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X-WR-CALNAME:Département de mathématiques et applications
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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:20170326T010000
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TZOFFSETFROM:+0200
TZOFFSETTO:+0100
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DTSTART:20171029T010000
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BEGIN:VEVENT
DTSTART;TZID=Europe/Paris:20170922T163000
DTEND;TZID=Europe/Paris:20170922T173000
DTSTAMP:20260423T012210
CREATED:20170922T143000Z
LAST-MODIFIED:20211104T104728Z
UID:8402-1506097800-1506101400@www.math.ens.psl.eu
SUMMARY:Algebraic structures and descent by symmetric monoidal categories and Deligne's Theory
DESCRIPTION:Let W be a finite dimensional algebraic structure over a field K of characteristic zero (for example an algebra or a graded algebra). In this talk I will explain how to construct a symmetric monoidal category CW which is (up to some categorical data) a complete invariant of W. This category will be a form of RepK-G\, where G is the algebraic group of automorphisms of W\, over some subfield K0 of K. The field K0 can be thought of as the field of invariants of W\, in a way which I will make precise.By using the theory of Deligne on symmetric monoidal categories I will show how one can use this category to construct a generic form of W\, and to study scalar invariants of W. Moreover\, I will show that forms of the structure W are in one to one correspondence with fiber functors from this category.I will give some examples of this category when W is a central simple algebra or a module over a given central simple algebra. I will also explain how one can use this category to study embeddings of projective varieties in projective spaces and study questions about field of definition.
URL:https://www.math.ens.psl.eu/evenement/algebraic-structures-and-descent-by-symmetric-monoidal-categories-and-delignes-theory/
LOCATION:ENS Salle W
CATEGORIES:Variétés rationnelles
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Europe/Paris:20170922T150000
DTEND;TZID=Europe/Paris:20170922T160000
DTSTAMP:20260423T012210
CREATED:20170922T130000Z
LAST-MODIFIED:20211104T104529Z
UID:8401-1506092400-1506096000@www.math.ens.psl.eu
SUMMARY:Cayley groups
DESCRIPTION:I will start the talk with the classical Cayley transform for the special orthogonal group SO(n) defined by Arthur Cayley in 1846. A connected linear algebraic group G over a field K is called a Cayley group if it admits a Cayley map\, that is\, a G-equivariant birational isomorphism between the group variety G and its Lie algebra Lie(G). For example\, SO(n) is a Cayley group. A linear algebraic group G is called stably Cayley if G x (K*)^r is Cayley for some natural number r. I will consider semisimple algebraic groups\, in particular\, simple algebraic groups. I will describe classification of Cayley simple groups and of stably Cayley semisimple groups over an algebraically closed field of characteristic 0 (Based on joint works with Boris Kunyavskii and others).
URL:https://www.math.ens.psl.eu/evenement/cayley-groups/
LOCATION:ENS Salle W
CATEGORIES:Variétés rationnelles
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Europe/Paris:20170609T163000
DTEND;TZID=Europe/Paris:20170609T173000
DTSTAMP:20260423T012210
CREATED:20170609T143000Z
LAST-MODIFIED:20211104T104312Z
UID:8391-1497025800-1497029400@www.math.ens.psl.eu
SUMMARY:La conjecture de Manin pour une famille d'hypersurfaces projectives.
DESCRIPTION:Les conjectures de Manin et Peyre décrivent la répartition des points rationnels de hauteur bornée sur une variété de Fano en terme d’invariants géométriques de cette variété. S’inspirant de travaux récents de La Bretèche et de Blomer\, Brüdern et Salberger\, on s’intéressera au cours de cet exposé aux conjectures de Manin et de Peyre dans le cas des hypersurfaces singulières de P^{2n-1} définies sur Q par les équations suivantes : x_1 y_2 ?R y_n + x_2 y_2 y_3 ?R y_n + ?R + x_n y_1 y_2 ?R y_{n-1} = 0\, pour tout n ?oo 3.
URL:https://www.math.ens.psl.eu/evenement/la-conjecture-de-manin-pour-une-famille-dhypersurfaces-projectives/
LOCATION:ENS Salle W
CATEGORIES:Variétés rationnelles
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Europe/Paris:20170609T150000
DTEND;TZID=Europe/Paris:20170609T160000
DTSTAMP:20260423T012210
CREATED:20170609T130000Z
LAST-MODIFIED:20211104T104312Z
UID:8390-1497020400-1497024000@www.math.ens.psl.eu
SUMMARY:Many cubic surfaces contain rational points.
DESCRIPTION:I will discuss the arithmetic of cubic surfaces and show how recent work on Mordell curves allows one to say something unconditional about the existence of rational points on a family of cubic surfaces.
URL:https://www.math.ens.psl.eu/evenement/many-cubic-surfaces-contain-rational-points/
LOCATION:ENS Salle W
CATEGORIES:Variétés rationnelles
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Europe/Paris:20170523T140000
DTEND;TZID=Europe/Paris:20170523T170000
DTSTAMP:20260423T012210
CREATED:20170523T120000Z
LAST-MODIFIED:20211104T104311Z
UID:8389-1495548000-1495558800@www.math.ens.psl.eu
SUMMARY:Trois exposés dans un après-midi de théorie des groupes
DESCRIPTION:
URL:https://www.math.ens.psl.eu/evenement/trois-exposes-dans-un-apres-midi-de-theorie-des-groupes/
LOCATION:Salle W DMA ENS
CATEGORIES:Séminaire de théorie des groupes à l’ENS
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Europe/Paris:20170519T160000
DTEND;TZID=Europe/Paris:20170519T160000
DTSTAMP:20260423T012210
CREATED:20170519T140000Z
LAST-MODIFIED:20211104T104256Z
UID:8385-1495209600-1495209600@www.math.ens.psl.eu
SUMMARY:Zéros et points rationnels des fonctions analytiques ou oscillant.
DESCRIPTION:Compter les points rationnels de hauteur bornée dans le graphe d’une fonction\, ou plus généralement d’une courbe (plane)\, se ramène à estimer le nombre Z_d de points d’intersection de cette courbe avec un ensemble algébrique de degré d donné. J’expliquerai     – d’une part comment on peut produire des familles de fonctions analytiques sur [0\,1] telle que Z_d est polynomialement borné en d\, et comment une telle borne assure que le graphe d’une telle fonction recèle moins de log?(T) points rationnels de hauteur < T\,      – d'autre part comment on peut traiter le cas de certaines courbes oscillant (ie non o-minimales) pour obtenir encore une borne du type log?(T). Il s'agit de travaux en commun avec Y. Yomdin d'une part et C. Miller d'autre part.
URL:https://www.math.ens.psl.eu/evenement/zeros-et-points-rationnels-des-fonctions-analytiques-ou-oscillant/
LOCATION:Salle W
CATEGORIES:Séminaire Géométrie et théorie des modèles
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Europe/Paris:20170519T141500
DTEND;TZID=Europe/Paris:20170519T141500
DTSTAMP:20260423T012210
CREATED:20170519T121500Z
LAST-MODIFIED:20211104T104256Z
UID:8384-1495203300-1495203300@www.math.ens.psl.eu
SUMMARY:Tame Expansions of o-minimal Structures
DESCRIPTION:Expanding a model theoretically `tame’ structure in a way that it stays `tame’ has been a theme in the recent years. In the first part of this talk\, we present a history of work done in that frame. Then we focus on the case of expansions of o-minimal structures by a unary predicate. There is a dividing line according to whether the predicate is dense or discrete
URL:https://www.math.ens.psl.eu/evenement/tame-expansions-of-o-minimal-structures/
LOCATION:Salle W ENS
CATEGORIES:Séminaire Géométrie et théorie des modèles
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Europe/Paris:20170519T110000
DTEND;TZID=Europe/Paris:20170519T110000
DTSTAMP:20260423T012210
CREATED:20170519T090000Z
LAST-MODIFIED:20211104T104256Z
UID:8383-1495191600-1495191600@www.math.ens.psl.eu
SUMMARY:Beyond o-minimality\, and why
DESCRIPTION:O-minimal structures on the real field have many desirable properties. As examples:     (a) Hausdorff (and even packing) dimension agrees with topological dimension on locally closed definable sets.    (b) Locally closed definable sets have few rational points (in the sense of the Pila-Wilkie Theorem).    (c) For each positive integer p\, every closed definable set is the zero set of a definable C^p function.    (d) Connected components of definable sets are definable.But to what extent is o-minimality necessary for these properties to hold? I will discuss this question\, and illustrate via examples as to why one might care about answers.
URL:https://www.math.ens.psl.eu/evenement/beyond-o-minimality-and-why/
LOCATION:Salle W ENS
CATEGORIES:Séminaire Géométrie et théorie des modèles
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Europe/Paris:20170516T160000
DTEND;TZID=Europe/Paris:20170516T173000
DTSTAMP:20260423T012210
CREATED:20170516T140000Z
LAST-MODIFIED:20211104T104257Z
UID:8386-1494950400-1494955800@www.math.ens.psl.eu
SUMMARY:Courbes auto-évitantes et isomorphisme local
DESCRIPTION:La notion d’isomorphisme local a été introduite pour l’étude des pavages apériodiques (pavages de penrose\, quasicristaux…). On considère un espace euclidien de dimension finie. On identifie deux sous-ensembles si et seulement s’ils sont équivalents à translation près. On dit qu’un sous-ensemble E satisfait la propriété d’isomorphisme local si chaque partie bornée de E apparaît dans toute boule de rayon suffisamment grand. Deux sous-ensembles E\,F sont localement isomorphes si toute partie bornée de l’un apparaît aussi dans l’autre.Deux pavages sont élémentairement équivalents si et seulement s’ils sont localement isomorphes. Les pavages de Penrose d’un même type sont localement isomorphes entre eux et satisfont la propriété d’isomorphisme local.Ici\, nous considérons trois familles de courbes auto-évitantes introduites par B. Mandelbrot pour construire des fractales. Nous montrons que chacune donne des recouvrements du plan\, constitués chacun par une courbe auto-évitante ou par un petit nombre de telles courbes disjointes\, qui satisfont la propriété d’isomorphisme local. Nous caractérisons la relation d’isomorphisme local entre les recouvrements d’une même famille.
URL:https://www.math.ens.psl.eu/evenement/courbes-auto-evitantes-et-isomorphisme-local/
LOCATION:Sophie Germain salle 1016
CATEGORIES:Théorie des Modèles et Groupes
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Europe/Paris:20170512T163000
DTEND;TZID=Europe/Paris:20170512T173000
DTSTAMP:20260423T012210
CREATED:20170512T143000Z
LAST-MODIFIED:20211104T104311Z
UID:8388-1494606600-1494610200@www.math.ens.psl.eu
SUMMARY:On the classification of quadratic forms over an integral domain of a global function field.
DESCRIPTION:Let C be a smooth projective curve defined over the finite field F_q (q is odd) and let K=F_q(C) be its function field. Any (non-empty) finite set S of closed points of C gives rise to an integral domain O_S := F_q[C-S] in K. We show that given an O_S-regular quadratic space (V\,q) of rank n ?oo 3\, the set of genera in the proper classification of quadratic O_S-spaces isomorphic to (V\,q) in the flat or étale topology\, is in 1:1 correspondence with 2.Br(O_S)\, thus there are 2|S|-1 genera. Furthermore\, if (V\,q) is isotropic\, then the abelian group Pic(O_S)/2 classifies the forms in the genus Cl_S(O_q) of (V\,q). For n ?oo 5\, this is true for all genera\, hence the full classification is via the abelian group H2_ét(O_S\,?_2). If time permits\, we shall see when V is split by a hyperbolic plane H(L_0)\, an explicit isomorphism Pic(O_S)/2 –> Cl_S(O_q)\, and in case C is an elliptic curve and S={?} where ? is F_q-rational\, an algorithm producing representatives of classes in Cl_S(O_q).
URL:https://www.math.ens.psl.eu/evenement/on-the-classification-of-quadratic-forms-over-an-integral-domain-of-a-global-function-field/
LOCATION:ENS Salle W
CATEGORIES:Variétés rationnelles
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Europe/Paris:20170512T150000
DTEND;TZID=Europe/Paris:20170512T160000
DTSTAMP:20260423T012210
CREATED:20170512T130000Z
LAST-MODIFIED:20211104T104310Z
UID:8387-1494601200-1494604800@www.math.ens.psl.eu
SUMMARY:Théorèmes de relèvement et cohomologie des groupes profinis lisses.
DESCRIPTION:La notion de groupe profini lisse permet d’axiomatiser les propriétés cohomologiques qui se déduisent du théorème de Hilbert 90 en cohomologie Galoisienne. L’objectif de cette introduction est de proposer une nouvelle approche effective à la conjecture de Bloch-Kato\, démontrée par Rost\, Suslin et Voevodsky. Un ingrédient clé est l’étude des puissances divisées de modules sur les vecteurs de Witt\, munies des opérateurs Frobenius et Verschiebung. On présentera quelques résultats partiels et applications d’intérêt propres\, notamment au relèvement des représentations Galoisiennes. Il s’agit d’un travail en cours avec Mathieu Florence.
URL:https://www.math.ens.psl.eu/evenement/theoremes-de-relevement-et-cohomologie-des-groupes-profinis-lisses/
LOCATION:ENS Salle W
CATEGORIES:Variétés rationnelles
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Europe/Paris:20170428T160000
DTEND;TZID=Europe/Paris:20170428T160000
DTSTAMP:20260423T012210
CREATED:20170428T140000Z
LAST-MODIFIED:20211104T104241Z
UID:8380-1493395200-1493395200@www.math.ens.psl.eu
SUMMARY:Séries linéaires limites et applications
DESCRIPTION:Je présente un formalisme combinatoire pour l’étude des dégénérescences des séries linéaires dans une famille de courbes algébriques. J’en déduis quelques applications dont notamment l’équirépartition selon la mesure admissible de Zhang des points de ramification des fibrés en droite sur les courbes de Berkovich\, un analogue non-archimédien du théorème de Mumford-Neeman. Je discuterai aussi la question de la convergence de la mesure d’Arakelov vers la mesure de Zhang dans une famille de surfaces de Riemann.
URL:https://www.math.ens.psl.eu/evenement/series-lineaires-limites-et-applications/
LOCATION:ENS Salle W
CATEGORIES:Séminaire Géométrie et théorie des modèles
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Europe/Paris:20170428T141500
DTEND;TZID=Europe/Paris:20170428T141500
DTSTAMP:20260423T012210
CREATED:20170428T121500Z
LAST-MODIFIED:20211104T104241Z
UID:8379-1493388900-1493388900@www.math.ens.psl.eu
SUMMARY:Triangulation des ensembles semi-algébriques p-adiques
DESCRIPTION:On sait que les ensembles semi-algébriques p-adiques admettent une décomposition cellulaire semblable à celle des semi-algébriques réels (Denef 1984). On sait aussi les classifier à bijection semi-algébrique près (Cluckers 2001)\, mais pas à homéomorphismes semi-algébriques près. En introduisant une notion appropriée de simplexe sur les corps p-adiquement clos\, on peut montrer que tout ensemble semi-algébrique p-adique est semi-algébriquement homéomorphe à un complexe simplicial p-adique\, exactement comme dans le cas réel clos. C’est ce résultat récent de `triangulation p-adique’ que je tâcherai de présenter\, avec ses applications les plus directes (existence de découpages avec contraintes aux bords\, existence de rétractions\, etc).
URL:https://www.math.ens.psl.eu/evenement/triangulation-des-ensembles-semi-algebriques-p-adiques/
LOCATION:ENS Salle W
CATEGORIES:Séminaire Géométrie et théorie des modèles
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Europe/Paris:20170428T110000
DTEND;TZID=Europe/Paris:20170428T110000
DTSTAMP:20260423T012210
CREATED:20170428T090000Z
LAST-MODIFIED:20211104T104241Z
UID:8378-1493377200-1493377200@www.math.ens.psl.eu
SUMMARY:Un théorème d'Ax-Lindemann non-archimédien
DESCRIPTION:On présentera un résultat de type Ax-Lindemann pour les produits de courbes de Mumford sur un corps p-adique. Notre preuve reprend en l’adaptant les grandes lignes de l’approche de Pila dans le cas archimédien. En particulier nous utilisons un théorème de Pila-Wilkie p-adique obtenu avec R. Cluckers et G. Comte. Il s’agit d’un travail en commun avec A. Chambert-Loir.
URL:https://www.math.ens.psl.eu/evenement/un-theoreme-dax-lindemann-non-archimedien/
LOCATION:ENS Salle W
CATEGORIES:Séminaire Géométrie et théorie des modèles
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Europe/Paris:20170421T163000
DTEND;TZID=Europe/Paris:20170421T173000
DTSTAMP:20260423T012210
CREATED:20170421T143000Z
LAST-MODIFIED:20211104T104255Z
UID:8382-1492792200-1492795800@www.math.ens.psl.eu
SUMMARY:Groupe de Brauer invariant et obstruction de descente itérée
DESCRIPTION:Pour une variété quasi-projective\, lisse\, géométriquement intègre sur un corps de nombre k\, on montre que l’obstruction de descente itérée est équivalente à l’obstruction de descente. Ceci répond une question ouverte de Poonen. L’idée clé est la notion de sous-groupe de Brauer invariant et la notion d’obstruction de Brauer-Manin invariant étale pour une k-variété munie d’une action d’un groupe linéaire connexe.
URL:https://www.math.ens.psl.eu/evenement/groupe-de-brauer-invariant-et-obstruction-de-descente-iteree/
LOCATION:ENS Salle W
CATEGORIES:Variétés rationnelles
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Europe/Paris:20170421T150000
DTEND;TZID=Europe/Paris:20170421T160000
DTSTAMP:20260423T012210
CREATED:20170421T130000Z
LAST-MODIFIED:20211104T104242Z
UID:8381-1492786800-1492790400@www.math.ens.psl.eu
SUMMARY:Fields of definition and essential dimension in representation theory
DESCRIPTION:A classical theorem of Brauer asserts that every finite-dimensional non-modular representation p of a finite group G defined over a field K\, whose character takes values in a subfield k\, descends to k\, provided that k has suitable roots of unity. If k does not contain these roots of unity\, it is natural to ask how far p is from being definable over k. The classical answer is given by the Schur index of p\, which is the smallest degree of a finite field extension l/k such that p can be defined over l. In this talk\, based on joint work with Nikita Karpenko\, Julia Pevtsova and Dave Benson\, I will discuss another invariant\, the essential dimension of p\, which measures how far p is from being definable over k in a different way\, by using transcendental\, rather than algebraic field extensions. This invariant is of interest in both the modular and the non-modular settings. I will also consider the question of which representations of finite groups or finite-dimensional associative algebras have a minimal field of definition with respect to inclusion.
URL:https://www.math.ens.psl.eu/evenement/fields-of-definition-and-essential-dimension-in-representation-theory/
LOCATION:ENS Salle W
CATEGORIES:Variétés rationnelles
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Europe/Paris:20170418T160000
DTEND;TZID=Europe/Paris:20170418T173000
DTSTAMP:20260423T012210
CREATED:20170418T140000Z
LAST-MODIFIED:20211104T104205Z
UID:8376-1492531200-1492536600@www.math.ens.psl.eu
SUMMARY:Actions localement quadratiques de groupes de Chevalley\, et représentations minuscules
DESCRIPTION:Un très beau théorème de Timmesfeld caractérise\, sans hypothèse sur K\, la représentation naturelle de G = SL(2\,K) parmi les Z[G]-modules : c’est le seul Z[G]-module irréductible V où les sous-groupes unipotents de G agissent `quadratiquement’\, i.e. [U\, U\, V] = 0 (en itérant les commutateurs).Montrer ce théorème\, c’est essentiellement savoir reconstruire sur un Z[G]-module quadratique une structure de K-espace vectoriel compatible avec l’action de G.L’exposé présentera une généralisation de ce théorème aux autres groupes de Chevalley simples : si G est un tel groupe\, et V un Z[G]-module sur lequel chaque sous-groupe racine (aussi appelé sous-groupe à un paramètre) agit quadratiquement dans le sens précédent\, alors V est en effet un K-espace vectoriel construit à partir de représentations dites `minuscules’ (concept qui sera expliqué).Enfin il y aura une petite application symbolique aux représentations de rang de Morley fini des groupes algébriques.
URL:https://www.math.ens.psl.eu/evenement/actions-localement-quadratiques-de-groupes-de-chevalley-et-representations-minuscules/
LOCATION:Sophie Germain salle 1016
CATEGORIES:Théorie des Modèles et Groupes
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Europe/Paris:20170404T140000
DTEND;TZID=Europe/Paris:20170404T170000
DTSTAMP:20260423T012210
CREATED:20170404T120000Z
LAST-MODIFIED:20211104T104240Z
UID:8377-1491314400-1491325200@www.math.ens.psl.eu
SUMMARY:trois exposés en théorie des groupes
DESCRIPTION:https://sites.google.com/site/annaerschler/programtalks
URL:https://www.math.ens.psl.eu/evenement/trois-exposes-en-theorie-des-groupes-2/
LOCATION:Salle W DMA ENS
CATEGORIES:Séminaire de théorie des groupes à l’ENS
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Europe/Paris:20170331T163000
DTEND;TZID=Europe/Paris:20170331T173000
DTSTAMP:20260423T012210
CREATED:20170331T143000Z
LAST-MODIFIED:20211104T104003Z
UID:8371-1490977800-1490981400@www.math.ens.psl.eu
SUMMARY:Finite descent obstruction and non-abelian reciprocity.
DESCRIPTION:For a nice algebraic variety X over a number field F\, one of the central problems of Diophantine Geometry is to locate precisely the set X(F) inside X(A)\, where A denotes the ring of adèles of F. One approach to this problem is provided by the finite descent obstruction\, which is defined to be the set of adelic points which can be lifted to twists of torsors for finite étale group schemes over F on X. More recently\, Kim proposed an iterative construction of another subset of X(A) which contains the set of rational points. In this talk\, we compare the two constructions. Our main result shows that the two approaches are equivalent.
URL:https://www.math.ens.psl.eu/evenement/finite-descent-obstruction-and-non-abelian-reciprocity/
LOCATION:ENS Salle W
CATEGORIES:Variétés rationnelles
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Europe/Paris:20170331T150000
DTEND;TZID=Europe/Paris:20170331T160000
DTSTAMP:20260423T012210
CREATED:20170331T130000Z
LAST-MODIFIED:20211104T104003Z
UID:8370-1490972400-1490976000@www.math.ens.psl.eu
SUMMARY:Wild ramification and K(pi\,1) spaces
DESCRIPTION:I will sketch the proof that every connected affine scheme in positivecharacteristic is a K(pi\,1) space for the etale topology.  The keytechnical ingredient is a ?RoeBertini-type?R statement regarding the wildramification of l-adic local systems on affine spaces. Its proof usesin an essential way recent advances in higher ramification theory dueto T. Saito.
URL:https://www.math.ens.psl.eu/evenement/wild-ramification-and-kpi1-spaces/
LOCATION:ENS Salle W
CATEGORIES:Variétés rationnelles
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Europe/Paris:20170328T160000
DTEND;TZID=Europe/Paris:20170328T160000
DTSTAMP:20260423T012210
CREATED:20170328T140000Z
LAST-MODIFIED:20211104T103601Z
UID:8360-1490716800-1490716800@www.math.ens.psl.eu
SUMMARY:NSOP_1\, Kim-independence\, and simplicity at a generic scale
DESCRIPTION:The class of NSOP_1 theories properly contains the simple theories and is contained in the class of theories without the tree property of the first kind. We will describe a notion of independence called Kim-independence\, which corresponds to non-forking independence ‘at a generic scale.’ In an NSOP_1 theory\, Kim-independence is symmetric and satisfies a version of Kim’s lemma and the independence theorem. Moreover\, these properties of Kim-independence individually characterize NSOP_1 theories. We will talk about what Kim-independence looks like in several concrete examples: parametrized equivalence relations\, Frobenius fields\, and vector spaces with a bilinear form. This is joint work with Itay Kaplan.
URL:https://www.math.ens.psl.eu/evenement/nsop_1-kim-independence-and-simplicity-at-a-generic-scale/
LOCATION:Sophie Germain salle 1016
CATEGORIES:Théorie des Modèles et Groupes
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Europe/Paris:20170321T140000
DTEND;TZID=Europe/Paris:20170321T170000
DTSTAMP:20260423T012210
CREATED:20170321T130000Z
LAST-MODIFIED:20211104T104202Z
UID:8372-1490104800-1490115600@www.math.ens.psl.eu
SUMMARY:Trois exposés en théorie des groupes
DESCRIPTION:14.00-14.45 Camille Horbez (Orsay): Boundary amenability of Out(Fn)15.00-15.45 Romain Tessera (Orsay): Poincaré profile in Hyperbolic groups15.45-16.15 pause café16.15-17.00 Yash Lodha (EPFL Lausanne): Nonamenable groups of piecewise projective homeomorphisms
URL:https://www.math.ens.psl.eu/evenement/trois-exposes-en-theorie-des-groupes/
LOCATION:ENS Toits du DMA salle W
CATEGORIES:Séminaire de théorie des groupes à l’ENS
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Europe/Paris:20170314T000000
DTEND;TZID=Europe/Paris:20170314T000000
DTSTAMP:20260423T012210
CREATED:20170313T230000Z
LAST-MODIFIED:20211104T104002Z
UID:8369-1489449600-1489449600@www.math.ens.psl.eu
SUMMARY:Kappa-bounded exponential groups and exponential-logarithmic power series fields without log-atomic elements
DESCRIPTION:A divisible ordered abelian group is an exponential group if its rank as an ordered set is isomorphic to its negative cone. Exponential groups appear as the value groups of ordered exponential fields\, and were studied in [1]. In [2] we gave an explicit construction of exponential groups as Hahn groups of series with support bounded in cardinality by an uncountable regular cardinal kappa. An exp-log series s is said to be log atomic if the nth-iterate of log(s) is a monomial for all n in N. In this talk I will present a modified construction of kappa-bounded Hahn groups and exploit it to construct kappa bounded Hahn fields without log-atomic elements. This is ongoing joint work with Berarducci\, Mantova and Matusinski.[1] S. Kuhlmann\, Ordered exponential fields\, The Fields Institute Monograph Series\, vol 12. Amer. Math. Soc. (2000) [2] S. Kuhlmann and S. Shelah\, Kappa-bounded Exponential-Logarithmic power series fields\, Annals Pure and Applied Logic\, 136\, 284-296 (2005)
URL:https://www.math.ens.psl.eu/evenement/kappa-bounded-exponential-groups-and-exponential-logarithmic-power-series-fields-without-log-atomic-elements/
LOCATION:Sophie Germain salle 1016
CATEGORIES:Théorie des Modèles et Groupes
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Europe/Paris:20170310T160000
DTEND;TZID=Europe/Paris:20170310T160000
DTSTAMP:20260423T012210
CREATED:20170310T150000Z
LAST-MODIFIED:20211104T104002Z
UID:8368-1489161600-1489161600@www.math.ens.psl.eu
SUMMARY:Satellites of spherical subgroups and Poincaré polynomials
DESCRIPTION:Let G be a connected reductive group over C. One can associate with every spherical homogeneous space G/H its lattice of weights X^*(G/H) and a subset S of M of linearly independent primitive lattice vectors which are called the spherical roots. For any subset I of S we define\, up to conjugation\, a spherical subgroup H_I in G such that dim H_I = dim H and X^*(G/H_I) = X^*(G/H). We call the subgroups H_I the satellites of the spherical subgroup H. Our interest in satellites H_I is motivated by the space of arcs of the spherical homogeneous space G/H.We show a close relation between the Poincaré polynomials of the two spherical homogeneous spaces G/H and G/H_I.All of this is useful for the computation of the stringy E-function of Q-Gorenstein spherical embeddings.The talk is based on joint works with Victor Batyrev.
URL:https://www.math.ens.psl.eu/evenement/satellites-of-spherical-subgroups-and-poincare-polynomials/
LOCATION:ENS Salle W
CATEGORIES:Séminaire Géométrie et théorie des modèles
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Europe/Paris:20170310T141500
DTEND;TZID=Europe/Paris:20170310T141500
DTSTAMP:20260423T012210
CREATED:20170310T131500Z
LAST-MODIFIED:20211104T104001Z
UID:8367-1489155300-1489155300@www.math.ens.psl.eu
SUMMARY:Quasianalytic Ilyashenko algebras
DESCRIPTION:In 1923\, Dulac published a proof of the claim that every real analytic vector field on the plane has only finitely many limit cycles (now known as Dulac’s Problem). In the mid-1990s\, Ilyashenko completed Dulac’s proof
URL:https://www.math.ens.psl.eu/evenement/quasianalytic-ilyashenko-algebras/
LOCATION:ENS Salle W
CATEGORIES:Séminaire Géométrie et théorie des modèles
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Europe/Paris:20170310T110000
DTEND;TZID=Europe/Paris:20170310T110000
DTSTAMP:20260423T012210
CREATED:20170310T100000Z
LAST-MODIFIED:20211104T103601Z
UID:8361-1489143600-1489143600@www.math.ens.psl.eu
SUMMARY:Rational points on families of curves
DESCRIPTION:The TAC (torsion anomalous conjecture) states that for an irreducible variety V embedded transversaly in an abelian variety A there are only finitely many maximal V-torsion anomalous varieties. It is well know that the TAC implies the Mordell-Lang conjecture. S. Checcole\, F. Veneziano and myself were trying to prove some new cases of the TAC. In this process we realised that some methods could be made not only effective but even explicit. So we analysed the implication of this explicit methods on the Mordell Conjeture. Namely: can we make the Mordell Conjecture explicit for some new families of curves and so determine all the rational points on these curves? Of course we started with the easiest situation\, that is curves in ExE for E an elliptic curve. We eventually could give some new families of curves of growing genus for which we can determine all the rational points. I will explain the difficulties and the ingredients of this result. I will then discuss the generalisations of the method and also its limits.
URL:https://www.math.ens.psl.eu/evenement/rational-points-on-families-of-curves/
LOCATION:ENS Salle W
CATEGORIES:Séminaire Géométrie et théorie des modèles
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Europe/Paris:20170307T160000
DTEND;TZID=Europe/Paris:20170307T160000
DTSTAMP:20260423T012210
CREATED:20170307T150000Z
LAST-MODIFIED:20211104T103801Z
UID:8364-1488902400-1488902400@www.math.ens.psl.eu
SUMMARY:Elimination of imaginaries for differentially closed fields of finite characteristic
DESCRIPTION:All fields under discussion here are assumed to have finite characteristic p. This talk might be seen as a sequel to my survey talk at Françoise Delon’s conference in June 2016\, although it will not assume familiarity with this talk.Of interest here are two complete theories\, namely differentially closed fields (DCF) and separably closed fields (inf-SCF) with infinite degree of imperfection. These theories are related. For example\, the underlying field of a model of DCF is a model of inf-SCF\, and the constant field is also a model of inf-SCF. In each case\, there are natural choices of language in which the theory has quantifier elimination.We will consider ways in which the theories are not alike. In the mid 1980’s Gabriel Srour proved that DCF is equational\, and also that the theories of separably closed fields of finite degree of imperfection are equational. However\, to my knowledge\, the equationality of inf-SCF is still unknown.Delon proved that the finite imperfection separably closed fields have elimination of imaginaries (EI)
URL:https://www.math.ens.psl.eu/evenement/elimination-of-imaginaries-for-differentially-closed-fields-of-finite-characteristic/
LOCATION:Sophie Germain salle 1016
CATEGORIES:Théorie des Modèles et Groupes
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Europe/Paris:20170228T160000
DTEND;TZID=Europe/Paris:20170228T160000
DTSTAMP:20260423T012210
CREATED:20170228T150000Z
LAST-MODIFIED:20211104T141026Z
UID:8359-1488297600-1488297600@www.math.ens.psl.eu
SUMMARY:Expansions minimales de (Z\,+\,0)
DESCRIPTION:Cet exposé essayera de donner une vision d’ensemble des différentes choses connu à ce jour sur les expansions du groupes des entiers (Z\,+\,0) avec un accent sur les expansions dp-minimales. En particulier les deux structures (Z\,+\,0\,
URL:https://www.math.ens.psl.eu/evenement/expansions-minimales-de-z0/
LOCATION:Sophie Germain salle 1016
CATEGORIES:Théorie des Modèles et Groupes
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Europe/Paris:20170224T163000
DTEND;TZID=Europe/Paris:20170224T173000
DTSTAMP:20260423T012210
CREATED:20170224T153000Z
LAST-MODIFIED:20211104T103802Z
UID:8366-1487953800-1487957400@www.math.ens.psl.eu
SUMMARY:Actions de p-groupes sur les variétés projectives.
DESCRIPTION:Je discuterai des contraintes que la géométrie d’une variété projective fait peser sur les possibles actions de p-groupes sur cette dernière. J’expliquerai en particulier comment le calcul d’invariants numériques\, tels que les nombres caractéristiques\, peut permettre de prévoir l’existence de points fixes.
URL:https://www.math.ens.psl.eu/evenement/actions-de-p-groupes-sur-les-varietes-projectives/
LOCATION:ENS Salle W
CATEGORIES:Variétés rationnelles
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Europe/Paris:20170224T150000
DTEND;TZID=Europe/Paris:20170224T160000
DTSTAMP:20260423T012210
CREATED:20170224T140000Z
LAST-MODIFIED:20211104T103801Z
UID:8365-1487948400-1487952000@www.math.ens.psl.eu
SUMMARY:Brauer groups and the Brauer-Manin sets of Kummer varieties.
DESCRIPTION:This is a joint work with Yuri Zarhin. We study Kummer varieties attached to 2-coverings of abelian varieties of arbitrary dimension. Over a number field we show that the subgroup of odd order elements of the Brauer group does not obstruct the Hasse principle. Sufficient conditions for the triviality of the Brauer group can be given\, which allow us to give an example of a Kummer K3 surface of geometric Picard rank 17 over the rationals with trivial Brauer group. We establish the non-emptyness of the Brauer-Manin set of everywhere locally soluble Kummer varieties attached to 2-coverings of products of hyperelliptic Jacobians with large Galois action on 2-torsion.
URL:https://www.math.ens.psl.eu/evenement/brauer-groups-and-the-brauer-manin-sets-of-kummer-varieties/
LOCATION:ENS Salle W
CATEGORIES:Variétés rationnelles
END:VEVENT
END:VCALENDAR