Séminaire des doctorants du LAGA

Programme et résumés des exposés

Date	Orateur (institution)	Titre	Résumé
26/09/2025	Nicolas Guès (LAGA, Université Sorbonne Paris-Nord)	Une introduction aux groupes modulaires de surfaces English version: An introduction to mapping class groups	Les groupes modulaires de surfaces sont des objets mystérieux situés à l’intersection de la topologie, de la géométrie, de la théorie des groupes et de la dynamique. Malgré la simplicité de leur définition, de nombreuses questions fondamentales à leur sujet restent ouvertes à ce jour. J’expliquerai ce que sont ces groupes et à quel point ils sont omniprésents en géométrie. English version: The mapping class groups of surfaces are mysterious objects which stand at the crossroad of topology, geometry, group theory, and dynamics. Despite the simplicity of their definition, a lot of basic questions about them remain open to this day. I will explain what they are and how ubiquitous they are in modern geometry.
09/10/2025	Dominik Schrimpel (LAGA, Université Sorbonne Paris-Nord)	An introduction to algebraic K-theory	As an excuse to learn the basics of algebraic K-theory myself, I will introduce this magical invariant that has become so central in modern mathematics. Don’t worry though, I will focus mostly on its classical algebraic side, including the delight of encountering up to seven seemingly different but secretly equivalent definitions. If time permits, I will venture into some modern perspectives and applications in “brave new algebra.”
16/10/2025	David Nahmani (LAGA, Université Sorbonne Paris-Nord)	Equations différentielles et contrôle optimal pour lutter contre les virus transmis par les moustiques English version: Differential equations and optimal control to struggle against mosquito-borne viruses	Les moustiques transmettent certains virus à l’être humain, tels que la dengue, le chikungunya, le virus Zika et la fièvre jaune. Cependant, lorsqu’ils sont infectés par la bactérie Wolbachia, leur capacité à transmettre ces virus est considérablement réduite. Ainsi, remplacer une population de moustiques sauvages par une population de moustiques infectés par Wolbachia constitue une option prometteuse pour éradiquer ces virus. Cette stratégie est appelée remplacement de population. Les mathématiques peuvent aider les biologistes à optimiser cette stratégie. Dans cette présentation, j’exposerai le modèle mathématique de la dynamique de population : une équation différentielle non linéaire bistable. J’en présenterai ensuite quelques propriétés simples mais intéressantes de ses solutions. Enfin, je passerai rapidement en revue certains résultats de contrôle optimal qui offrent des pistes concrètes pour la stratégie écologique. English version: Mosquitoes transmit some viruses to the human being, such as dengue fever, chikungunya, Zika fever and yellow fever, but when they are infected with the bacterium Wolbachia, their ability to transmit them is significantly reduced. Therefore, replacing a wild mosquito population by a population of Wolbachia-infected mosquitoes is a valuable option to eradicate those viruses. This strategy is called population replacement. Mathematics can help biologists to optimize this strategy. In this presentation, I will expose the mathematical model of the population dynamics: a bistable nonlinear differential equation. Then, I will give some basic but interesting properties on its solutions. I will finally go quickly over some optimal control results that give a practical hint on the ecological strategy.
06/11/2025	Nicolas Conanec (LAGA, Université Sorbonne Paris-Nord)	Introduction to Nonparametric Statistics	When we talk about inferential statistics they are two types of problems. The ones where the thing we want to estimate lives in a space of finite dimension and the ones in non finite dimension. The former is usually called parametric statistics and the latter non-parametric statistics. In this talk we will first make a introduction on the basic notions about statistics. And then we will talk about the classical techniques used to solve nonparametric estimation problems such as kernel estimators or projection estimators.
20/11/2025	Hari Sudarsan (LMO, Université Paris-Saclay)	How lower K-groups detect geometric properties of rings	Algebraic K-theory is a cohomology theory that relates to any ring A, a family of groups known as the K-groups of A. Studying these K-groups has been shown to provide information of an arithmetic, topological or geometric nature about the ring in question. In this talk I will discuss how some of the lower K-groups of rings are defined explicitly and how studying them provides us with geometric information about the ring, and can even help us detect regularity or smoothness.
04/12/2025	Valentin Kraemer (LAGA, Université Sorbonne Paris-Nord)	Introduction of Domain decomposition in an industrial code	For industrial codes, solving PDEs requires efficient parallelization strate- gies due to the very large number of unknowns involved. Computer scientists have drawn inspiration from many domains, from video games to mathemat- ics. Unfortunately, I’m not particularly good at video games... That’s why I propose instead to explore how mathematics—and especially domain decompo- sition—can help us improve the numerical simulations of nuclear power plants.
18/12/2025	Régis Aolo (LAMA, Université Paris-Est-Créteil-Val-de-Marne)	TBA	TBA
08/01/2026	TBA	TBA	TBA
22/01/2026	Thomas De Myttenaere (LAGA, Université Sorbonne Paris-Nord)	TBA	TBA
05/02/2026	TBA	TBA	TBA
19/02/2026	TBA	TBA	TBA
05/03/2026	TBA	TBA	TBA
02/04/2026	TBA	TBA	TBA
16/04/2026	TBA	TBA	TBA