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Spring Semester 2026

Date / Time Speaker Title Location
* 26 January 2026
16:00-17:00 		Stefan Haller
Universität Wien
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Symplectic Geometry Seminar

Title Spectral invariants of the Rumin complex on contact manifolds and beyond
Speaker, Affiliation Stefan Haller, Universität Wien
Date, Time 26 January 2026, 16:00-17:00
Location HG G 19.1
Abstract On a contact manifold, Rumin's complex provides a sequence of differential operators that is intrinsic to the contact structure and computes de~Rham cohomology. This is a Rockland complex, the analogue of an elliptic complex in the Heisenberg calculus. Subelliptic analysis permits to define and study associated spectral invariants. In particular, the analytic torsion and the eta invariant of Rumin's contact complex have been compared to Riemannian an CR-invariants by Biquard-Herzlich-Rumin, Rumin-Seshadri, and Albin-Quan. While Rumin's complex can be defined for a broad class of filtered (Carnot) manifolds, one 5-dimensional geometry stands out because its Rumin complex is as well behaved as the contact analogue. This geometry is determined by a generic rank two distribution (i.e. 2-plane field) in dimension five, a.k.a. (2,3,5) distribution. Equivalently, it can be characterized as a particular Cartan geometry associated with the exceptional Lie group G2. In this talk we will recall the contact case and discuss recent results on the analytic torsion and the eta invariant of (2,3,5) distributions.
Spectral invariants of the Rumin complex on contact manifolds and beyondread_more
HG G 19.1
23 February 2026
15:15-16:30 		Christian Urech
ETHZ
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Symplectic Geometry Seminar

Title Characterizing varieties by their groups of birational transformations
Speaker, Affiliation Christian Urech, ETHZ
Date, Time 23 February 2026, 15:15-16:30
Location HG G 43
Abstract To an algebraic variety X one associates its group of birational transformations Bir(X). In the last decades, these groups and their rich algebraic, geometric, and dynamic structures have attracted a great deal of interest. In this talk, I will explain how the group structure of Bir(X) characterizes in many important cases the variety X. In particular, we will obtain new rationality criteria.
Characterizing varieties by their groups of birational transformationsread_more
HG G 43
2 March 2026
15:15-16:30 		Elliot Gathercole
Lancaster University
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Symplectic Geometry Seminar

Title Widths of Complements of Skeleta in Projective Space
Speaker, Affiliation Elliot Gathercole, Lancaster University
Date, Time 2 March 2026, 15:15-16:30
Location HG G 43
Abstract Given an effective divisor D in projective space P^n (equipped with its usual symplectic form), we obtain a distinguished subset, the skeleton, L, which has many interesting symplectic properties. When D is smooth and of degree >1, L is known to be a barrier, meaning that the Gromov width of P^n-L is strictly smaller than that of P^n. We can ask if a similar result holds if D is not smooth. This talk will give a partial answer to this question. We will see how to obtain an upper bound for the Gromov width of P^n-L for a certain class of non-smooth divisors D using neck-stretching, which is tight in the case of a generic arrangement of at least n+1 hyperplanes.
Widths of Complements of Skeleta in Projective Spaceread_more
HG G 43
9 March 2026
15:15-16:30 		Joshua Sabloff
Haverford College
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Symplectic Geometry Seminar

Title Weak Relative Calabi-Yau Structures for Legendrian Contact Homology
Speaker, Affiliation Joshua Sabloff, Haverford College
Date, Time 9 March 2026, 15:15-16:30
Location HG G 43
Abstract The Legendrian Contact Homology (LCH) differential graded algebra (DGA) was among the first, and is still among the most important, non-classical invariants of Legendrian knots. In this talk, I will tell a story that builds up ever more sophisticated analogues of Poincare Duality as we delve more deeply into the structure of the DGA. Despite the algebraic nature of the results, I promise pictures, examples, and analogies with Morse Theory. This is joint work with Jason Ma (Duke).
Weak Relative Calabi-Yau Structures for Legendrian Contact Homologyread_more
HG G 43
16 March 2026
15:15-16:30 		Alberto Enciso
ICMAT
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Symplectic Geometry Seminar

Title Diffeomorphism-based convex integration schemes for incompressible fluid flows
Speaker, Affiliation Alberto Enciso, ICMAT
Date, Time 16 March 2026, 15:15-16:30
Location HG G 43
Abstract We will review how one can design convex integration schemes using volume-preserving diffeomorphisms to address problems that are typically not amenable to more traditional schemes. To illustrate this philosophy, we will consider the construction of rough steady Euler flows with certain prescribed topological properties and of Hölder continuous dissipative solutions to ideal MHD. The talk is based on joint work with Daniel Peralta-Salas and Javier Peñafiel-Tomás.
Diffeomorphism-based convex integration schemes for incompressible fluid flowsread_more
HG G 43
* 16 March 2026
16:30-17:45 		Octav Cornea
Montreal University
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Symplectic Geometry Seminar

Title Non precompactness of some spaces of Lagrangian submanifolds
Speaker, Affiliation Octav Cornea, Montreal University
Date, Time 16 March 2026, 16:30-17:45
Location HG G 43
Abstract This talk, based on joint work with Ambrosioni and Biran, will discuss some metric properties of some spaces of Lagrangian submanifolds endowed with the spectral metric. In particular, I will show how some natural notions of complexity in triangulated categories can be applied to some triangulated persistence refinements of Fukaya categories to identify examples of such metric spaces that are not precompact.
Non precompactness of some spaces of Lagrangian submanifoldsread_more
HG G 43
23 March 2026
15:15-16:30 		Johanna Bimmermann
Oxford
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Symplectic Geometry Seminar

Title Systoles, diastoles and the Hofer–Zehnder capacity
Speaker, Affiliation Johanna Bimmermann, Oxford
Date, Time 23 March 2026, 15:15-16:30
Location HG G 43
Abstract The Hofer–Zehnder capacity is a numerical symplectic invariant defined via Hamiltonian dynamics and closely related to the existence of periodic orbits. In this talk, I survey known and still missing results on the Hofer–Zehnder capacity of subsets of (co-)tangent bundles, with an emphasis on explicit computations for disk bundles. Lower bounds are typically obtained via Riemannian billiards, while upper bounds rely on Floer theoretic methods. So far, all explicit computations are restricted to highly degenerate settings, such as constant curvature metrics or more generally symmetric spaces. I will report on work in progress aimed at extending these techniques to less degenerate Riemannian metrics and relates its value to certain diastolic quantities.
Systoles, diastoles and the Hofer–Zehnder capacity read_more
HG G 43
30 March 2026
15:15-16:30 		Marco Mazzucchelli
Sorbonne Université (IMJ-PRG)
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Symplectic Geometry Seminar

Title Closed geodesics and the first Betti numbers
Speaker, Affiliation Marco Mazzucchelli, Sorbonne Université (IMJ-PRG)
Date, Time 30 March 2026, 15:15-16:30
Location HG G 43
Abstract In this talk, based on joint work with Gonzalo Contreras, I will sketch a proof of the following theorem: on any closed manifold of dimension at least two with non-zero first Betti number, a C∞ generic Riemannian metric has infinitely many closed geodesics, and indeed closed geodesics of arbitrarily large length. I will derive this result as a consequence of the following new theorem of independent interest: the existence of minimal closed geodesics, in the sense of Aubry-Mather theory, implies the existence of a transverse homoclinic, and thus of a horseshoe, for the geodesic flow of a suitable C∞-close Riemannian metric.
Closed geodesics and the first Betti numbersread_more
HG G 43
13 April 2026
15:15-16:30 		Jean-Philippe Chassé
Université de Montréal
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Symplectic Geometry Seminar

Title On Lagrangian flux and monodromy
Speaker, Affiliation Jean-Philippe Chassé, Université de Montréal
Date, Time 13 April 2026, 15:15-16:30
Location HG G 43
Abstract Associated to any loop of Lagrangian submanifolds is a cohomology class of the basepoint: its flux. However, contrary to the symplectic setting, this does not define a morphism on the fundamental group of the space of Lagrangian submanifolds. I will explain how this can be rectified by considering the monodromy of the loop and how the algebraic properties of the ensuing flux-monodromy morphism are related to topological properties of the Hamiltonian orbit of the basepoint. Finally, I will provide explicit computations for certain Lagrangian tori, revealing novel structure in the associated fundamental groups. This is joint work with Joé Brendel and Rémi Leclercq.
On Lagrangian flux and monodromyread_more
HG G 43
27 April 2026
15:15-16:30 		Kai Cieliebak
Details

Symplectic Geometry Seminar

Title Title T.B.A.
Speaker, Affiliation Kai Cieliebak,
Date, Time 27 April 2026, 15:15-16:30
Location HG G 43
Title T.B.A.
HG G 43
4 May 2026
15:15-16:30 		Yasha Eliashberg
Stanford
Details

Symplectic Geometry Seminar

Title Title T.B.A.
Speaker, Affiliation Yasha Eliashberg, Stanford
Date, Time 4 May 2026, 15:15-16:30
Location HG G 43
Title T.B.A.
HG G 43
11 May 2026
15:15-16:30 		Beomjun Sohn
RWTH Aachen
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Symplectic Geometry Seminar

Title Topological entropy under small area perturbation
Speaker, Affiliation Beomjun Sohn, RWTH Aachen
Date, Time 11 May 2026, 15:15-16:30
Location HG G 43
Abstract In this talk, we present a new robustness result for the topological entropy of Hamiltonian diffeomorphisms on closed surfaces. Topological entropy is a fundamental measure of orbital complexity in dynamical systems, capturing chaotic behavior through a single non-negative value. We prove that if a Hamiltonian diffeomorphism has positive entropy, then any perturbation supported in a topological disk of sufficiently small area still has positive entropy. The proof relies on a new braid stability result derived from Floer-theoretic braids of fixed points, which can be related to the area of the support. This talk is based on ongiong joint work with Marcelo Alves and Matthias Meiwes.
Topological entropy under small area perturbationread_more
HG G 43
18 May 2026
15:15-16:30 		Bernhard Albach
RWTH Aachen
Details

Symplectic Geometry Seminar

Title Title T.B.A.
Speaker, Affiliation Bernhard Albach, RWTH Aachen
Date, Time 18 May 2026, 15:15-16:30
Location HG G 43
Title T.B.A.
HG G 43

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