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Yenni Cherik

08/12/2022 à 17:00:00 - 08/12/2022 à 18:00:00

Titre du séminaire

Inner geometry of the Milnor fibers

Résumé

Let (X,0) be a complex surface germ with an isolated singularity at the origin of C^n and f:(X,0)->(C,0) be a non constant holomorphic function. We will study the inner metric of the Milnor fibers f^(-1)(t) by defining a family of metric invariants called inner-rates. After  that i will state and prove the inner-rates formula which provide us a concrete way of computing the inner rates and, on the other hand, relate them with the polar curves of f. We will end the talk with an application of the inner rates to compute the integral of the gaussian curvature on the Milnor fibers.

Institution de l'oratrice/orateur

Institut mathématique de Marseille

Thème de recherche

Compréhensible

Salle

4

Philippe Castillon

08/12/2022 à 14:00:00 - 08/12/2022 à 15:00:00

Titre du séminaire

Prescription de la courbure de Gauss des convexes de l’espace hyperbolique

Résumé

La mesure de courbure d’un convexe est une mesure sur la sphère unité qui étend la notion de courbure de Gauss aux convexes non lisses. Le problème d’Alexandrov consiste à déterminer les convexes dont la mesure de courbure est donnée à priori. Dans l’espace euclidien, A.D. Alexandrov a donné une condition nécessaire et suffisante sur la mesure donnée pour que ce problème ait une solution. Dans cet exposé je traiterai le cas des convexes de l’espace hyperbolique pour lesquels on a un résultat analogue. La preuve repose sur des outils de géométrie intégrale pour montrer que la condition est nécessaire, et sur une forme faible d’une équation de Monge-Ampère pour montrer qu’elle est suffisante. Travail en collaboration avec Jérôme Bertrand.

Institution de l'oratrice/orateur

Montpellier

Thème de recherche

Théorie spectrale et géométrie

Salle

4

Marco Marengon

02/12/2022 à 10:30:00 - 02/12/2022 à 11:30:00

Titre du séminaire

Some results and conjectures on the rank of some knot homologies

Résumé

Given a knot in the 3-sphere, one can associate some knot homologies with it, among which knot Floer homology and (reduced) Khovanov homology. Motivated by Fox-Milnor's obstruction for slice knots, we prove that all knots in a certain family have these homologies with total rank being a square integer. Moreover, we conjecture that the rank of knot Floer homology is congruent to 1 modulo 8 for all slice knots, and we prove this fact for a subfamily of slice knots, namely fusion number 1 ribbon knots. This is a joint work with Hockenhull and Willis, and partially also with Dunfield and Gong.

Thème de recherche

Topologie

Salle

4

Roman Prosanov

01/12/2022 à 14:00:00 - 01/12/2022 à 15:00:00

Titre du séminaire

On hyperbolic 3-manifolds with polyhedral boundary

Résumé

It is known that convex bodies in the model 3-spaces of constant curvature are rigid with respect to the induced intrinsic metric on the boundary. This story has two classical chapters: the rigidity of convex polyhedra and the rigidity of smooth convex bodies, though there is also a common generalization obtained by Pogorelov.
Similarly to this, Jean-Marc Schlenker proved that hyperbolic metrics with smooth strictly convex boundary on a compact hyperbolizable 3-manifold M are rigid with respect to the induced metric on the boundary (and also with respect to the dual metric). It is reasonable to expect that similar results should hold also for polyhedral boundaries, and eventually for general convex boundaries. Curiously enough, no polyhedral counterparts were proven up to now, though some partial progress was made by François Fillastre. One of the main difficulties is that convex hyperbolic cone-metrics on the boundary of M (which is a standard intrinsic description of what we expect to be the induced metric on a polyhedral boundary) might admit not so polyhedral realizations, which are hard to handle or to exclude. A prototypical example is the boundary of a convex core bent along an irrational lamination.
I will present a recent work proving the rigidity (and the dual rigidity) of hyperbolic metrics on M with convex polyhedral boundary under mild additional assumptions. As another outcome, it follows that convex cocompact hyperbolic metrics on the interior on M with the convex cores that are "almost polyhedral" are globally rigid with respect to the induced metric on the boundary of the convex core, and are infinitesimally rigid with respect to the bending lamination. This is a step towards conjectures of William Thurston.

Institution de l'oratrice/orateur

Vienne

Thème de recherche

Théorie spectrale et géométrie

Salle

4

Alice Contat

29/11/2022 à 14:00:00 - 29/11/2022 à 15:00:00

Titre du séminaire

Parking sur des arbres de Cayley & Frozen Erdös--Rényi

Résumé

Consider a uniform rooted Cayley tree Tn with n vertices and let m cars arrive sequentially, independently, and uniformly on its vertices. Each car tries to park on its arrival node, and if the spot is already occupied, it drives towards the root of the tree and parks as soon as possible. Using combinatorial enumeration, Lackner & Panholzer established a phase transition for this process when m is approximately n/2. We couple this model with a variation of the classical Erdös--Rényi random graph process. This enables us to describe completely the phase transition for the size of the components of parked cars using a modification of the standard multiplicative coalescent which we named the frozen multiplicative coalescent. The talk is based on joint work with Nicolas Curien.

Institution de l'oratrice/orateur

Orsay

Thème de recherche

Probabilités

Salle

4

Clotilde Fermanian Kammerer

28/11/2022 à 13:30:00 - 28/11/2022 à 14:30:00

Titre du séminaire

Semi-classical analysis of sub-Laplacians on step 2 Nilmanifods

Résumé

In this talk, we will present a semi-classical approach of quantum limits for a sub-Laplacian on a step 2 nilmanifold. These manifolds are obtained by (left)-quotienting a nilpotent Lie group by one of its co-compact sub-groups. They present a rich geometry ; for example, they can enjoy a contact or a quasi-contact structure. We will consider sequences of eigenfunctions of a sub-Laplacian defined on this manifold and we will describe some results about the structure of the weak limits of densities associated with these sequences. These results have been obtained in collaboration with Véronique Fischer and Steven Flynn (University of Bath).

Thème de recherche

Physique mathématique

Salle

1, Tour Irma
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