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X-ORIGINAL-URL:https://www.math.ens.psl.eu
X-WR-CALDESC:évènements pour Département de mathématiques et applications
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TZID:Europe/Paris
BEGIN:DAYLIGHT
TZOFFSETFROM:+0100
TZOFFSETTO:+0200
TZNAME:CEST
DTSTART:20260329T010000
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DTSTART:20261025T010000
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BEGIN:VEVENT
DTSTART;TZID=Europe/Paris:20260407T093000
DTEND;TZID=Europe/Paris:20260407T123000
DTSTAMP:20260403T233438
CREATED:20251018T115430Z
LAST-MODIFIED:20260326T185638Z
UID:20142-1775554200-1775565000@www.math.ens.psl.eu
SUMMARY:Computer-Assisted Proofs of 3D Euler Singularity and Nonuniqueness of Leray–Hopf Solutions for the Unforced 3D Navier–Stokes Equations
DESCRIPTION:Speaker: Thomas Hou (Caltech) \n\n\n\nThe talk will take place in « Amphithéâtre Galois »\, underground near the math library\, 45 rue d’Ulm\, Paris \n\n\n\nWhether the 3D incompressible Euler equations can develop a finite-time singularity from smooth initial data remains one of the central open problems in nonlinear PDEs. In this talk\, I will present recent joint work with Dr. Jiajie Chen\, in which we rigorously prove finite-time blowup for the 2D Boussinesq equations and the 3D axisymmetric Euler equations with smooth initial data and smooth boundary. Our approach uses a dynamically rescaled formulation that reduces singularity formation to the long-time stability of an approximate self-similar blowup profile. A key difficulty is proving the linear stability of a numerically constructed profile. To address this\, we decompose the solution operator into a leading-order part\, which admits sharp stability estimates\, and a finite-rank perturbation\, which is controlled by a computer-assisted proof. I will also discuss recent joint work with Yixuan Wang and Changhe Yang on nonuniqueness of Leray–Hopf solutions to the unforced 3D incompressible Navier–Stokes equations. In this setting\, the viscous term introduces several new ingredients but also greatly simplifies the analysis: standard $H^1$ estimates suffice\, without the singular weights needed in the inviscid case. A central step is to establish the existence of a self-similar Leray–Hopf solution and then prove the existence of a second solution by analyzing the stability of the linearized operator around this profile and showing that it admits an unstable mode. These results highlight the fruitful interplay among analysis\, computation\, and rigorous validation in nonlinear PDEs.
URL:https://www.math.ens.psl.eu/evenement/thomas-hou/
LOCATION:ENS — amphi Galois\, 45 rue d'Ulm\, Paris\, France
CATEGORIES:Séminaire Analyse non linéaire et EDP
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Europe/Paris:20260408T093000
DTEND;TZID=Europe/Paris:20260408T103000
DTSTAMP:20260403T233438
CREATED:20260403T083819Z
LAST-MODIFIED:20260403T083820Z
UID:21217-1775640600-1775644200@www.math.ens.psl.eu
SUMMARY:Brisures de symétrie\, distributions et double quotients
DESCRIPTION:Soit G′ ⊂ G une paire de groupes et (V\, π) une représentation de G. Les problèmes de branchements consistent à étudier le comportement de la restriction π|G′ de π à G′. Dans le cas où V est un espace de Hilbert\, π est unitaire et G\, G′ sont localement compacts (par exemple des groupes de Lie)\, un théorème de Mautner implique que π|G′ se décompose (de manière unique si G′ est de type I) en intégrale directe de représentations irréductibles de G′. Lorsque π n’est pas unitaire (par exemple si π est une représentation lisse d’un groupe de Lie)\, une telle décomposition en irréductibles n’existe pas. Dans ce contexte plus général\, l’étude de π|G′ peut se faire à travers les espaces d’opérateurs de brisure de symétrie\, c’est-à-dire les espaces Hom_G′(π\, τ) où τ parcourt une classe appropriée de représentations de G. Dans le cas où G et G′ sont des groupes de Lie réductifs réels (par exemple (G\, G′) = (GL(n+1\, R)\, GL(n\, R)))\, une classe de représentations raisonnable de G et G′ est donnée par les représentations de leur série principale\, représentations obtenues par induction parabolique et donc géométriquement à partir de fibrés vectoriels homogènes. Dans cet exposé\, nous verrons à travers des exemples comment et pourquoi les distributions\, couplées à un certain double quotient\, fournissent un angle d’attaque redoutable pour l’étude des problèmes de branchement des groupes de Lie réductifs réels. \n\n\n\n.
URL:https://www.math.ens.psl.eu/evenement/brisures-de-symetrie-distributions-et-double-quotients/
LOCATION:Salle W
CATEGORIES:Colloquium doctorant
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Europe/Paris:20260408T110000
DTEND;TZID=Europe/Paris:20260408T120000
DTSTAMP:20260403T233438
CREATED:20260402T124328Z
LAST-MODIFIED:20260402T124444Z
UID:21211-1775646000-1775649600@www.math.ens.psl.eu
SUMMARY:Basile Morando\, raconte-nous les groupes de Neretin !
DESCRIPTION:Les groupes de Neretin ont été définis par Yuri Neretin au début des années 90\, à l’origine comme analogues p-adiques du groupe des difféomorphismes du cercle. Depuis la preuve de leur simplicité par Kapoudjian en 1999\, ces groupes (localement compacts et totalement discontinus) suscitent un intérêt croissant: ils présentent de remarquables propriétés qui contrastent avec celles des groupes localement compacts simples connexes. Dans cet exposé\, on s’intéressera notamment au fait qu’ils n’admettent aucun réseau\, ainsi qu’aux propriétés remarquables de leurs représentations unitaires.
URL:https://www.math.ens.psl.eu/evenement/basile-morando-raconte-nous-les-groupes-de-neretin/
LOCATION:Salle W toits du DMA
CATEGORIES:Algèbre et géométrie,Séminaire Raconte-moi
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Europe/Paris:20260408T140000
DTEND;TZID=Europe/Paris:20260408T170000
DTSTAMP:20260403T233438
CREATED:20260403T082003Z
LAST-MODIFIED:20260403T082112Z
UID:21215-1775656800-1775667600@www.math.ens.psl.eu
SUMMARY:Un après-midi de théorie des groupes - Adrien Boyer\, Julien Marché\, Greg Patchell
DESCRIPTION:14:00-14:45 Adrien Boyer (IMJ-PRG): Property RD and Boundary Representations for A2 Buildings  \n\n\n\n15:00-15:45 Julien Marché (ENS – PSL): Action of endomorphisms of free groups on their SL_2-character varieties  \n\n\n\n16:15-17:00 Greg Patchell (University of Oxford): Selfless Inclusions of C*-Algebras and Quantum Groups \n\n\n\n \n\n\n\nAbstracts: \n\n\n\nGreg Patchell: Selfless Inclusions of C*-Algebras and Quantum Groups \n\n\n\nRecently\, strong asymptotic freeness\, or selflessness\, in C-algebras has emerged as a powerful technique to prove important regularity properties including simplicity\, unique trace\, stable rank 1\, and strict comparison. In particular\, in Fall 2024\, Amrutam\, Gao\, Kunnwalkam Elayavalli\, and I showed that the reduced group C-algebras of all hyperbolic groups with trivial finite radical are selfless\, which resolved the open problem of strict comparison for the reduced group C-algebra of the free group on two generators. Since then\, our result has been expanded to include a much larger class of groups. Work has also begun on isolating selflessness for C-algebras not arising from groups\, including the result of Hayes\, Kunnawalkam Elayavalli\, and Robert on selflessness of the reduced free product of a large class of C-algebras (see also Flores-Klisse-Ó Cobhthaigh-Pagliero). I will introduce the general notion of a selfless inclusion of C-algebras\, with which we will see the selflessness of the reduced unitary compact matrix quantum groups. This work is joint with Ben Hayes\, Srivatsav Kunnawalkam Elayavalli\, and Leonel Robert. \n\n\n\n \n\n\n\nAdrien Boyer: Property RD and Boundary Representations for A2 Buildings \n\n\n\nI will discuss an approach based on boundary representations to prove property RD for discrete groups acting properly and cocompactly on affine buildings of type A2. This result is due to Robertson\, Ramagge\, and Steger in the late 1990s. I will emphasize geometric arguments involving the Furstenberg boundary that can be used to establish property RD\, in particular the notion of “foldings” or “confluences\,” as suggested by V. Kaimanovich. Along the way\, I will also mention a conjecture of Robertson\, Ramagge\, and Steger concerning the optimal bound\, and propose a possible approach toward resolving it. If time permits\, I will also explain what happens in the C2 case. This is joint work with Thang Nguyen. \n\n\n\n \n\n\n\nJulien Marché: Action of endomorphisms of free groups on their SL_2-character varieties. \n\n\n\nLet phi : F_n->F_n be an endomorphism and let phi^* denote its action on the character variety X_n=Hom(F_n\,SL_2(C))/SL_2(C). Cantat-Gelander-Souto raised the question whether phi^* is an automorphism of the affine variety X_n if and only if phi is an automorphism of F_n. I will describe work in progress which relates directly this question to the action of endomorphisms on the outer space CV_n through a compactification of X_n with special valuations.
URL:https://www.math.ens.psl.eu/evenement/un-apres-midi-de-theorie-des-groupes-adrien-boyer-julien-marche-greg-patchell/
LOCATION:Salle W
CATEGORIES:Séminaire de théorie des groupes à l’ENS
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Europe/Paris:20260409T124500
DTEND;TZID=Europe/Paris:20260409T134500
DTSTAMP:20260403T233438
CREATED:20260326T102406Z
LAST-MODIFIED:20260326T102534Z
UID:21172-1775738700-1775742300@www.math.ens.psl.eu
SUMMARY:ENS-Data Science colloquium - Michael Chertkov : Samples That Cooperate\, Samples That Remember: Two Exactly Solvable Bridge Diffusions
DESCRIPTION:Diffusion-based generative models treat samples as independent and memoryless. I will show that relaxing each assumption leads to rich\, exactly solvable physics — with no neural networks anywhere.Giving samples a present — coupling them through their evolving mean field — produces a McKean–Vlasov optimal transport problem whose self-consistent guidance is provably the linear interpolant between endpoint means\, for arbitrary distributions and any interaction schedule; applied to building-fleet demand response\, this saves 20%+ in actuation energy.Giving samples a past produces a continual-learning agent whose memory is a Bridge Diffusion and whose forgetting — arising from a single lossy temporal coarse-graining step — obeys a universal linear capacity law with a Shannon-like constant.Both constructions live in the world of Riccati equations\, hyperbolic functions\, and mixture linear algebra; the physics of the bridge — not the expressivity of a network — controls what is achievable. \n\n\n\n  \n\n\n\nThese seminars are being made possible through the support of the CFM-ENS Chair « Modèles et Sciences des Données ». \n\n\n\nThe organizers: Giulio Biroli\, Alex Cayco Gajic\, Bruno Loureiro\, Stéphane Mallat\, Gabriel Peyré.
URL:https://www.math.ens.psl.eu/evenement/ens-data-science-colloquium-michael-chertkov-samples-that-cooperate-samples-that-remember-two-exactly-solvable-bridge-diffusions/
LOCATION:ENS Salle Dussane
CATEGORIES:ENS-Data Science colloquium
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Europe/Paris:20260422T131500
DTEND;TZID=Europe/Paris:20260422T141500
DTSTAMP:20260403T233438
CREATED:20260401T122700Z
LAST-MODIFIED:20260401T122726Z
UID:21201-1776863700-1776867300@www.math.ens.psl.eu
SUMMARY:Marco Mazzucchelli
DESCRIPTION:Séminaires des Mathématiques
URL:https://www.math.ens.psl.eu/evenement/marco-mazzucchelli/
LOCATION:ENS — amphi Galois\, 45 rue d'Ulm\, Paris\, France
CATEGORIES:ANNÉE 2025-2026,Prochaine séance,Séminaire Des mathématiques
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Europe/Paris:20260506T131500
DTEND;TZID=Europe/Paris:20260506T141500
DTSTAMP:20260403T233438
CREATED:20260401T122545Z
LAST-MODIFIED:20260401T122546Z
UID:21204-1778073300-1778076900@www.math.ens.psl.eu
SUMMARY:Céline Lévy-Leduc
DESCRIPTION:Séminaires des Mathématiques
URL:https://www.math.ens.psl.eu/evenement/celine-levy-leduc/
LOCATION:ENS — amphi Galois\, 45 rue d'Ulm\, Paris\, France
CATEGORIES:ANNÉE 2025-2026,Séances suivantes,Séminaire Des mathématiques
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Europe/Paris:20260519T093000
DTEND;TZID=Europe/Paris:20260519T123000
DTSTAMP:20260403T233438
CREATED:20251018T115511Z
LAST-MODIFIED:20260113T203313Z
UID:20144-1779183000-1779193800@www.math.ens.psl.eu
SUMMARY:Vlad Vicol
DESCRIPTION:
URL:https://www.math.ens.psl.eu/evenement/vlad-vicol/
LOCATION:Jussieu —  salle 15-16-309\, 4 Place Jussieu\, Paris\, 75005\, France
CATEGORIES:Séminaire Analyse non linéaire et EDP
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Europe/Paris:20260520T131500
DTEND;TZID=Europe/Paris:20260520T141500
DTSTAMP:20260403T233438
CREATED:20260401T122300Z
LAST-MODIFIED:20260401T122839Z
UID:21207-1779282900-1779286500@www.math.ens.psl.eu
SUMMARY:Rémi Coulon
DESCRIPTION:Séminaires des Mathématiques
URL:https://www.math.ens.psl.eu/evenement/remi-coulon/
LOCATION:ENS — amphi Galois\, 45 rue d'Ulm\, Paris\, France
CATEGORIES:ANNÉE 2025-2026,Séances suivantes,Séminaire Des mathématiques
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Europe/Paris:20260609T093000
DTEND;TZID=Europe/Paris:20260609T123000
DTSTAMP:20260403T233438
CREATED:20251018T115549Z
LAST-MODIFIED:20260113T203203Z
UID:20146-1780997400-1781008200@www.math.ens.psl.eu
SUMMARY:Hélène Mathis
DESCRIPTION:
URL:https://www.math.ens.psl.eu/evenement/helene-mathis/
LOCATION:Salle W – ENS PSL\, 45 rue d'Ulm\, Paris\, 75005\, France
CATEGORIES:Séminaire Analyse non linéaire et EDP
END:VEVENT
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