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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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DTSTART:20220327T010000
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BEGIN:VEVENT
DTSTART;TZID=Europe/Paris:20230222T140000
DTEND;TZID=Europe/Paris:20230222T170000
DTSTAMP:20260418T161447
CREATED:20230215T213034Z
LAST-MODIFIED:20230215T213034Z
UID:16293-1677074400-1677085200@www.math.ens.psl.eu
SUMMARY:Un après-midi de théorie des groupes
DESCRIPTION:Le séminaire sera dans salle W et retransmis sur Zoom : \nhttps://https://us02web.zoom.us/j/81313173812\nMeeting ID: 813 1317 3812\nMot de passe:\nG est un Graphe de Cayley du groupe libre à 107 générateurs. Quel est le degré de ce graphe? Tapez le numéro à trois chiffres comme un mot de passe. \n14.00-14.45 Yves Benoist (Orsay)\, Harmonic functions on the Heisenberg\ngroup\n\n15.00-15.45 Nora  Szakacs (Manchester)\, Inverse semigroups as metric\nspaces\, and their uniform Roe algebras.\n\n16.00-16.45 Richard Aoun (Marne-la-Vallée)\,  Concentration\ninequalities for random walks on hyperbolic spaces\, and applications.
URL:https://www.math.ens.psl.eu/evenement/un-apres-midi-de-theorie-des-groupes-5/
LOCATION:ENS (salle W)
CATEGORIES:Séminaire de théorie des groupes à l’ENS
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Europe/Paris:20230110T140000
DTEND;TZID=Europe/Paris:20230110T170000
DTSTAMP:20260418T161447
CREATED:20230106T173826Z
LAST-MODIFIED:20230106T173826Z
UID:16229-1673359200-1673370000@www.math.ens.psl.eu
SUMMARY:Un après-midi de théorie des groupes
DESCRIPTION:Le séminaire sera dans salle W et retransmis sur Zoom : \nhttps://us02web.zoom.us/j/83858227469\nMeeting ID: 838 5822 7469 \nMot de passe:\nG est un Graphe de Cayley du groupe libre à 107 générateurs. Quel est le degré de ce graphe? Tapez le numéro à trois chiffres comme un mot de passe. \n14.00 – 14.45 Greg Kuperberg (UC Davis & IHES)\, An obstruction to quantum algorithms from small cancellation theory \n15.00 – 15.45 Konstantinos Tsouvalas (IHES )\, Linear hyperbolic groups indiscrete in rank 1 and products \n16.00 – 16.45 Delaram Kahrobaei (Cuny & IHES)\, Applied Group Theory in the Quantum and Artificial Intelligence Era
URL:https://www.math.ens.psl.eu/evenement/un-apres-midi-de-theorie-des-groupes-4/
LOCATION:ENS (salle W)
CATEGORIES:Algèbre et géométrie,Séminaire de théorie des groupes à l’ENS
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Europe/Paris:20221220T140000
DTEND;TZID=Europe/Paris:20221220T170000
DTSTAMP:20260418T161447
CREATED:20221216T214153Z
LAST-MODIFIED:20221216T214153Z
UID:16209-1671544800-1671555600@www.math.ens.psl.eu
SUMMARY:Un après-midi de théorie des groupes
DESCRIPTION:Le séminaire sera dans salle W et retransmis sur Zoom : \nhttps://us02web.zoom.us/j/89219979639\nMeeting ID: 892 1997 9639\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 Jim Belk (University of Glasgow)\,\n"Embeddings into Finitely Presented Simple Groups" (in presence\, room W)\n\n15.00 -- 15.45 Mark Pengitore (University of Virginia)\, "Characteristic\nquotients of surface groups and residual finiteness of mapping class\ngroups" (online\, shown on the screen)\n\n16.00 -- 16.45 Nikolay Bogachev (Weizmann Institute\, IITP RAS)\, "On geometry\nand arithmetic of hyperbolic orbifolds" (TBC\, online\, shown on the screen)
URL:https://www.math.ens.psl.eu/evenement/un-apres-midi-de-theorie-des-groupes-3/
LOCATION:14:00-17:00 Salle W
CATEGORIES:Séminaire de théorie des groupes à l’ENS
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Europe/Paris:20221209T160000
DTEND;TZID=Europe/Paris:20221209T173000
DTSTAMP:20260418T161447
CREATED:20221206T135217Z
LAST-MODIFIED:20221206T135217Z
UID:16179-1670601600-1670607000@www.math.ens.psl.eu
SUMMARY:Integer points on analytic sets
DESCRIPTION:In 2004 I proved that that if C is a transcendental curve definable in the structure R_{an}\, then the number of points on C with integer coordinates of modulus less than H\, is bounded by k loglog H for some constsnt k depending only on C. (The situation is vastly different for rational points.) The proof used the fact that such sets C are\, in fact\, semi-analytic everywhere-including infinity-and so the crux of the matter was to bound the number of solutions to equations of the form \n(*)    F(1/n) = 1/mfor n\, m integers bounded in modulus by (large) H\, and where F is a non-algebraic\, analytic function defined on an open interval containing 0.\nIt turns out that there is probably no generalization of the 2004 result for arbitrary R_{an}-definable sets (which need not be globally\, or even locally\, semi-analytic) but inspired by observations of Gareth Jones and Gal Binyamini\, the three of us began looking at equations of the form (*) in many variables and I shall be reporting on our results.
URL:https://www.math.ens.psl.eu/evenement/integer-points-on-analytic-sets/
LOCATION:Salle W (Toits du DMA)
CATEGORIES:Séminaire Géométrie et théorie des modèles
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Europe/Paris:20221209T141500
DTEND;TZID=Europe/Paris:20221209T154500
DTSTAMP:20260418T161447
CREATED:20221206T135049Z
LAST-MODIFIED:20221206T135049Z
UID:16177-1670595300-1670600700@www.math.ens.psl.eu
SUMMARY:Un théorème de finitude pour les fonctions tropicales sur les squelettes
DESCRIPTION:Les squelettes sont des sous-ensembles linéaires par morceaux d’espaces analytiques non-archimédiens apparaissant naturellement dans nombre de situations. Nous présenterons un résultat général de finitude\, obtenu en collaboration avec A. Ducros\, E. Hrushovski et J. Ye\, concernant le groupe abélien ordonné des fonctions tropicales sur les squelettes des analytifiés de Berkovich de variétés algébriques. Notre approche utilise la version modèle théorique de l’analytification (la complétion stable) développée dans un travail antérieur avec E. Hrushovski.
URL:https://www.math.ens.psl.eu/evenement/un-theoreme-de-finitude-pour-les-fonctions-tropicales-sur-les-squelettes/
LOCATION:Salle W (Toits du DMA)
CATEGORIES:Séminaire Géométrie et théorie des modèles
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Europe/Paris:20221125T160000
DTEND;TZID=Europe/Paris:20221125T173000
DTSTAMP:20260418T161447
CREATED:20221122T152916Z
LAST-MODIFIED:20221122T152916Z
UID:16127-1669392000-1669397400@www.math.ens.psl.eu
SUMMARY:On non-Diophantine sets in rings of functions
DESCRIPTION:For a ring R\, a subset of a cartesian power of R is said to be Diophantine if it is positive existentially definable over R with parameters from R. In general\, Diophantine sets over rings are not well-understood even in very natural situations; for instance\, we do not know if the ring of integers Z is Diophantine in the field of rational numbers. To show that a set is Diophantine requires to produce a particular existential formula that defines it. However\, to show that a set is not Diophantine is a more subtle task; in lack of a good description of Diophantine sets it requires to find at least a property shared by all of them. I will give an outline of some recent joint work with Garcia-Fritz and Pheidas on showing that several sets and relations over rings of polynomials and rational functions that are not Diophantine.
URL:https://www.math.ens.psl.eu/evenement/on-non-diophantine-sets-in-rings-of-functions/
LOCATION:IHP salle 01 et zoom
CATEGORIES:Séminaire Géométrie et théorie des modèles
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Europe/Paris:20221125T141500
DTEND;TZID=Europe/Paris:20221125T154500
DTSTAMP:20260418T161447
CREATED:20221122T152504Z
LAST-MODIFIED:20221122T152638Z
UID:16123-1669385700-1669391100@www.math.ens.psl.eu
SUMMARY:Abundance of strongly minimal autonomous differential equations
DESCRIPTION:In several classical families of differential equations such as the Painlevé families (Nagloo\, Pillay) or finite dimensional families of Schwarzian differential equations (Blazquez-Sanz\, Casale\, Freitag\, Nagloo)\, the following picture has been obtained regarding the transcendence properties of their solutions: \n– (Strong minimality): outside of an exceptional set of parameters\, the corresponding differential equations are strongly minimal\,\n– (Geometric triviality): algebraic independence of several solutions is controlled by pairwise algebraic independence outside of this exceptional set of parameters\,\n– (Multidimensionality): the differential equations defined by generic independent parameters are orthogonal. \nAre the families of differential equations satisfying such transcendence properties scarce or abundant in the universe of algebraic differential equations? \nI will describe an abundance result for families of autonomous differential equations satisfying the first two properties. The model-theoretic side of the proof uses a fine understanding of the structure of autonomous differential equations internal to the constants that we have recently obtained in a joint work with Rahim Moosa. The geometric side of the proof uses a series of papers of S.C. Coutinho and J.V. Pereira on the dynamical properties of a generic foliation.
URL:https://www.math.ens.psl.eu/evenement/abundance-of-strongly-minimal-autonomous-differential-equations/
LOCATION:IHP salle 01
CATEGORIES:Séminaire Géométrie et théorie des modèles
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Europe/Paris:20221125T110000
DTEND;TZID=Europe/Paris:20221125T123000
DTSTAMP:20260418T161447
CREATED:20221122T152309Z
LAST-MODIFIED:20221122T152714Z
UID:16121-1669374000-1669379400@www.math.ens.psl.eu
SUMMARY:Taming perfectoid fields
DESCRIPTION:Tilting perfectoid fields\, developed by Scholze\, allows to transfer results between certain henselian fields of mixed characteristic and their positive characteristic counterparts and vice versa. We present a model-theoretic approach to tilting via ultraproducts\, which allows to transfer many first-order properties between a perfectoid field and its tilt (and conversely). In particular\, our method yields a simple proof of the Fontaine-Wintenberger Theorem which states that the absolute Galois group of a perfectoid field and its tilt are canonically isomorphic. A key ingredient in our approach is an Ax-Kochen/Ershov principle for perfectoid fields (and generalizations thereof).\nThis is joint work with Konstantinos Kartas.
URL:https://www.math.ens.psl.eu/evenement/taming-perfectoid-fields/
LOCATION:IHP salle 01
CATEGORIES:Séminaire Géométrie et théorie des modèles
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Europe/Paris:20221122T140000
DTEND;TZID=Europe/Paris:20221122T170000
DTSTAMP:20260418T161447
CREATED:20221118T212841Z
LAST-MODIFIED:20221118T213000Z
UID:16113-1669125600-1669136400@www.math.ens.psl.eu
SUMMARY:Un après-midi de théorie des groupes
DESCRIPTION:Le séminaire sera dans salle W et retransmis sur Zoom : \nhttps://us02web.zoom.us/j/86001581637\nMeeting ID: 860 0158 1637\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 Anne Lonjou  (UPV/EHU\, University of the Basque Country)\,\n"Cremona goup over finite fields and Neretin groups"\n\n15.00 -- 15.45 Eduardo Silva (ENS\, Paris)\, "Dead ends on wreath products\nand lamplighter groups"\n\n16.00 -- 16.45 Alina Vdovina (CUNY\, New York)\, "Higher structures in\nmathematics: buildings\, k-graphs and C*-algebras"
URL:https://www.math.ens.psl.eu/evenement/16113/
LOCATION:14:00-17:00 Salle W
CATEGORIES:Séminaire de théorie des groupes à l’ENS
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Europe/Paris:20221019T140000
DTEND;TZID=Europe/Paris:20221019T170000
DTSTAMP:20260418T161447
CREATED:20221019T085810Z
LAST-MODIFIED:20221019T085810Z
UID:16061-1666188000-1666198800@www.math.ens.psl.eu
SUMMARY:Un après-midi de théorie des groupes
DESCRIPTION:Le séminaire sera dans salle W et retransmis sur Zoom : \nhttps://us02web.zoom.us/j/83927866358\nMeeting ID: 839 2786 6358 \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 Yury Neretin (University of Vienna)\, « Infinite symmetric\ngroups and cobordisms of triangulated surfaces » \n15.00 – 15.45 Matteo Tarocchi (University of Milano-Biocca)\,\n« Thompson-like groups acting on fractals » \n16.00 – 16.45 Rachel Skipper (ENS)\, « Maximal Subgroups of Thompson’s group V » \n 
URL:https://www.math.ens.psl.eu/evenement/un-apres-midi-de-theorie-des-groupes-2/
LOCATION:14:00-17:00 Salle W
CATEGORIES:Séminaire de théorie des groupes à l’ENS
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Europe/Paris:20220629T110000
DTEND;TZID=Europe/Paris:20220629T120000
DTSTAMP:20260418T161447
CREATED:20220620T113932Z
LAST-MODIFIED:20220627T193238Z
UID:15682-1656500400-1656504000@www.math.ens.psl.eu
SUMMARY:Anthony Várilly Alvarado\, raconte-moi comment utiliser la géométrie pour construire des codes pour le stockage à grande échelle !
DESCRIPTION:Motivated by large-scale storage problems around data loss\, a budding branch of coding theory has surfaced in the last decade or so\, centered around locally recoverable codes.  A code is a subset of a finite-dimensional vector space over a finite field\, chosen carefully so that all its elements are locally isolated\, as if they were « repelling » each other.  Each vector in a code is called a code word.  Locally recoverable codes have the property that individual entries in a code word are functions of other entries in the same word.  If an entry is accidentally lost\, it can be recomputed\, and hence a code word can be repaired.  Algebraic geometry has a role to play in the design of codes with locality properties. In this talk I will explain how to use algebraic surfaces to both reinterpret constructions of optimal codes already found in the literature\, and to find new locally recoverable codes\, many of which are optimal.
URL:https://www.math.ens.psl.eu/evenement/anthony-vrilly-alvarado-que-vas-tu-nous-raconter/
LOCATION:En salle W au DMA\, ou sur Zoom
CATEGORIES:Algèbre et géométrie,Séminaire Raconte-moi
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Europe/Paris:20220614T160000
DTEND;TZID=Europe/Paris:20220614T173000
DTSTAMP:20260418T161447
CREATED:20220607T105456Z
LAST-MODIFIED:20220607T105456Z
UID:15638-1655222400-1655227800@www.math.ens.psl.eu
SUMMARY:On the Borel complexity of modules
DESCRIPTION:We prove that among all countable\, commutative rings R (with unit) the theory of R-modules is not Borel complete if and only if there are only countably many non-isomorphic countable R-modules. From the proof\, we obtain a succinct proof that the class of torsion free abelian groups is Borel complete.\nThe results above follow from some general machinery that we expect to have applications in other algebraic settings. Here\, we also show that for an arbitrary countable ring R\, the class of left R-modules equipped with an endomorphism is Borel complete; as is the class of left R-modules equipped with predicates for four submodules. This is joint work with D. Ulrich.
URL:https://www.math.ens.psl.eu/evenement/on-the-borel-complexity-of-modules/
LOCATION:Sophie Germain salle 1016.
CATEGORIES:Théorie des Modèles et Groupes
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Europe/Paris:20220607T160000
DTEND;TZID=Europe/Paris:20220607T173000
DTSTAMP:20260418T161447
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:20260418T161447
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:20260418T161447
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:20260418T161447
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:20260418T161447
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:20260418T161447
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:20260418T161447
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:20260418T161447
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:20260418T161447
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:20260418T161447
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:20260418T161447
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:20260418T161447
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:20260418T161447
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:20260418T161447
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:20260418T161447
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:20260418T161447
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:20260418T161447
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:20260418T161447
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
END:VCALENDAR