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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
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DTSTART:20210328T010000
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DTSTART:20211031T010000
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BEGIN:VEVENT
DTSTART;TZID=Europe/Paris:20220607T160000
DTEND;TZID=Europe/Paris:20220607T173000
DTSTAMP:20260418T161444
CREATED:20220603T082812Z
LAST-MODIFIED:20220603T082812Z
UID:15632-1654617600-1654623000@www.math.ens.psl.eu
SUMMARY:Cercles isométriques mais contractiles dans les cônes asymptotiques des groupes
DESCRIPTION:La contractilité de tous les cercles dans les cônes asymptotiques d’un groupe G de type fini implique que G est de présentation finie avec fonction de Dehn au plus polynomiale.  Le distorsion métrique de tous ces cercles est une propriété plus forte qui implique que G est fortement raccourci (“strongly shortcut”).  La propriété fortement raccourci est satisfaite par diverses familles de groupes de courbure négative ou nulle\, notamment les groupes hyperboliques\, CAT(0)\, Helly\, et systoliques\, mais elle est aussi satisfaite par le groupe de Heisenberg discret.\n    Je discuterai d’un récent travail en commun avec Cashen et Woodhouse où on a montré qu’une famille infinie de groupes flocon de\nneige (“snowflake groups”) ont des cônes asymptotiques simplement connexes mais des graphes de Cayley qui ne sont pas fortement\nraccourcis.  Ce sont les premiers exemples de groupes qui ont des cônes asymptotiques dans lesquels il existe des cercles isométriques\nmais contractiles.
URL:https://www.math.ens.psl.eu/evenement/cercles-isometriques-mais-contractiles-dans-les-cones-asymptotiques-des-groupes/
LOCATION:salle 1016 Sophie Germain
CATEGORIES:Théorie des Modèles et Groupes
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Europe/Paris:20220531T160000
DTEND;TZID=Europe/Paris:20220531T170000
DTSTAMP:20260418T161444
CREATED:20220502T091657Z
LAST-MODIFIED:20220502T091657Z
UID:15552-1654012800-1654016400@www.math.ens.psl.eu
SUMMARY:Le théorème du corps gauche de Zilber / Zilber's Skew-Field Theorem (joint with Frank Wagner)
DESCRIPTION:Le théorème du corps est l’observation qu’un groupe de rang de Morley fini connexe\, résoluble\, et non nilpotent\, interprète un corps infini. Par d’autres résultats classiques\, le corps est commutatif et même algébriquement clos.\nLe théorème du corps est souvent vu comme corollaire du «théorème d’engendrement par des indécomposables» mais c’est une erreur car il en est indépendant. Il a quelques variantes\, des théorèmes de linéarisation d’actions de groupes.\nJe donnerai un énoncé qui généralise naturellement tous les résultats «à la Zilber». C’est un résultat de linéarisation de bimodules\, dans un contexte plus général que les théories de rang de Morley fini. En général on interprète un corps gauche.\nPrérequis : notion de définissabilité ; «lemme de Schur» en théorie des représentations (l’anneau des endomorphismes qui commutent avec une représentation irréductible est en fait un corps gauche). \nZilber’s Field Theorem ZFT is the observation that a connected\, soluble\, non-nilpotent group of finite Morley rank interprets an infinite field. By other classical results\, the field is commutative indeed\, and even algebraically closed.\nThe ZFT is often seen as a corollary to Zilber’s `indecomposable generation theorem’; but it actually is independent from it. The ZFT has a couple of variants\, linearisation results for definable group actions.\nI shall give a theorem which generalises naturally all results `à la Zilber’. It is a tool that can linearise bimodule actions\, in a broader context than theories of finite Morley rank. In general it produces a definable skew-field.\nPrerequisites: definable sets; `Schur’s lemma’ from representation theory (the ring of endomorphisms commuting with an irreducible representation\, actually is a skew-field).
URL:https://www.math.ens.psl.eu/evenement/le-theoreme-du-corps-gauche-de-zilber-zilbers-skew-field-theorem-joint-with-frank-wagner/
LOCATION:Sophie Germain salle 1016.
CATEGORIES:Théorie des Modèles et Groupes
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Europe/Paris:20220513T160000
DTEND;TZID=Europe/Paris:20220513T173000
DTSTAMP:20260418T161444
CREATED:20220503T102922Z
LAST-MODIFIED:20220503T102922Z
UID:15562-1652457600-1652463000@www.math.ens.psl.eu
SUMMARY:Sharp o-minimality: towards an arithmetically tame geometry
DESCRIPTION:Over the last 15 years a remarkable link between o-minimality and algebraic/arithmetic geometry has been unfolding following the discovery of Pila-Wilkie’s counting theorem and its applications around unlikely intersections\, functional transcendence etc. While the counting theorem is nearly optimal in general\, Wilkie has conjectured a much sharper form in the structure R_exp. There is a folklore expectation that such sharper bounds should hold in structures « coming from geometry »\, but for lack of a general formalism explicit conjectures have been made only for specific structures.\nI will describe a refinement of the standard o-minimality theory aimed at capturing the finer « arithmetic tameness » that we expect to see in structures coming from geometry. After presenting the general framework I will discuss my result with Vorobjov showing that the restricted Pfaffian structure is sharply o-minimal\, and how this was used in our recent work with Novikov and Zack to prove Wilkie’s conjecture for the restricted Pfaffian structure and for Wilkie’s original case of R_exp. I will also discuss some conjectures on the construction of larger sharply o-minimal structures\, and some partial results in this direction. Finally I will explain the crucial role played by these results in my recent work with Schmidt and Yafaev on Galois orbit lower bounds for CM points in general Shimura varieties\, and subsequently in the recent resolution of general André-Oort conjecture by Pila-Shankar-Tsimerman-(Esnault-Groechenig).
URL:https://www.math.ens.psl.eu/evenement/sharp-o-minimality-towards-an-arithmetically-tame-geometry/
LOCATION:Salle W (ENS) et Zoom
CATEGORIES:Séminaire Géométrie et théorie des modèles
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Europe/Paris:20220513T141500
DTEND;TZID=Europe/Paris:20220513T154500
DTSTAMP:20260418T161444
CREATED:20220421T120028Z
LAST-MODIFIED:20220503T103029Z
UID:15542-1652451300-1652456700@www.math.ens.psl.eu
SUMMARY:Skew-invariant curves and algebraic independence
DESCRIPTION:A σ-variety over a difference field (K\,σ) is a pair (X\,φ) consisting of an algebraic variety X over K and φ:X → X^σ is a regular map from X to its transform Xσ under σ. A subvariety Y ⊆ X is skew-invariant if φ(Y) ⊆ Y^σ. In earlier work with Alice Medvedev we gave a procedure to describe skew-invariant varieties of σ-varieties of the form (𝔸^n\,φ) where φ(x_1\,…\,x_n) = (P_1(x_1)\,…\,P_n(x_n)). The most important case\, from which the others may be deduced\, is that of n = 2. In the present work we give a sharper description of the skew-invariant curves in the case where P_2 = P_1^τ for some other automorphism of K which commutes with σ. Specifically\, if P in K[x] is a polynomial of degree greater than one which is not eventually skew-conjugate to a monomial or ± Chebyshev (i.e. P is “nonexceptional”) then skew-invariant curves in (𝔸^2\,(P\,P^τ)) are horizontal\, vertical\, or skew-twists: described by equations of the form y = α^{σ^n} ∘ P^{σ^{n-1}} ∘ ⋅⋅⋅ ∘ P^σ ∘ P(x) or x = β^{σ{-1}}∘ P^{τ σ^{-n-2}}∘ P^{τ σ^{-n-3}}∘ ⋅⋅⋅ ∘ P^τ(y) where P = α ∘ β and P^τ = α^{σ^{n+1}}∘ β^{σ^n}} for some integer n.
URL:https://www.math.ens.psl.eu/evenement/skew-invariant-curves-and-algebraic-independence/
CATEGORIES:Séminaire Géométrie et théorie des modèles
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Europe/Paris:20220513T110000
DTEND;TZID=Europe/Paris:20220513T123000
DTSTAMP:20260418T161444
CREATED:20220421T115851Z
LAST-MODIFIED:20220503T103102Z
UID:15539-1652439600-1652445000@www.math.ens.psl.eu
SUMMARY:Complexity of l-adic sheaves
DESCRIPTION:To a complex of l-adic sheaves on a quasi-projective variety one associate an integer\, its complexity. The main result on the complexity is that it is continuous with tensor product\, pullback and pushforward\, providing effective version of the constructibility theorems in l-adic cohomology. Another key feature is that the complexity bounds the dimensions of the cohomology groups of the complex. This can be used to prove equidistribution results for exponential sums over finite fields. This is due to Will Sawin\, written up in collaboration with Javier Fresán and Emmanuel Kowalski.
URL:https://www.math.ens.psl.eu/evenement/complexity-of-l-adic-sheaves/
CATEGORIES:Séminaire Géométrie et théorie des modèles
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Europe/Paris:20220510T160000
DTEND;TZID=Europe/Paris:20220510T173000
DTSTAMP:20260418T161444
CREATED:20220502T091359Z
LAST-MODIFIED:20220502T115516Z
UID:15549-1652198400-1652203800@www.math.ens.psl.eu
SUMMARY:Existential theories of henselian fields\, parameters welcome
DESCRIPTION:The first-order theories of local fields of positive characteristic\, i.e. fields of Laurent series over finite fields\, are far less well understood than their characteristic zero analogues: the fields of real\, complex and p-adic numbers. On the other hand\, the existential theory of an equicharacteristic henselian valued field in the language of valued fields is controlled by the existential theory of its residue field. One is decidable if and only if the other is decidable. When we add a parameter to the language\, things get more complicated. Denef and Schoutens gave an algorithm\, assuming resolution of singularities\, to decide the existential theory of rings like Fp[[t]]\, with the parameter t in the language. I will discuss their algorithm and present a new result (from ongoing work\, with Dittmann and Fehm) that weakens the hypothesis to a form of local uniformization\, and which works in greater generality.
URL:https://www.math.ens.psl.eu/evenement/tba-12/
LOCATION:Sophie Germain salle 1016
CATEGORIES:Théorie des Modèles et Groupes
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Europe/Paris:20220420T110000
DTEND;TZID=Europe/Paris:20220420T120000
DTSTAMP:20260418T161444
CREATED:20220416T145512Z
LAST-MODIFIED:20220416T145512Z
UID:15535-1650452400-1650456000@www.math.ens.psl.eu
SUMMARY:Olivier de Gaay Fortman\, raconte-moi la conjecture de Hodge entière !
DESCRIPTION:La conjecture de Hodge reste une conjecture largement ouverte et mystérieuse. Dans cet exposé je parlerai d’un énoncé encore plus fort : la « Conjecture de Hodge Entière ». Bien que fausse en général\, il est\nimportant de se demander pour quel type de variétés complexes projectives elle est vraie. Je la prouverai pour les classes de homologie de degré deux sur la jacobienne d’une courbe. Enfin\, je parlerai de son analogue pour les variétés algébriques réelles: la « Conjecture de Hodge Entière Réelle ».
URL:https://www.math.ens.psl.eu/evenement/olivier-de-gaay-fortman-raconte-moi-la-conjecture-de-hodge-entiere/
LOCATION:En salle W au DMA\, ou sur Zoom
CATEGORIES:Algèbre et géométrie,Séminaire Raconte-moi
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Europe/Paris:20220419T160000
DTEND;TZID=Europe/Paris:20220419T173000
DTSTAMP:20260418T161444
CREATED:20220404T121410Z
LAST-MODIFIED:20220415T110132Z
UID:15497-1650384000-1650389400@www.math.ens.psl.eu
SUMMARY:Metric valued fields in continuous logic
DESCRIPTION:By work of Itaï Ben Yaacov complete valued fields with value groups embedded in the real numbers can be viewed as metric structures in continuous logic. For technical reasons one has to consider the projective line over such a field rather than the field itself.\nIn this talk we introduce the above setting and give a classification of the complete theories of metric valued fields in equicharacteristic 0 in terms of their residue field and value group. This can also be seen as an approximate Ax-Kochen-Ershov principle. If time permits\, as a second result we give a negative answer to a question of Ben Yaacov on the existence of a model companion for metric valued fields enriched with an isometric automorphism. This is joint work with Martin Hils.
URL:https://www.math.ens.psl.eu/evenement/metric-valued-fields-in-continuous-logic/
LOCATION:Sophie Germain salle 1016.
CATEGORIES:Théorie des Modèles et Groupes
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Europe/Paris:20220405T160000
DTEND;TZID=Europe/Paris:20220405T173000
DTSTAMP:20260418T161444
CREATED:20220323T200336Z
LAST-MODIFIED:20220323T200552Z
UID:15480-1649174400-1649179800@www.math.ens.psl.eu
SUMMARY:Quasi-groupes de Frobenius dimensionnels
DESCRIPTION:Dans cet exposé\, nous présenterons une généralisation des groupes de Frobenius : les quasi-groupes de Frobenius. On dit qu’une paire de groupes C < G est un quasi-groupe de Frobenius si C est d’indice fini dans son normalisateur (dans G) et s’il satisfait la propriété TI\, i.e\, deux conjugués distincts de C s’intersectent trivialement.\nDu point de vue de la théorie des modèles\, nous travaillerons dans un contexte où l’existence d’une bonne notion de dimension (finie) sur les ensembles définissables est assurée (ce qui englobe les univers rangés et les structures o-minimales).\nEn s’inscrivant dans le prolongement des travaux classiques de l’école de Bachmann et d’un article plus récent de A. Deloro et J. Wiscons\, nous examinerons dans quelle mesure l’étude des géométries d’incidence induites par les involutions au sein des quasi-groupes de Frobenius permet d’identifier dans un cadre dimensionnel les groupes classiques GA_1(C)\, PGL_2(C) et SO_3(R).
URL:https://www.math.ens.psl.eu/evenement/quasi-groupes-de-frobenius-dimensionnels/
LOCATION:Sophie Germain salle 1016.
CATEGORIES:Théorie des Modèles et Groupes
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Europe/Paris:20220405T141500
DTEND;TZID=Europe/Paris:20220405T174500
DTSTAMP:20260418T161444
CREATED:20220329T170123Z
LAST-MODIFIED:20220329T170312Z
UID:15493-1649168100-1649180700@www.math.ens.psl.eu
SUMMARY:Piecewise Interpretable Hilbert Spaces (II)
DESCRIPTION:We continue the discussion of piecewise interpretable Hilbert spaces from the Monday seminar. We will prove the main structure theorem of `Piecewise Interpretable Hilbert Spaces’ (C.\, Hrushovski) which analyses a scattered piecewise interpretable Hilbert space into asymptotically free subspaces. We will clarify the model theoretic content of this theorem\, highlighting the roles of one-basedness and strong minimality. We will also study its representation theoretic content\, establishing a connection with induced represetnations. We will see that this theorem generalises a theorem of Tsankov about unitary representations of oligomorphic groups. This is joint work with Ehud Hrushovski.
URL:https://www.math.ens.psl.eu/evenement/piecewise-interpretable-hilbert-spaces-ii/
LOCATION:Sophie Germain salle 1016.
CATEGORIES:Théorie des Modèles et Groupes
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Europe/Paris:20220322T160000
DTEND;TZID=Europe/Paris:20220322T173000
DTSTAMP:20260418T161444
CREATED:20220317T152124Z
LAST-MODIFIED:20220317T152139Z
UID:15444-1647964800-1647970200@www.math.ens.psl.eu
SUMMARY:Lie groups definable in o-minimal theories
DESCRIPTION:In this talk we will work out a complete characterization of which Lie groups admit a “definable copy”. This is\, characterize for which Lie groups G one can find a group H definable in an o-minimal expansion of the real field\, and such that G and H are isomorphic.\nWhen the answer is positive\, the definable copy H that we find is definable in the language of exponential ordered fields\, and it is such that any Lie automorphism of H is definable.
URL:https://www.math.ens.psl.eu/evenement/lie-groups-definable-in-o-minimal-theories/
LOCATION:Sophie Germain salle 1016.
CATEGORIES:Théorie des Modèles et Groupes
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Europe/Paris:20220318T154500
DTEND;TZID=Europe/Paris:20220318T171500
DTSTAMP:20260418T161444
CREATED:20220318T144518Z
LAST-MODIFIED:20220311T152909Z
UID:15394-1647618300-1647623700@www.math.ens.psl.eu
SUMMARY:Tameness beyond o-minimality (in expansions of the real ordered additive group)
DESCRIPTION:In his influential paper “Tameness in expansions of the real field” from the early 2000s\, Chris Miller wrote: \n“ What might it mean for a first-order expansion of the field of real numbers to be tame or well behaved? In recent years\, much attention has been paid by model theorists and real-analytic geometers to the o-minimal setting: expansions of the real field in which every definable set has finitely many connected components. But there are expansions of the real field that define sets with infinitely many connected components\, yet are tame in some well-defined sense […]. The analysis of such structures often requires a mixture of model-theoretic\, analytic-geometric and descriptive set-theoretic techniques. An underlying idea is that first-order definability\, in combination with the field structure\, can be used as a tool for determining how complicated is a given set of real numbers.” \nMuch progress has been made since then\, and in this talk I will discuss an updated account of this research program. I will consider this program in the larger generality of expansions of the real ordered additive group (rather than just in expansions of the real field as envisioned by Miller). In particular\, I will mention in this context recent joint work with Erik Walsberg\, in which we produce an interesting tetrachotomy for such expansions.
URL:https://www.math.ens.psl.eu/evenement/tameness-beyond-o-minimality-in-expansions-of-the-real-ordered-additive-group/
LOCATION:Zoom
CATEGORIES:Séminaire Géométrie et théorie des modèles
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Europe/Paris:20220318T140000
DTEND;TZID=Europe/Paris:20220318T153000
DTSTAMP:20260418T161444
CREATED:20220311T152633Z
LAST-MODIFIED:20220311T152633Z
UID:15421-1647612000-1647617400@www.math.ens.psl.eu
SUMMARY:Interdefinability and compatibility in certain o-minimal expansions of the real field
DESCRIPTION:Let us say that a real function f is o-minimal if the expansion (R\,f) of the real field by f is o-minimal. A function g is definable from f if g is definable in (R\,f). Two o-minimal functions are compatible if there exists an o-minimal expansion M of the real field in which they are both definable. I will discuss the o-minimality\, the interdefinability and the compatibility of two special functions\, Euler’s Gamma and Riemann’s Zeta\, restricted to the reals. If time allows it\, I will present a general technique for establishing whether a function is definable or not in a given o-minimal expansion of the reals. Joint work with J.-P. Rolin and P. Speissegger.
URL:https://www.math.ens.psl.eu/evenement/interdefinability-and-compatibility-in-certain-o-minimal-expansions-of-the-real-field/
LOCATION:Zoom
CATEGORIES:Séminaire Géométrie et théorie des modèles
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Europe/Paris:20220315T160000
DTEND;TZID=Europe/Paris:20220315T173000
DTSTAMP:20260418T161444
CREATED:20220309T160534Z
LAST-MODIFIED:20220309T160950Z
UID:15402-1647360000-1647365400@www.math.ens.psl.eu
SUMMARY:Curve-excluding fields
DESCRIPTION:Consider the class of fields with Char(K)=0 and x^4+y^4=1 has only 4 solutions in K\, we show that this class has a model companion\, which we denote by curve-excluding fields. Curve-excluding fields provides (counter)examples to various questions. Model theoretically\, they are model complete and TP_2. Field theoretically\, they are not large and unbounded. We will discuss other aspects such as decidability of such fields. This is joint work with Will Johnson and Erik Walsberg.
URL:https://www.math.ens.psl.eu/evenement/curve-excluding-fields-2/
LOCATION:salle 1016 Sophie Germain
CATEGORIES:Théorie des Modèles et Groupes
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Europe/Paris:20220315T140000
DTEND;TZID=Europe/Paris:20220315T170000
DTSTAMP:20260418T161444
CREATED:20220305T170139Z
LAST-MODIFIED:20220305T170529Z
UID:15335-1647352800-1647363600@www.math.ens.psl.eu
SUMMARY:Un après-midi de théorie des groupes
DESCRIPTION:Le séminaire sera dans salle W et retransmis sur Zoom : \nZOOM: https://us02web.zoom.us/j/82070470538\nID: 820 7047 0538\nMot de passe:\nG est un Graphe de Cayley du groupe libre à 107 générateurs. Quel est\nle degré de ce graphe? Tapez le numéro à trois chiffres comme un mot\nde passe. \n14.00 – 14.45 Marcin Sabok  (McGill University)\, « Hyperfiniteness at\nhyperbolic boundries » \n15.00 – 15.45 Juan Paucar (Jussieu)\, « Coarse embeddings between locally\ncompact groups and quantitative measured equivalence » \n16.00 – 16.45 Josh Frisch (ENS)\, « Characteristic Measures and Minimal\nSubdynamics » \nVous pourrez trouver les résumés sur le site du séminaire:\nhttps://sites.google.com/site/annaerschler/grseminar
URL:https://www.math.ens.psl.eu/evenement/un-apres-midi-de-theorie-des-groupes/
LOCATION:14:00-17:00 Salle W
CATEGORIES:Séminaire de théorie des groupes à l’ENS
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Europe/Paris:20220309T110000
DTEND;TZID=Europe/Paris:20220309T120000
DTSTAMP:20260418T161444
CREATED:20220218T132131Z
LAST-MODIFIED:20220218T132131Z
UID:15310-1646823600-1646827200@www.math.ens.psl.eu
SUMMARY:Najib Idrissi\, raconte-moi les opérades !
DESCRIPTION:Les opérades sont des objets qui gouvernent des catégories d’algèbres au sens large — par exemple\, les algèbres associatives\, les algèbres commutatives\, ou les algèbres de Lie — qui sont habituellement définies par « opérations génératrices et relations ». Le but de cet exposé est d’introduire la théorie des opérades avec des exemples\, et en particulier l’exemple fondateur des opérades des petits disques. J’expliquerai comment les opérades des petits disques permettent d’obtenir des invariants des variétés de deux façons duales : le calcul des plongements et l’homologie de factorisation.
URL:https://www.math.ens.psl.eu/evenement/najib-idrissi-raconte-moi-les-operades/
LOCATION:En salle W au DMA\, ou sur Zoom
CATEGORIES:Algèbre et géométrie,Séminaire Raconte-moi
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Europe/Paris:20220301T160000
DTEND;TZID=Europe/Paris:20220301T173000
DTSTAMP:20260418T161444
CREATED:20220223T142159Z
LAST-MODIFIED:20220309T160937Z
UID:15319-1646150400-1646155800@www.math.ens.psl.eu
SUMMARY:Existentially closed measure-preserving actions of free groups
DESCRIPTION:I will discuss a joint work with Alexander Berenstein and Ward Henson\, in which we show that the theory of probability algebras with two automorphisms has a model completion\, which moreover has quantifier elimination and is stable. We also exhibit two non-isomorphic (but approximately isomorphic) models of the model completion.\nMore generally\, we give a sufficient set of conditions for the axiomatizability (in continuous logic) of the existentially closed actions of a free group on a separably categorical\, stable structure.\nI will also mention a number of open questions.
URL:https://www.math.ens.psl.eu/evenement/existentially-closed-measure-preserving-actions-of-free-groups/
LOCATION:Sophie Germain salle 1016.
CATEGORIES:Théorie des Modèles et Groupes
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Europe/Paris:20220222T160000
DTEND;TZID=Europe/Paris:20220222T173000
DTSTAMP:20260418T161444
CREATED:20220214T184113Z
LAST-MODIFIED:20220214T184113Z
UID:15214-1645545600-1645551000@www.math.ens.psl.eu
SUMMARY:NIPn fields part 2: random hypergraphs and NIPn CHIPS transfer
DESCRIPTION:A core question in the model theory of fields is to understand how combinatorial patterns and algebraic properties interact. The study of NIPn fields\, which can’t express the edge relation of random n-hypergraph\, is linked to henselianity. In this talk\, we use Chernikov and Hils conditions to obtain transfer in some situations\, that is\, under some algebraic assumptions\, it is enough to know that the residue field of a henselian valued field is NIPn in order to known that it is itself NIPn\, and we discuss consequences on hypothetical strictly NIPn fields.
URL:https://www.math.ens.psl.eu/evenement/nipn-fields-part-2-random-hypergraphs-and-nipn-chips-transfer/
LOCATION:salle 1016 Sophie Germain
CATEGORIES:Théorie des Modèles et Groupes
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Europe/Paris:20220218T154500
DTEND;TZID=Europe/Paris:20220218T171500
DTSTAMP:20260418T161444
CREATED:20220203T145355Z
LAST-MODIFIED:20220211T161457Z
UID:15158-1645199100-1645204500@www.math.ens.psl.eu
SUMMARY:Not Pfaffian
DESCRIPTION:This talk describes the connection between /strong minimality/ of the differential equation satisfied by an complex analytic function and the real and imaginary parts of the function being /Pfaffian/. The talk will not assume the audience knows these notions previously\, and will attempt to motivate why each of them are important notions in various areas. The connection we give\, combined with a theorem of Freitag and Scanlon (2017) provides the answer to a question of Binyamini and Novikov (2017). We also answer a question of Bianconi (2016). We give what seem to be the first examples of functions which are definable in o-minimal expansions of the reals and are differentially algebraic\, but not Pfaffian.
URL:https://www.math.ens.psl.eu/evenement/not-pfaffian/
LOCATION:Zoom
CATEGORIES:Séminaire Géométrie et théorie des modèles
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Europe/Paris:20220218T140000
DTEND;TZID=Europe/Paris:20220218T153000
DTSTAMP:20260418T161444
CREATED:20220204T103217Z
LAST-MODIFIED:20220204T103815Z
UID:15163-1645192800-1645198200@www.math.ens.psl.eu
SUMMARY:The Kemperman inverse 	problem
DESCRIPTION:Let G be a connected locally compact group with a left Haar measure μ\, and let A\,B ⊆ G be nonempty and compact. Assume further that G is unimodular\, i.e.\, μ is also the right Haar measure; this holds\, e.g.\, when G is compact\, a nilpotent Lie group\, or a semisimple Lie group. In 1964\, Kemperman showed that \nμ(AB) ≥ min {μ(A)+μ(B)\, μ(G)} .\nThe Kemperman inverse problem (proposed by Griesmer\, Kemperman\, and Tao) asks when the equality happens or nearly happens. I will discuss the recent solution of this problem\, highlighting the connections to model theory. (Joint with Jinpeng An\, Yifan Jing\, and Ruixiang Zhang).
URL:https://www.math.ens.psl.eu/evenement/the-kemperman-inverse-problem/
LOCATION:Zoom
CATEGORIES:Séminaire Géométrie et théorie des modèles
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Europe/Paris:20220216T110000
DTEND;TZID=Europe/Paris:20220216T120000
DTSTAMP:20260418T161444
CREATED:20220214T103226Z
LAST-MODIFIED:20220214T103301Z
UID:15204-1645009200-1645012800@www.math.ens.psl.eu
SUMMARY:Léonard Pille-Schneider\, raconte-moi les espaces hybrides !
DESCRIPTION:Soit X=(X_t) une famille de variétés algébriques complexes paramétrée par le disque épointé\, dont les équations ont une singularité méromorphe en t=0. Le but de cet exposé est d’expliquer comment associer à cette famille un espace dit hybride\, permettant de voir les variétés complexes X_t dégénérer vers l’espace analytique non-archimédien obtenu en interprétant X comme une variété algébrique sur le corps des séries de Laurent. Je donnerai aussi des applications géométriques de cette construction.
URL:https://www.math.ens.psl.eu/evenement/leonard-pille-schneider-raconte-moi-les-espaces-hybrides/
LOCATION:En salle W au DMA\, ou sur Zoom
CATEGORIES:Séminaire Raconte-moi
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Europe/Paris:20220215T160000
DTEND;TZID=Europe/Paris:20220215T173000
DTSTAMP:20260418T161444
CREATED:20220207T145840Z
LAST-MODIFIED:20220211T161554Z
UID:15168-1644940800-1644946200@www.math.ens.psl.eu
SUMMARY:Groups definable in partial differential fields with an automorphism
DESCRIPTION:This is a joint work with Ronald Bustamante Medina and Zoé Chatzidakis.\nIn this talk we are interested in differential and difference fields from the model-theoretic point of view. A differential field is a field with a set of commuting derivations and a difference-differential field is a differential field equipped with an automorphism which commutes with the derivations.\nCassidy studied definable groups in differentially closed fields\, in particular she studied Zariski dense definable subgroups of simple algebraic groups and showed that they are isomorphic to the rational points of an algebraic group over some definable field. In this talk we study groups definable in existentially closed difference-differential fields. In particular\, we study Zariski dense definable subgroups of simple algebraic groups\, and show an\nanalogue of Phyllis Cassidy’s result for partial differential fields.
URL:https://www.math.ens.psl.eu/evenement/groups-definable-in-partial-differential-fields-with-an-automorphism/
LOCATION:Sophie Germain salle 1016.
CATEGORIES:Théorie des Modèles et Groupes
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Europe/Paris:20220208T150000
DTEND;TZID=Europe/Paris:20220208T180000
DTSTAMP:20260418T161444
CREATED:20220129T155631Z
LAST-MODIFIED:20220129T160053Z
UID:15136-1644332400-1644343200@www.math.ens.psl.eu
SUMMARY:Un après-midi de sous-groupes aleatoires invariants ou stationaires
DESCRIPTION:ZOOM: https://us02web.zoom.us/j/81548053762\nID: 815 4805 3762\nMot de passe:\nG est un Graphe de Cayley du groupe libre à 107 générateurs. Quel est\nle degré de ce graphe? Tapez le numéro à trois chiffres comme un mot\nde passe. \n15.00 – 15.45    Tsachik Gelander (Weizmann Institute)\, « Stationary\nrandom discrete subgroups of semisimple Lie groups » \n16.00 – 16.45     Matthieu Joseph (ENS Lyon)\, « Allosteric actions of\nsurface groups » \n17.15 – 18.00     Yair Hartman (Ben Gurion University)\,\n« Intersectional Invariant Random Subgroups » \nVous pourrez trouver les résumés sur le site du séminaire: \nhttps://sites.google.com/site/annaerschler/grseminar
URL:https://www.math.ens.psl.eu/evenement/un-apres-midi-de-sous-groupes-aleatoires-invariants-ou-stationaires/
LOCATION:Zoom
CATEGORIES:Séminaire de théorie des groupes à l’ENS
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Europe/Paris:20220202T110000
DTEND;TZID=Europe/Paris:20220202T120000
DTSTAMP:20260418T161444
CREATED:20220214T103412Z
LAST-MODIFIED:20220214T103412Z
UID:15206-1643799600-1643803200@www.math.ens.psl.eu
SUMMARY:Julien Marché\, raconte-moi la topologie quantique et le nombre d'or !
DESCRIPTION:Si la topologie quantique est née des travaux de Jones\, Kauffman et Witten à la fin des années 1980\, on peut lui trouver des racines plus anciennes. En partant des polynômes chromatiques des graphes (Birkhoff 1912)\, revisités par Tutte dans les années 1960\, on va expliquer comment en tirer des représentations des groupes modulaires des surfaces toujours liées au nombre d’or. Parmi elles\, le groupe de l’icosaèdre et l’uniformisation de surfaces trouvées par Hirzebruch.
URL:https://www.math.ens.psl.eu/evenement/julien-marche-raconte-moi-la-topologie-quantique-et-le-nombre-dor/
LOCATION:En salle W au DMA\, ou sur Zoom
CATEGORIES:Séminaire Raconte-moi
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Europe/Paris:20220121T154000
DTEND;TZID=Europe/Paris:20220121T171000
DTSTAMP:20260418T161444
CREATED:20220106T215337Z
LAST-MODIFIED:20220106T215337Z
UID:15010-1642779600-1642785000@www.math.ens.psl.eu
SUMMARY:Decidability via the tilting correspondence
DESCRIPTION:We discuss new decidability and undecidability results for mixed characteristic henselian fields\, whose proof goes via reduction to positive characteristic. The reduction uses extensively the theory of perfectoid fields and also the earlier Krasner-Kazhdan-Deligne principle. Our main results will be:\n(1) A relative decidability theorem for perfectoid fields. Using this\, we obtain decidability of certain tame fields of mixed characteristic.\n(2) An undecidability result for the asymptotic theory of all finite extensions of ℚ_p (fixed p) with cross-section.\nWe will also discuss a tentative step towards understanding the underlying model theory of arithmetic phenomena in this area\, by presenting a model-theoretic way of seeing the Fontaine-Wintenberger theorem
URL:https://www.math.ens.psl.eu/evenement/decidability-via-the-tilting-correspondence/
LOCATION:En ligne
CATEGORIES:Séminaire Géométrie et théorie des modèles
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Europe/Paris:20220121T140000
DTEND;TZID=Europe/Paris:20220121T153000
DTSTAMP:20260418T161444
CREATED:20220106T214555Z
LAST-MODIFIED:20220106T215523Z
UID:15001-1642773600-1642779000@www.math.ens.psl.eu
SUMMARY:Hensel minimality and counting in valued fields
DESCRIPTION:Hensel minimality is a new axiomatic framework for doing tame geometry in non-Archimedean fields\, aimed to mimic o-minimality. It is designed to be broadly applicable while having strong consequences. We will give a general overview of the theory of Hensel minimality. Afterwards\, we discuss arithmetic applications to counting rational points on definable sets in valued fields.\nThis is partially joint work with R. Cluckers\, I. Halupczok and S. Rideau-Kikuchi\, and partially with V. Cantoral-Farfan and K. Huu Nguyen.
URL:https://www.math.ens.psl.eu/evenement/hensel-minimality-and-counting-in-valued-fields/
LOCATION:En ligne
CATEGORIES:Séminaire Géométrie et théorie des modèles
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Europe/Paris:20220119T110000
DTEND;TZID=Europe/Paris:20220119T120000
DTSTAMP:20260418T161444
CREATED:20220117T083010Z
LAST-MODIFIED:20220117T083010Z
UID:15061-1642590000-1642593600@www.math.ens.psl.eu
SUMMARY:François Charles\, raconte-moi la mesure gaussienne sur les réseaux euclidiens !
DESCRIPTION:Je discuterai certaines des nombreuses applications de la mesure gaussienne sur les réseaux euclidiens en mathématiques et en informatique. Dans un deuxième temps\, j’expliquerai comment les mesures gaussiennes apparaissent dans l’étude de certains réseaux de rang infini\, quelles sont les concepts mathématiques qui apparaissent dans cette situation\, et je donnerai des applications arithmétiques.
URL:https://www.math.ens.psl.eu/evenement/francois-charles-raconte-moi-la-mesure-gaussienne-sur-les-reseaux-euclidiens/
LOCATION:En salle W au DMA\, ou sur Zoom
CATEGORIES:Algèbre et géométrie,Séminaire Raconte-moi
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Europe/Paris:20220111T150000
DTEND;TZID=Europe/Paris:20220111T180000
DTSTAMP:20260418T161444
CREATED:20220109T083122Z
LAST-MODIFIED:20220109T091352Z
UID:15035-1641913200-1641924000@www.math.ens.psl.eu
SUMMARY:Après-midi de moyennabilité
DESCRIPTION:ZOOM: https://us02web.zoom.us/j/88011323267\nID: 880 1132 3267\nMot de passe:\nG est un Graphe de Cayley du groupe libre à 107 générateurs. Quel est le\ndegré de ce graphe? Tapez le numéro à trois chiffres comme un mot de\npasse. \n15.00 – 15.45     Friedrich Martin Schneider (Freiberg)\, « Concentration of\ninvariant means » \n16.00 – 16.45      Eduardo Scarparo (Federal University of Santa\nCatarina)\, « Amenability and unitary representations of groups of dynamical\norigin » \n17.15 – 18.00     Gidi Amir (Bar Ilan)\, « Amenability of quadratic activity\nautomata groups » \nhttps://sites.google.com/site/annaerschler/grseminar
URL:https://www.math.ens.psl.eu/evenement/apres-midi-de-moyennabilite/
LOCATION:Zoom
CATEGORIES:Séminaire de théorie des groupes à l’ENS
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Europe/Paris:20220105T110000
DTEND;TZID=Europe/Paris:20220105T120000
DTSTAMP:20260418T161444
CREATED:20211226T164951Z
LAST-MODIFIED:20220103T145206Z
UID:14937-1641380400-1641384000@www.math.ens.psl.eu
SUMMARY:Viviane Baladi : billards chaotiques et espaces anisotropes\, le mariage réussi de la carpe et du lapin !
DESCRIPTION:Les espaces de distributions anisotropes sont des outils efficaces pour étudier les propriétés statistiques de dynamiques chaotiques assez régulières\, en reliant ces propriétés au spectre d’un opérateur de type Perron-Frobenius agissant sur ces espaces. Les billards dispersifs (ou billards de Sinai) sont un exemple de dynamique chaotique naturel\, mais très peu régulier : la dynamique est seulement lisse par morceaux\, avec des dérivées non bornées et les « feuilletages dynamiques » sont seulement mesurables. J’expliquerai comment on a pu malgré tout définir et utiliser les espaces anisotropes avec succès dans ce contexte (notamment pour obtenir le mélange exponentiel de la mesure de Liouville du flot billard et construire la mesure maximisant l’entropie de l’application billard). (Travaux avec M. Demers et/ou C. Liverani. J’évoquerai\, si le temps le permet\, des travaux en cours de membres de mon groupe à Jussieu.)
URL:https://www.math.ens.psl.eu/evenement/viviane-baladi-billards-chaotiques-et-espaces-anisotropes-le-mariage-reussi-de-la-carpe-et-du-lapin/
LOCATION:En hybride\, 45 rue d'Ulm\, Paris\, 75005
CATEGORIES:Séminaire Raconte-moi
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Europe/Paris:20211202T090000
DTEND;TZID=Europe/Paris:20211202T120000
DTSTAMP:20260418T161444
CREATED:20211202T080000Z
LAST-MODIFIED:20211104T114114Z
UID:14115-1638435600-1638446400@www.math.ens.psl.eu
SUMMARY:On dp-finite fields
DESCRIPTION:Shelah’s conjecture predicts that any infinite NIP field iseither separably closed\, real closed or admits a non-trivial henselianvaluation. Recently\, Johnson proved that Shelah’s conjecture holds forfields of finite dp-rank\, also known as dp-finite fields. The aim of these two talks is to give an introduction to dp-rank in some algebraic structures and an overview of Johnson’s work.In the first talk\, we define dp-rank (which is a notion of rank in NIP theories) and give examples of dp-finite structures. In particular\, we discuss the dp-rank of ordered abelian groups and use them to construct multitude of examples of dp-finite fields. We also prove that every dp-finite field is perfect and sketch a proof that any valued field of dp-rank 1 is henselian.In the second talk\, we give an overview of Johnson’s proof that everyinfinite dp-finite field is either algebraically closed\, real closed oradmits a non-trivial henselian valuation. Crucially\, this relies on the notion of a W-topology\, a natural generalization of topologies arising from valuations\, and the construction of a definable W-topology on asufficiently saturated unstable dp-finite field.
URL:https://www.math.ens.psl.eu/evenement/on-dp-finite-fields-2/
LOCATION:Zoom
CATEGORIES:Séminaire Géométrie et théorie des modèles
END:VEVENT
END:VCALENDAR