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Autumn Semester 2026

Date / Time Speaker Title Location
16 September 2026
15:30-16:30
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Geometry Seminar

Title kein Seminar
Speaker, Affiliation
Date, Time 16 September 2026, 15:30-16:30
Location HG G 43
kein Seminar
HG G 43
23 September 2026
15:30-16:30 		Segev Gonen Cohen
ETH Zurich, Switzerland
Details

Geometry Seminar

Title Actions of lattices on manifolds
Speaker, Affiliation Segev Gonen Cohen, ETH Zurich, Switzerland
Date, Time 23 September 2026, 15:30-16:30
Location HG G 43
Abstract In this talk we describe recent progress on the Zimmer Programme, the study of actions of lattices in Lie groups on manifolds by diffeomorphisms. We begin by recalling motivations and some important examples, explain the general strategy introduced by Brown-Fisher-Hurtado when the manifold is of low enough dimension, and discuss modifications that allow us to prove results in more general semisimple and S-arithmetic groups. Time willing, we will also describe some recent progress on actions of dense subgroups of Lie groups on manifolds.
Actions of lattices on manifoldsread_more
HG G 43
30 September 2026
15:30-16:30 		Serge Cantat
Université de Rennes
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Geometry Seminar

Title On the product replacement algorithm in compact Lie groups
Speaker, Affiliation Serge Cantat, Université de Rennes
Date, Time 30 September 2026, 15:30-16:30
Location HG G 43
Abstract Let G be a compact Lie group. Let n be an integer. Given n elements g1, …, gn in G, one can choose one of the gi and replace it into its inverse, or into the product gigj for some j distinct from i; these basic operations do not change the subgroup of G generated by the gi. Doing so, one gets a group of transformations of Gn (generated by all these basic operations). The problem I will discuss is: what can be said on the dynamics of this group action on Gn? For instance, can we describe the closures of orbits, or the invariant probability measures? As we shall see, the answer is yes when n becomes large, in fact larger than an explicit constant that depends on G. This is based on a joint work with Christophe Dupont and Florestan Martin-Baillon, which complements previous works of Tsachik Gelander.
On the product replacement algorithm in compact Lie groupsread_more
HG G 43
7 October 2026
15:30-16:30
Details

Geometry Seminar

Title kein Seminar
Speaker, Affiliation
Date, Time 7 October 2026, 15:30-16:30
Location HG G 43
kein Seminar
HG G 43
14 October 2026
15:30-16:30 		Amina Abdurrahman
IHES
Details

Geometry Seminar

Title Hyperbolic homology 3-spheres, spectral gaps and torsion homology growth
Speaker, Affiliation Amina Abdurrahman, IHES
Date, Time 14 October 2026, 15:30-16:30
Location HG G 43
Abstract When does a sequence of hyperbolic 3-manifolds with volume going to infinity have exponentially growing torsion homology? For arithmetic towers, the work of Bergeron-Sengun-Venkatesh suggests a set of conditions that conjecturally imply exponential growth of torsion homology. Their work relies on Cheeger-Mueller's theorem, linking torsion homology and analytic torsion. For nice sequences of hyperbolic 3-manifolds we use a different approach to find a condition implying exponential torsion homology growth: we give a condition on the spectrum of the Laplacian. I will give several motivations for this condition and show how to construct concrete examples of sequences satisfying it. This is based on joint work with Anshul Adve, Vikram Giri, Ben Lowe and Jonathan Zung.
Hyperbolic homology 3-spheres, spectral gaps and torsion homology growthread_more
HG G 43
21 October 2026
15:30-16:30 		Dr. Camillo Brena
ETH Zurich, Switzerland
Details

Geometry Seminar

Title Cayley graphs and Ollivier-Ricci curvature
Speaker, Affiliation Dr. Camillo Brena, ETH Zurich, Switzerland
Date, Time 21 October 2026, 15:30-16:30
Location HG G 43
Abstract Riemannian manifolds with nonnegative Ricci curvature enjoy several interesting properties. For example, when complete, they have polynomial volume growth and, when compact, their universal covers split isometrically as products of compact manifolds and Euclidean spaces. In the discrete setting of graphs, several analogues of Ricci curvature have been proposed. This talk focuses on Ollivier's notion of Ricci curvature, introduced almost twenty years ago and based on optimal transport. The goal of this talk is to discuss the following rigidity result: if a finitely generated group has a Cayley graph with nonnegative Ollivier–Ricci curvature, then the group is virtually abelian and, in particular, has polynomial growth. This talk is based on joint works with Elia Bruè, Tom Hutchcroft, and Florentin Munch.
Cayley graphs and Ollivier-Ricci curvatureread_more
HG G 43
4 November 2026
15:30-16:30 		Max Riestenberg
MPI MiS Leipzig
Details

Geometry Seminar

Title Title T.B.A.
Speaker, Affiliation Max Riestenberg, MPI MiS Leipzig
Date, Time 4 November 2026, 15:30-16:30
Location HG G 43
Title T.B.A.
HG G 43
11 November 2026
15:30-16:30 		Claudius Zibrowius
Ruhr-Universität Bochum
Details

Geometry Seminar

Title Title T.B.A.
Speaker, Affiliation Claudius Zibrowius, Ruhr-Universität Bochum
Date, Time 11 November 2026, 15:30-16:30
Location HG G 43
Title T.B.A.
HG G 43
25 November 2026
15:30-16:30 		Susanna Zimmermann
Universität Basel
Details

Geometry Seminar

Title Title T.B.A.
Speaker, Affiliation Susanna Zimmermann, Universität Basel
Date, Time 25 November 2026, 15:30-16:30
Location HG G 43
Title T.B.A.
HG G 43
2 December 2026
15:30-16:30 		Renaud Detcherry
Institut de Mathématiques de Bourgogne
Details

Geometry Seminar

Title On Ivanov's finite-index Frattini conjecture and the AMU conjecture
Speaker, Affiliation Renaud Detcherry, Institut de Mathématiques de Bourgogne
Date, Time 2 December 2026, 15:30-16:30
Location HG G 43
Abstract The finite-index Frattini subgroup of a group G is the intersection of all its finite-index maximal subgroups. In 1966, Platonov proved that any finitely generated linear group has a nilpotent finite-index Frattini subgroup. In 1992, Ivanov conjectured that the same is true for a finitely generated subgroup of the mapping class group of a surface. We prove Ivanov's conjecture, based on our recent partial results on the Andersen–Masbaum–Ueno conjecture, that states that pseudo-Anosov elements have images of infinite order by SO(3)-WRT quantum representations at large enough levels. (joint work with Effie Kalfagianni)
On Ivanov's finite-index Frattini conjecture and the AMU conjectureread_more
HG G 43
9 December 2026
15:30-16:30 		Peter Huxford
Rice University
Details

Geometry Seminar

Title Title T.B.A.
Speaker, Affiliation Peter Huxford, Rice University
Date, Time 9 December 2026, 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: AS 26 SS 26 AS 25 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

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