Séminaire Géométrie et applications
organisé par l'équipe Géométrie
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Joé Brendel
Some constructions in almost toric geometry
16 novembre 2026 - 14:00Salle de séminaires IRMA
Almost toric geometry is a generalization of toric geometry, in which certain four-dimensional symplectic manifolds are encoded by two-dimensional base diagrams. The goal of this talk is to give an introduction to this topic, discuss many examples and then move to applications. If time permits we will discuss so-called Lagrangian needle's eyes. These are Lagrangian subspaces which exhibit intersection rigidity with the trace of certain Hamiltonian isotopies of Lagrangian tori. Almost toric fibrations are crucially used in their construction. -
Ibrahim Trifa
Rigidity and flexibility of exact Lagrangian submanifolds
16 novembre 2026 - 15:30Salle de séminaires IRMA
I will explain how to define a new class of "C^0 Lagrangians" in a cotangent bundle, that we call "bare Lagrangian branes", and that arise as Hausdorff limits of exact Lagrangian submanifolds with control on their Liouville primitives. I will address some rigidity and flexibility questions for such objects: if a bare Lagrangian brane is smooth, is it an exact Lagrangian brane? When does a bare Lagrangian brane admit a unique primitive (up to an additive constant)? The answer to this last question provides us with a lower regularity version of Arnaud's multidimensional Birkhoff theorem: if the support of a bare Lagrangian brane admitting a unique primitive is fixed by the time-1 flow of a Tonelli Hamiltonian, then it is a Lipschitz graph over the base. This is based on joint work with Skander Charfi. The talk is complementary to Charfi's talk on November 2, but no previous knowledge will be assumed. -
Yvon Fredrich
Lagrangian Intersections in Liouville Manifolds via Generating Functions
30 novembre 2026 - 14:00Salle de séminaires IRMA
Let (W, lambda) be a Liouville manifold and consider an exact Lagrangian isotopy (Lt) in W for t in [0,1]. We seek a lower bound for the intersection number of L0 and L1 when L0 and L1 intersect transversely. In the particular case where W is a cotangent bundle, analogous results are proved via the theory of generating families by Laudenbach and Sikorav in 1985 and by Chekanov in 1996. Laudenbach also proved such a result for a general Liouville manifold W in 1995, with the additional hypothesis pi1(W, L) = 0, pi2(W, L) = 0. -
Grazia Rago
TBA
7 décembre 2026 - 14:00Salle de séminaires IRMA
TBA -
Szabó Szilárd
TBA
14 décembre 2026 - 14:00Salle de séminaires IRMA
TBA -
Amandine Escalier
TBA
11 janvier 2027 - 14:00Salle de séminaires IRMA
TBA -
Michel Coornaert
Surjonctivité des sous-décalages de type fini
18 janvier 2027 - 14:00Salle de séminaires IRMA
On dit qu'un système dynamique est surjonctif si tout endomorphisme injectif du système est surjectif. Je présenterai une caractérisation géométrique de la surjonctivité pour les sous-décalages de type fini sur $\mathbb{Z}$. Cette caractérisation fait intervenir un ordre naturel sur l'ensemble des composantes irréductibles du sous-décalage. Il s'agit d'un travail en collaboration avec Tullio Ceccherini-Silberstein et Ville Salo. -
Corentin Fierobe
TBA
25 janvier 2027 - 14:00Salle de séminaires IRMA
TBA -
Yugang Zhang
TBA
1 février 2027 - 14:00Salle de séminaires IRMA
TBA -
Thomas Delzant
TBA
15 février 2027 - 14:00Salle de séminaires IRMA
TBA -
Antoine Ablondi
TBA
1 mars 2027 - 14:00Salle de séminaires IRMA
TBA -
Claire Schnoebelen
TBA
15 mars 2027 - 14:00Salle de séminaires IRMA
TBA -
Vladimir Chernov
Legendrian linking, Causality in classical and in Generalized spacetimes via Virtual Legendrian Linking.
19 avril 2027 - 14:00Salle de séminaires IRMA
Jointly with Stefan Nemrovski in our GAFA, GT and GP paper we showed Legendrian linking of the spheres of light rays through the two points does (nearly always) tell if the two event points in the universe are causally related, that is if they know of each other existence. We review these results and related Bott-Samelson type results of Nemirovski and myself and of Fraunenfelder-Labrousse-Shlenk. After that we introduce generalized spacetime that are singular Lorentz manifolds whose critical levels of a singular timelike Morse function cut them into globally hyperbolic pieces. Strong Cosmic censorship conjecture of Penrose suggests that if you delete black holes along horizons then what is left is globally hyperbolic. We introduce virtual Legendrian linking coming from the unit cotangent bundles of the spacetlike sections of such pieces and jointly with Sadykov we formulate the conjectures relating causality in generalized spacetimes to virtual Legendrian linking. In the remaining time we explore the theory results on virtual Legendrian links of Sadykov and myself.