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Autumn Semester 2026

Date / Time Speaker Title Location
* 18 September 2026
16:15-17:15 		Natasha Diederen
UCL
Details

Geometry Graduate Colloquium

Title Oriented integral varifolds with curvature and boundary
Speaker, Affiliation Natasha Diederen, UCL
Date, Time 18 September 2026, 16:15-17:15
Location HG G 19.2
Abstract A varifold is a generalisation of a surface well-suited to addressing geometric variational problems. After reviewing some preliminary results and examples, we will introduce a class of varifolds that have a weak notion of orientation and second fundamental form. We will then demonstrate the utility of this class in proving the existence of minimisers to the Canham-Helfrich energy, a curvature-dependent energy that models the shape of cell membranes. Time permitting, we will discuss the development of a boundary operator for oriented varifolds as a way to address the multi-phase Canham-Helfrich problem. This is joint work in progress with C. Bellettini.
Oriented integral varifolds with curvature and boundaryread_more
HG G 19.2
24 September 2026
16:15-17:15 		Jonah Mendel
Rice University
Details

Geometry Graduate Colloquium

Title Constructions of arithmetic groups acting on products of trees
Speaker, Affiliation Jonah Mendel, Rice University
Date, Time 24 September 2026, 16:15-17:15
Location HG E 41
Abstract Stix and Vdovina used quaternion algebras over function fields to construct explicit families of torsion-free arithmetic lattices acting simply transitively on products of Bruhat-Tits trees of equal regularity. In particular, they obtained a lattice of Euler characteristic one over 𝔽3(t) acting on a product of two trees. In this talk, I will discuss analogous constructions over number fields. I will describe classification results for lattices of small Euler characteristic and present new infinite families of torsion-free lattices acting simply transitively on products of trees of equal regularity. This talk contains joint work with Jakob Stix, Alina Vdovina, and Jiahui Yu.
Constructions of arithmetic groups acting on products of treesread_more
HG E 41
* 8 October 2026
16:00-17:00
Details

Geometry Graduate Colloquium

Title Paul Bernays lecture - Akshay Venkatesh
Speaker, Affiliation
Date, Time 8 October 2026, 16:00-17:00
Location
More information https://math.ethz.ch/news-and-events/events/lecture-series/paul-bernays-lectures.html
Paul Bernays lecture - Akshay Venkateshread_more
15 October 2026
16:15-17:15 		Ilayda Demir
Paris Cité and Sorbonne
Details

Geometry Graduate Colloquium

Title Khovanov homology and the Rasmussen invariant
Speaker, Affiliation Ilayda Demir, Paris Cité and Sorbonne
Date, Time 15 October 2026, 16:15-17:15
Location HG E 41
Abstract Short after the definition of the Khovanov homology at the very end of the 20th century by Mikhail Khovanov, Jacob Rasmussen defined a knot invariant using a deformation of Khovanov homology, namely Lee-Khovanov homology. The Milnor conjecture concerning the slice genus of torus knots, namely g4(T(p,q)) = ½(p-1)(q-1), which was originally proved using gauge theory by Kronheimer and Mrowka was reproved using the Rasmussen invariant. This first purely combinatorial proof is considered to be the first application of Khovanov homology.
Khovanov homology and the Rasmussen invariantread_more
HG E 41
22 October 2026
16:15-17:15 		Ibrahim Trifa
ETH Zurich, Switzerland
Details

Geometry Graduate Colloquium

Title Some topics in C^0 symplectic topology
Speaker, Affiliation Ibrahim Trifa, ETH Zurich, Switzerland
Date, Time 22 October 2026, 16:15-17:15
Location HG E 41
Abstract $C^0$ symplectic topology investigates the behaviour of symplectic objects under $C^0$ limits. In this talk, I will give a brief introduction to symplectic topology, and then present some ideas of a proof of the Eliashberg-Gromov rigidity theorem, which states that the set of symplectic diffeomorphisms is closed within the space of diffeomorphisms for the $C^0$ topology. This result led to a natural definition of symplectic homeomorphisms, and opened the way towards the study of $C^0$ symplectic topology. If time permits, I will talk about some other topics in $C^0$ symplectic topology, such as $C^0$ Lagrangian rigidity and/or the structure of the group of Hamiltonian homeomorphisms.
Some topics in C^0 symplectic topologyread_more
HG E 41
29 October 2026
16:15-17:15 		Lily Natasha Wartman
Rice University
Details

Geometry Graduate Colloquium

Title Hyperbolic structure on the figure 8 knot complement
Speaker, Affiliation Lily Natasha Wartman, Rice University
Date, Time 29 October 2026, 16:15-17:15
Location HG E 41
Abstract In this talk I’ll prove that the figure 8 knot complement has hyperbolic structure. We will first decompose the figure eight knot into two polyhedra, and then put a hyperbolic structure on the tetrahedra. I will introduce edge invariants and edge gluing equations that allow us to explicitly construct a hyperbolic structure on the figure 8 knot complement.
Hyperbolic structure on the figure 8 knot complementread_more
HG E 41
5 November 2026
16:15-17:15 		David Lenze
Karlsruhe Institute of Technology
Details

Geometry Graduate Colloquium

Title Wasserstein spaces through the lens of metric geometry
Speaker, Affiliation David Lenze, Karlsruhe Institute of Technology
Date, Time 5 November 2026, 16:15-17:15
Location HG E 41
Abstract I will discuss Wasserstein spaces over Riemannian manifolds and explain how studying their infinitesimal geometry allows one to derive global rigidity results. As a consequence, I will show that the metric geometry of the Wasserstein space remembers the underlying manifold up to isometry. I will also describe its full isometry group, highlighting the role of Euclidean factors and the exceptional behaviour of the real line.
Wasserstein spaces through the lens of metric geometryread_more
HG E 41
12 November 2026
16:15-17:15 		Beatrice Bernasconi
ETH Zurich, Switzerland
Details

Geometry Graduate Colloquium

Title Length Functions and Dynamical Invariants in the Cremona Group.
Speaker, Affiliation Beatrice Bernasconi, ETH Zurich, Switzerland
Date, Time 12 November 2026, 16:15-17:15
Location HG E 41
Abstract The plane Cremona group Bir(P^2) is an interesting object that has been studied for over 150 years, and offers a rich structure that can be studied from different perspectives and point of views. We focus on a dynamical perspective: this point of view allows to study and classify elements in Bir(P^2) up to birational conjugacy. In this talk, we give an overview of the construction of the group, then we define and study various length functions and dynamical invariants that allow us to give a classification of the Cremona maps.
Length Functions and Dynamical Invariants in the Cremona Group.read_more
HG E 41
19 November 2026
16:15-17:15 		Ekaterina Kuritsina
Université Paris-Est Créteil
Details

Geometry Graduate Colloquium

Title The Closure of Finitely Supported Mapping Classes on Infinite-Type Surfaces
Speaker, Affiliation Ekaterina Kuritsina, Université Paris-Est Créteil
Date, Time 19 November 2026, 16:15-17:15
Location HG E 41
The Closure of Finitely Supported Mapping Classes on Infinite-Type Surfaces
HG E 41
26 November 2026
16:15-17:15 		Aviv Taller
EPFL
Details

Geometry Graduate Colloquium

Title Towards superrigidity for actions on CAT(0) cube complexes without a rank assumption
Speaker, Affiliation Aviv Taller, EPFL
Date, Time 26 November 2026, 16:15-17:15
Location HG E 41
Towards superrigidity for actions on CAT(0) cube complexes without a rank assumption
HG E 41
3 December 2026
16:15-17:15 		Jessica Anzanello
University of Milan
Details

Geometry Graduate Colloquium

Title Fixed-point-free elements in intransitive permutation groups
Speaker, Affiliation Jessica Anzanello, University of Milan
Date, Time 3 December 2026, 16:15-17:15
Location
Fixed-point-free elements in intransitive permutation groups
10 December 2026
16:15-17:15 		Dr. Viola Giovannini
ETH Zurich, Switzerland
Details

Geometry Graduate Colloquium

Title Title T.B.A.
Speaker, Affiliation Dr. Viola Giovannini, ETH Zurich, Switzerland
Date, Time 10 December 2026, 16:15-17:15
Location HG E 41
Title T.B.A.
HG E 41

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