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Spring Semester 2025

Date / Time Speaker Title Location
19 March 2025
15:30-16:30 		Raphael Appenzeller
Universität Heidelberg
Details

Geometry Seminar

Title Characterizing hyperbolicity via game theory
Speaker, Affiliation Raphael Appenzeller, Universität Heidelberg
Date, Time 19 March 2025, 15:30-16:30
Location HG G 43
Abstract The cop numbers are two new integer-valued invariants of finitely generated groups defined in terms of a two player pursuit game played on Cayley graphs. We use the cop numbers to give a new characterization of hyperbolic groups and virtually free groups. We discuss potential applications and recent progress on remaining open questions. This is joint work with Kevin Klinge.
Characterizing hyperbolicity via game theoryread_more
HG G 43
26 March 2025
15:30-16:30 		Yash Lodha
University of Hawaii at Manoa
Details

Geometry Seminar

Title Two new constructions of finitely presented infinite simple groups
Speaker, Affiliation Yash Lodha, University of Hawaii at Manoa
Date, Time 26 March 2025, 15:30-16:30
Location HG G 43
Abstract I will describe two new constructions of finitely presented infinite simple groups. First, I will present a construction of finitely presented (and type F∞) simple groups that act by orientation preserving homeomorphisms on the real line. These are the first such examples. Next, I will present a construction of a family of finitely presented infinite uniformly simple groups, where the Ulam width can get arbitrarily large. Among the class of finitely generated (but not finitely presentable) groups, the existence of such examples was demonstrated in the work of Ivanov from 1989. Our construction provides the first such family of examples in the class of infinite finitely presented groups. This is joint work with James Hyde.
Two new constructions of finitely presented infinite simple groupsread_more
HG G 43
2 April 2025
15:30-16:30 		Leonid Monin
EPFL
Details

Geometry Seminar

Title Geometry of matrix inversion
Speaker, Affiliation Leonid Monin, EPFL
Date, Time 2 April 2025, 15:30-16:30
Location HG G 43
Abstract In this talk I will explain how to invert matrices using an action of algebraic torus on certain algebraic varieties. Along the way, I will recall the construction of permutohedral toric variety and the space of complete quadrics, and explore the connection between them. As an application, I will present a recent polynomiality result for characteristic numbers of quadrics which was conjectured by Sturmfels and Uhler. Only very basic knowledge of algebraic geometry is needed.
Geometry of matrix inversionread_more
HG G 43
9 April 2025
15:30-16:30 		Anthony Genevois
Institut Montpellierain Alexander Grothendieck
Details

Geometry Seminar

Title Quasi-median graphs, right-angled Artin groups, and homotopy
Speaker, Affiliation Anthony Genevois, Institut Montpellierain Alexander Grothendieck
Date, Time 9 April 2025, 15:30-16:30
Location HG G 43
Abstract After a general introduction to applications of metric graph theory in geometric group theory, focused on quasi-median graphs, I will explain how one can deduce from such a perspective new quasi-isometric invariants for right-angled Artin groups. This is joint work with Carolyn Abbott and Eduardo Martinez-Pedrosa.
Quasi-median graphs, right-angled Artin groups, and homotopyread_more
HG G 43
16 April 2025
15:30-16:30 		Jeremy Tyson
University of Illinois Urbana-Champaign
Details

Geometry Seminar

Title Dimension interpolation and conformal dimension
Speaker, Affiliation Jeremy Tyson, University of Illinois Urbana-Champaign
Date, Time 16 April 2025, 15:30-16:30
Location HG G 43
Abstract The conformal dimension of a metric space $(X,d)$ measures its optimal shape from the perspective of quasiconformal geometry. It is defined by infimizing dimension over metrics in the quasisymmetric equivalence class of $d$. Introduced by Pierre Pansu in 1989, conformal Hausdorff dimension played an important early role in the development of analysis on metric spaces. Subsequently a variant notion, conformal Assouad dimension, gained prominence. Assouad dimension—which bounds Hausdorff dimension from above—is a scale-invariant, quantitative measurement of optimal coverings of a space. Dimension interpolation is an emerging program of research in fractal geometry which identifies geometrically natural one-parameter dimension functions interpolating between existing concepts. Two exemplars are the Assouad spectrum (Fraser-Yu, 2015), which interpolates between box-counting and Assouad dimension, and the intermediate dimensions (Falconer-Fraser-Kempton, 2020), which interpolate between Hausdorff and box-counting dimension. In this talk, I’ll discuss the mapping-theoretic properties of intermediate dimensions and the Assouad spectrum, with applications to the quasiconformal classification of sets and to the range of conformal Assouad spectrum. The latter results are based on a recent joint project with Efstathios Chrontsios Garitsis (Univ of Tennessee) and an ongoing collaboration with Jonathan Fraser (Univ of St. Andrews).
Dimension interpolation and conformal dimensionread_more
HG G 43
23 April 2025
15:30-16:30
Details

Geometry Seminar

Title Easter break
Speaker, Affiliation
Date, Time 23 April 2025, 15:30-16:30
Location
Easter break
30 April 2025
15:30-16:30 		Stephan Stadler
MPIM Bonn
Details

Geometry Seminar

Title Title T.B.A.
Speaker, Affiliation Stephan Stadler, MPIM Bonn
Date, Time 30 April 2025, 15:30-16:30
Location HG G 43
Title T.B.A.
HG G 43
7 May 2025
15:30-16:30 		Hugo Parlier
Université de Fribourg
Details

Geometry Seminar

Title Title T.B.A.
Speaker, Affiliation Hugo Parlier, Université de Fribourg
Date, Time 7 May 2025, 15:30-16:30
Location HG G 43
Title T.B.A.
HG G 43
14 May 2025
15:30-16:30 		Stefanie Zbinden
Heriot-Watt University
Details

Geometry Seminar

Title Title T.B.A.
Speaker, Affiliation Stefanie Zbinden, Heriot-Watt University
Date, Time 14 May 2025, 15:30-16:30
Location HG G 43
Title T.B.A.
HG G 43
21 May 2025
15:30-16:30 		Paula Truöl
MPIM Bonn
Details

Geometry Seminar

Title Title T.B.A.
Speaker, Affiliation Paula Truöl, MPIM Bonn
Date, Time 21 May 2025, 15:30-16:30
Location HG G 43
Title T.B.A.
HG G 43
28 May 2025
15:30-16:30 		Livio Liechti
Université de Fribourg
Details

Geometry Seminar

Title Title T.B.A.
Speaker, Affiliation Livio Liechti, Université de Fribourg
Date, Time 28 May 2025, 15:30-16:30
Location HG G 43
Title T.B.A.
HG G 43

Notes: the highlighted event marks the next occurring event.

Organisers: Manfred Einsiedler, Urs Lang, Lukas Lewark, Christian Urech

Archive: SS 25 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