor and idempotent conjectures. For example, the zero divisor conjecture predicts that if K is a field and G is a torsion-free group, then the group ring K[G] has no zero divisors. I will discuss these conjectures and their relationship to other conjectures and properties of groups. I will then explain how modern solvers for Boolean satisfiability can be applied to them, producing the first counterexample to the unit conjecture.
Kaplansky's conjecturesread_more
HG G 43
27 October 2021
15:45-16:45 		Arnaud Maret
Universität Heidelberg
Details

Geometry Seminar

Title Remarkable surface group representations in genus zero
Speaker, Affiliation Arnaud Maret, Universität Heidelberg
Date, Time 27 October 2021, 15:45-16:45
Location HG G 43
Abstract This talk is about a very special kind of representations of the fundamental group of a punctured sphere into PSL(2,R), discovered by Deroin and Tholozan. These representations have the key property of being totally elliptic. We will talk about the topology of their moduli space which turns out to be compact. I will explain how to parametrize them with chains of triangles in the upper half-plane and how to extract action-angle coordinates from that polygonal model.
Remarkable surface group representations in genus zeroread_more
HG G 43
3 November 2021
15:45-16:45 		Nicolas Monod
EPF Lausanne
Details

Geometry Seminar

Title Gelfand pairs and Iwasawa decompositions
Speaker, Affiliation Nicolas Monod, EPF Lausanne
Date, Time 3 November 2021, 15:45-16:45
Location HG G 43
Abstract I will prove that every Gelfand pair admits an Iwasawa decomposition. Before that, I will explain what Gelfand pairs are and why Iwasawa decompositions are useful.
Gelfand pairs and Iwasawa decompositionsread_more
HG G 43
10 November 2021
15:45-16:45 		Gabriel Pallier
Sorbonne Université, France
Details

Geometry Seminar

Title Invariants for sublinear bilipschitz equivalence
Speaker, Affiliation Gabriel Pallier, Sorbonne Université, France
Date, Time 10 November 2021, 15:45-16:45
Location HG G 43
Abstract Sublinear bilipschitz equivalences between metric spaces are generalized quasiisometries. In this generalization, the large-scale Lipschitz behavior is kept, while the (uniformly) coarse behavior is not. These equivalences appear in the study of asymptotic cones of Lie groups by Cornulier. They occur especially between families of non-pairwise quasiisometric nilpotent or solvable connected Lie groups. In this talk, I will give an introduction to sublinear bilipschitz equivalences and report on my work on revisiting the classical quasiisometry invariants of groups to determine which of them can be turned into invariants for sublinear bilipschitz equivalence. This lies in continuation of Gromov's questions of classifying homogeneous spaces (e.g. Riemannian symmetric spaces and noncompact solvmanifolds) up to quasiisometry and investigating their quasiisometric rigidity. Finally I will present a classification result for a small family of solvable Lie groups, and discuss the partially unsolved problems of rigidity in rank one (in the appropriate sense) and classification in higher rank.
Invariants for sublinear bilipschitz equivalenceread_more
HG G 43
24 November 2021
15:45-16:45 		Hugo Parlier
University of Luxembourg
Details

Geometry Seminar

Title Where the orthogeodesics roam
Speaker, Affiliation Hugo Parlier, University of Luxembourg
Date, Time 24 November 2021, 15:45-16:45
Location HG G 43
Abstract The lengths of geodesics on hyperbolic surfaces satisfy intriguing equations, known as identities, relating these lengths to geometric quantities of the surface. The talk will be about a family of identities that relate lengths of closed geodesics and orthogeodesics to boundary lengths. This family includes identities due to Basmajian, McShane, Mirzakhani and Tan-Wong-Zhang as particular cases.
Where the orthogeodesics roamread_more
HG G 43

Archive: AS 24 SS 24 AS 23 SS 23 AS 22 SS 22 AS 21 AS 20 SS 20 AS 19 SS 19 AS 18 SS 18 AS 17 SS 17 AS 16 SS 16 AS 15 SS 15 AS 14 SS 14 AS 13 SS 13 AS 12 SS 12 AS 11 SS 11 AS 10 SS 10 AS 09 SS 09

JavaScript has been disabled in your browser