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Autumn Semester 2026

Date / Time Speaker Title Location
21 September 2026
15:15-16:45 		Ibrahim Trifa
ETHZ
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Symplectic Geometry Seminar

Title A multidimensional Birkhoff Theorem for some $C^0$ Lagrangians
Speaker, Affiliation Ibrahim Trifa, ETHZ
Date, Time 21 September 2026, 15:15-16:45
Location HG G 43
Abstract In 1922, Birkhoff proved that an essential embedded closed curve that is invariant under a symplectic twist map of the cylinder is a Lipschitz graph over the zero section. There has been several works extending this theorem in higher dimension (Herman, Katznelson–Ornstein, Siburg, Bialy–Polterovich...). In 2010, Arnaud proved that a closed exact Lagrangian in the cotangent bundle of a closed manifold that is invariant under the flow of a Tonelli Hamiltonian is a graph over the base. Some improvements on this theorem have been made on one hand by Bernard-dos Santos and Amorim-Oh-dos Santos, who showed a version of this theorem for Lipschitz Lagrangian submanifolds, and on the other hand by Charfi who replaced the invariance assumption with a recurrence assumption (for a topology he defined and called "reduced complexity convergence"). In this talk, I will explain how to define a new class of "$C^0$ Lagrangians" for which the multidimensional Birkhoff theorem holds, using a new variant of the reduced complexity convergence topology. In particular, this class contains all images of continuous graphs by $C^1$ exact symplectomorphisms, which can be less regular than Lipschitz. This is based on a work in progress with Skander Charfi.
A multidimensional Birkhoff Theorem for some $C^0$ Lagrangiansread_more
HG G 43
5 October 2026
15:15-16:45 		Yael Karshon
Tel Aviv University
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Symplectic Geometry Seminar

Title Classification of complexity one Hamiltonian torus actions
Speaker, Affiliation Yael Karshon, Tel Aviv University
Date, Time 5 October 2026, 15:15-16:45
Location HG G 43
Abstract I will report on our (ongoing; partially completed) classification, joint with Sue Tolman, of Hamiltonian torus actions of complexity one.
Classification of complexity one Hamiltonian torus actionsread_more
HG G 43
12 October 2026
15:15-16:45 		Misha Temkin
University of Freiburg
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Symplectic Geometry Seminar

Title Interlevel persistence from a manifold standpoint
Speaker, Affiliation Misha Temkin, University of Freiburg
Date, Time 12 October 2026, 15:15-16:45
Location HG G 43
Abstract For a function f on a topological space X, Cohen-Steiner--Edelsbrunner--Harer defined an extended barcode of f. It is a combinatorial gadget that compactly stores information about, in particular, homology of any interlevel set f^{-1}([a,b]) (over a field F). When X is a closed manifold and f is Morse without multiple critical values, we propose an equivalent, geometrical definition of extended barcode. It relies on a description of relative position of two flags in a vector space (known as Bruhat decomposition). We then use this framework to address the following question: given two cobordisms equipped with Morse functions and the glueing diffeomorphism, how to express the barcode of the resulting function on a glued manifold in terms of the given data? Time permitting, we will also speculate about the relation of our constructions to the theory of Legendrian links.
Interlevel persistence from a manifold standpointread_more
HG G 43
19 October 2026
15:15-16:45 		Reto Kaufmann
ETHZ
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Symplectic Geometry Seminar

Title Visible Lagrangians in Toric Symplectic Manifolds
Speaker, Affiliation Reto Kaufmann, ETHZ
Date, Time 19 October 2026, 15:15-16:45
Location HG G 43
Abstract Following ideas of Symington, Evans calls a Lagrangian in the cotangent bundle of a torus visible if the moment map restricts to a surjective submersion onto a submanifold of the moment space. It follows from the Lagrangian condition that the only possible images are rational affine subspaces (Evans ’23). In this talk, we extend the notion of visibility to smooth Lagrangians in toric symplectic manifolds and ask: given an affine slice of the moment polyhedron, can we find visible Lagrangian(s) whose moment image is the prescribed slice? This is partly based on joint work with Joé Brendel and partly on work in progress.
Visible Lagrangians in Toric Symplectic Manifoldsread_more
HG G 43
26 October 2026
15:15-16:30 		John Miller
ETHZ
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Symplectic Geometry Seminar

Title TPCs and Filtered Topology
Speaker, Affiliation John Miller, ETHZ
Date, Time 26 October 2026, 15:15-16:30
Location HG G 43
Abstract I will review some classical notions of complexity as well as the more recent theory of persistence and triangulated persistence categories (TPCs) as defined by Biran, Cornea, and Zhang. Following this, I will discuss applications of these to the study of filtered topology. In particular, I will present a suitable category of filtered topological spaces detailing a few key constructions and properties, before going on to show how one can use this to build an associated TPC by passing to stable homotopy and conclude with a couple of interesting results.
TPCs and Filtered Topologyread_more
HG G 43
* 26 October 2026
16:30-17:45 		Baptiste Serraille
ETHZ
Details

Symplectic Geometry Seminar

Title A counterexample to the Viterbo conjecture
Speaker, Affiliation Baptiste Serraille, ETHZ
Date, Time 26 October 2026, 16:30-17:45
Location HG G 43
Abstract In this talk, I will present a counterexample to the Viterbo conjecture. The conjecture predicts that Viterbo's spectral metric is bounded on the space of Lagrangians Hamiltonian isotopic to the zero section in the disk cotangent bundle $D^*Q$ for all manifold $Q$. I will first go through the definition of Viterbo's spectral metric and then explain how a magnetic Hamiltonian can, under some topological assumption on $Q$, yield a counterexample to the conjecture. I will also sketch the proof of the complete classifications of the surfaces for which the Viterbo conjecture holds. This is joint work with Filip Broćić and Ibrahim Trifa.
A counterexample to the Viterbo conjectureread_more
HG G 43
2 November 2026
15:15-16:45 		Marc Kegel
Sevilla University
Details

Symplectic Geometry Seminar

Title Title T.B.A.
Speaker, Affiliation Marc Kegel, Sevilla University
Date, Time 2 November 2026, 15:15-16:45
Location HG G 43
Abstract TBA
Title T.B.A.read_more
HG G 43
9 November 2026
15:15-16:45 		Alexia Corradini
Cambridge University
Details

Symplectic Geometry Seminar

Title Title T.B.A.
Speaker, Affiliation Alexia Corradini, Cambridge University
Date, Time 9 November 2026, 15:15-16:45
Location HG G 43
Abstract TBA
Title T.B.A.read_more
HG G 43
16 November 2026
15:15-16:45 		Asaf Kapota
Hebrew University Jerusalem
Details

Symplectic Geometry Seminar

Title Title T.B.A.
Speaker, Affiliation Asaf Kapota, Hebrew University Jerusalem
Date, Time 16 November 2026, 15:15-16:45
Location HG G 43
Abstract TBA
Title T.B.A.read_more
HG G 43
23 November 2026
15:15-16:45 		Jean Gutt
Université libre de Bruxelles
Details

Symplectic Geometry Seminar

Title Title T.B.A.
Speaker, Affiliation Jean Gutt, Université libre de Bruxelles
Date, Time 23 November 2026, 15:15-16:45
Location HG G 43
Abstract TBA
Title T.B.A.read_more
HG G 43
30 November 2026
15:15-16:45 		Maarten Mol
Toronto University
Details

Symplectic Geometry Seminar

Title Title T.B.A.
Speaker, Affiliation Maarten Mol, Toronto University
Date, Time 30 November 2026, 15:15-16:45
Location HG G 43
Abstract TBA
Title T.B.A.read_more
HG G 43
7 December 2026
15:15-16:45 		Grigory Mikhalkin
Université de Genève
Details

Symplectic Geometry Seminar

Title Title T.B.A.
Speaker, Affiliation Grigory Mikhalkin, Université de Genève
Date, Time 7 December 2026, 15:15-16:45
Location HG G 43
Abstract TBA
Title T.B.A.read_more
HG G 43
14 December 2026
15:15-16:45 		Alexandru Oancea
Université de Strasbourg
Details

Symplectic Geometry Seminar

Title Title T.B.A.
Speaker, Affiliation Alexandru Oancea, Université de Strasbourg
Date, Time 14 December 2026, 15:15-16:45
Location HG G 43
Abstract TBA
Title T.B.A.read_more
HG G 43

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