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X-WR-CALDESC:évènements pour Département de mathématiques et applications
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TZID:Europe/Paris
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TZNAME:CEST
DTSTART:20180325T010000
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TZOFFSETTO:+0100
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DTSTART:20181028T010000
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DTSTART:20190331T010000
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DTSTART:20191027T010000
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BEGIN:VEVENT
DTSTART;TZID=Europe/Paris:20190618T140000
DTEND;TZID=Europe/Paris:20190618T170000
DTSTAMP:20260421T183450
CREATED:20190618T120000Z
LAST-MODIFIED:20211104T135150Z
UID:8513-1560866400-1560877200@www.math.ens.psl.eu
SUMMARY:Après-midi de théorie de groupes
DESCRIPTION:14.00-14.45 Katrin Tent (Munster)\, Burnside groups of relatively small odd exponent15.00-15.45 Arindam Biswas (Vienne)\, On minimal complements in groups16.15-16.45 Laurent Bartholdi (Institut d’études avancées\, ENS Lyon)\, Dimension series and homotopy groups of spheres
URL:https://www.math.ens.psl.eu/evenement/apres-midi-de-theorie-de-groupes-4/
LOCATION:IHP salle 1
CATEGORIES:Séminaire de théorie des groupes à l’ENS
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Europe/Paris:20190514T140000
DTEND;TZID=Europe/Paris:20190514T170000
DTSTAMP:20260421T183450
CREATED:20190514T120000Z
LAST-MODIFIED:20211104T135214Z
UID:8510-1557842400-1557853200@www.math.ens.psl.eu
SUMMARY:Après-midi de théorie de groupes
DESCRIPTION:14.00-14.45 Stefan Witzel (Ecole Polytehchnique)15.00-15.45 Katie Vokes (IHES)15.45-16.15 coffee break16.15-16.45 Adrien Le Boudec (ENS Lyon)Stefan Witzel\, Arithmetic approximate groups and their finiteness propertiesI will talk about approximate groups\, a geometric generalization of groups. Approximate groups were discovered independently in various contexts and I will describe how they arise very naturally in the context of arithmetic groups. I will then explain how to extend topological finiteness properties of groups to approximate groups. This allows to make a connection betweenarithmetic groups in positive characteristic and arithmetic approximate groups in characteristic zero. The talk is based on joint work with Tobias Hartnick.Katie Vokes\, Hierarchical hyperbolicity of graphs associated to surfacesIn a paper of 2000\, Masur and Minsky studied the geometry of mapping class groups of surfaces using projections to certain Gromov hyperbolic graphs (the curve graphs) associated to subsurfaces. This inspired the definition by Behrstock\, Hagen and Sisto of hierarchically hyperbolic spaces\, which are equipped with similar projection maps\, satisfying conditions which guarantee a structure analogous to that of the mapping class group. I will give some background on these concepts and present a result demonstrating that a large family of graphs associated to surfaces are hierarchically hyperbolic spaces.Adrien Le Boudec\, Simple groups having a wreath product as a geometric modelThe goal of the talk will be to describe groups that are finitelygenerated\, simple\, and that act properly and cocompactly on thenatural Cayley graph of the wreath product A wr F\, where A is afinite group and F a non-abelian free group.
URL:https://www.math.ens.psl.eu/evenement/apres-midi-de-theorie-de-groupes-3/
LOCATION:Salle W (DMA)
CATEGORIES:Séminaire de théorie des groupes à l’ENS
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Europe/Paris:20190510T160000
DTEND;TZID=Europe/Paris:20190510T173000
DTSTAMP:20260421T183450
CREATED:20190510T140000Z
LAST-MODIFIED:20211104T132132Z
UID:8507-1557504000-1557509400@www.math.ens.psl.eu
SUMMARY:Non-archimedean and motivic integrals on the Hitchin fibration
DESCRIPTION:Based on mirror symmetry considerations\, Hausel and Thaddeus conjectured an equality between `stringy’ Hodge numbers for moduli spaces of SL_n/PGL_n Higgs bundles. With Michael Groechenig and Paul Ziegler we prove this conjecture using non-archimedean integrals on these moduli spaces\, building on work of Denef-Loeser and Batyrev. Similar ideas also lead to a new proof of the geometric stabilization theorem for anisotropic Hitchin fibers\, a key ingredient in the proof of the fundamental lemma by Ngô.In my talk I will outline the main arguments of the proofs and discuss the adjustments needed\, in order to replace non-archimedean integrals by motivic ones. The latter is joint work with François Loeser.
URL:https://www.math.ens.psl.eu/evenement/non-archimedean-and-motivic-integrals-on-the-hitchin-fibration/
LOCATION:ENS Salle W
CATEGORIES:Séminaire Géométrie et théorie des modèles
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Europe/Paris:20190510T141500
DTEND;TZID=Europe/Paris:20190510T154500
DTSTAMP:20260421T183450
CREATED:20190510T121500Z
LAST-MODIFIED:20211104T141516Z
UID:8509-1557497700-1557503100@www.math.ens.psl.eu
SUMMARY:Point-wise surjective presentations of stacks\, or why I am not afraid of (infinity) stacks anymore
DESCRIPTION:Any algebraic stack X can be represented by a groupoid object in the category of schemes: that is\, a pair of schemes Ob\, Mor and morphisms source\, target: Mor → Ob\, inversion: Mor → Mor\, composition: Mor ×_{Ob} Mor → Mor and identity: Ob → Mor that satisfy certain axioms. Yet this description of the stack X might be misleading.\nNamely\, given a field F which is not algebraically closed\, we have a natural functor between the groupoid (Ob(F)\,Mor(F)) and the groupoid X(F). While this functor is fully faithful\, it is often not essentially surjective.\nIn joint work with Nir Avni (in progress) we show that any algebraic groupoid has a presentation such that this functor will be essentially surjective for many fields (and under some assumptions on the stack\, for any field). The results are also extended to Henselian rings.\nDespite the title\, the talk will be about usual stacks and not infinity-stacks\, yet in some of the proofs it is more convenient to use the language of higher categories and I’ll try to explain why.\nNo prior knowledge of infinity stacks will be assumed\, but a superficial acquaintance with usual stacks will be helpful.
URL:https://www.math.ens.psl.eu/evenement/point-wise-surjective-presentations-of-stacks-or-why-i-am-not-afraid-of-infinity-stacks-anymore/
LOCATION:ENS Salle W
CATEGORIES:Séminaire Géométrie et théorie des modèles
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Europe/Paris:20190510T110000
DTEND;TZID=Europe/Paris:20190510T123000
DTSTAMP:20260421T183450
CREATED:20190510T090000Z
LAST-MODIFIED:20211025T103641Z
UID:8511-1557486000-1557491400@www.math.ens.psl.eu
SUMMARY:Almost strongly minimal ample geometries
DESCRIPTION:The notion of ampleness captures essential properties of projective spaces over fields. It is natural to ask whether any sufficiently ample strongly minimal set arises from an algebraically closed field. In this talk I will explain the question and present recent results on ample strongly minimal structures.
URL:https://www.math.ens.psl.eu/evenement/almost-strongly-minimal-ample-geometries/
CATEGORIES:Séminaire Géométrie et théorie des modèles
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Europe/Paris:20190507T160000
DTEND;TZID=Europe/Paris:20190507T173000
DTSTAMP:20260421T183450
CREATED:20190507T140000Z
LAST-MODIFIED:20211104T140929Z
UID:8508-1557244800-1557250200@www.math.ens.psl.eu
SUMMARY:Groups definable in Presburger arithmetic
DESCRIPTION:I will give a complete description of all groups definable in Presburger arithmetic\, up to finite index subgroups. This builds on previous work on bounded groups in Presburger arithmetic by Mariana Vicaria and Alf Onshuus.
URL:https://www.math.ens.psl.eu/evenement/groups-definable-in-presburger-arithmetic/
LOCATION:Sophie Germain salle 2015
CATEGORIES:Théorie des Modèles et Groupes
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Europe/Paris:20190416T140000
DTEND;TZID=Europe/Paris:20190416T170000
DTSTAMP:20260421T183450
CREATED:20190416T120000Z
LAST-MODIFIED:20211119T102741Z
UID:8506-1555423200-1555434000@www.math.ens.psl.eu
SUMMARY:Après-midi de théorie des groupes
DESCRIPTION:14.00 -14.45 Cornelia Drutu (Oxford)\, Fixed point properties and conformal dimension of the boundary for hyperbolic groups\n15.00- 15-45 Mathieu Dussaule (Nantes)\, The Guivarch inequality in relatively hyperbolic groups\n15.45-16.15 coffee break\,\n16.15-17.00 Anthony Genevois (Orsay)\, Cubical geometry of braided Thompson’s group
URL:https://www.math.ens.psl.eu/evenement/apres-midi-de-theorie-des-groupes-6/
LOCATION:Salle W (Toits du DMA)
CATEGORIES:Séminaire de théorie des groupes à l’ENS
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Europe/Paris:20190406T160000
DTEND;TZID=Europe/Paris:20190406T173000
DTSTAMP:20260421T183450
CREATED:20190406T140000Z
LAST-MODIFIED:20211104T122042Z
UID:14060-1554566400-1554571800@www.math.ens.psl.eu
SUMMARY:Computability\, orders\, and groups
DESCRIPTION:Orderable groups are extensively studied by logicians and group theorists. In my talk I will address aspects of left- or bi-orderable groups that are connected with computability theory. In particular\, I will talk about constructions of bi-orderable computable groups that cannot be embedded into groups with computable bi-order. I will also discuss our recent work in progress with M. Steenbock about simplicity and computably left-orderability.
URL:https://www.math.ens.psl.eu/evenement/computability-orders-and-groups-2/
LOCATION:Sophie Germain\, salle 2015
CATEGORIES:Théorie des Modèles et Groupes
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Europe/Paris:20190322T160000
DTEND;TZID=Europe/Paris:20190322T173000
DTSTAMP:20260421T183450
CREATED:20190322T150000Z
LAST-MODIFIED:20211104T141546Z
UID:8505-1553270400-1553275800@www.math.ens.psl.eu
SUMMARY:Patching over Berkovich Curves
DESCRIPTION:Patching was first introduced as an approach to the Inverse Galois Problem. The technique was then extended to a more algebraic setting and used to prove a local-global principle by D. Harbater\, J. Hartmann and D. Krashen. I will present an adaptation of the method of patching to the setting of Berkovich analytic curves. This will then be used to prove a local-global principle for function fields of curves that generalizes that of the above mentioned authors.
URL:https://www.math.ens.psl.eu/evenement/patching-over-berkovich-curves/
LOCATION:ENS Salle W
CATEGORIES:Séminaire Géométrie et théorie des modèles
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Europe/Paris:20190322T000000
DTEND;TZID=Europe/Paris:20190322T000000
DTSTAMP:20260421T183450
CREATED:20190321T230000Z
LAST-MODIFIED:20211104T112226Z
UID:8501-1553212800-1553212800@www.math.ens.psl.eu
SUMMARY:Independence of CM points in elliptic curves
DESCRIPTION:I will speak about joint work with Jacob Tsimerman. Let E be an elliptic curve parameterized by a modular (or Shimura) curve. There are a number of results (…\, Buium-Poonen\, Kuhne) to the effect that the images of CM points are (under suitable hypotheses) linearly independent in E. We consider this issue in the setting of the Zilber-Pink conjecture and prove a result which improves previous results in some aspects
URL:https://www.math.ens.psl.eu/evenement/independence-of-cm-points-in-elliptic-curves/
LOCATION:ENS Salle W
CATEGORIES:Séminaire Géométrie et théorie des modèles
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Europe/Paris:20190322T000000
DTEND;TZID=Europe/Paris:20190322T000000
DTSTAMP:20260421T183450
CREATED:20190321T230000Z
LAST-MODIFIED:20211104T112227Z
UID:8502-1553212800-1553212800@www.math.ens.psl.eu
SUMMARY:Counting rational points with the determinant method
DESCRIPTION:The determinant method gives upper bounds for the number of rational points of bounded height on or near algebraic varieties defined over global fields. There is a real-analytic version of the method due to Bombieri and Pila and a p-adic version due to Heath-Brown. The aim of our talk is to describe a global refinement of the p-adic method and some applications like a uniform bound for non-singular cubic curves which improves upon earlier bounds of Ellenberg-Venkatesh and Heath-Brown.
URL:https://www.math.ens.psl.eu/evenement/counting-rational-points-with-the-determinant-method/
LOCATION:ENS Salle W
CATEGORIES:Séminaire Géométrie et théorie des modèles
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Europe/Paris:20190319T160000
DTEND;TZID=Europe/Paris:20190319T173000
DTSTAMP:20260421T183450
CREATED:20190319T150000Z
LAST-MODIFIED:20211104T112241Z
UID:8504-1553011200-1553016600@www.math.ens.psl.eu
SUMMARY:The word and conjugacy problems in finitely generated groups
DESCRIPTION:The word and conjugacy problems are central decision problems associated with finitely generated groups. In particular\, there are deep results which bridge some of the main concepts of the theories of computability and computational complexity with group theoretical invariants through the word problem in groups. In this talk I will recall some of the well-known facts about the word and conjugacy problems in groups as well as discuss new results concerning the relationship between them.
URL:https://www.math.ens.psl.eu/evenement/the-word-and-conjugacy-problems-in-finitely-generated-groups/
LOCATION:Sophie Germain salle 2015
CATEGORIES:Théorie des Modèles et Groupes
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Europe/Paris:20190312T160000
DTEND;TZID=Europe/Paris:20190312T173000
DTSTAMP:20260421T183450
CREATED:20190312T150000Z
LAST-MODIFIED:20211104T112241Z
UID:8503-1552406400-1552411800@www.math.ens.psl.eu
SUMMARY:Density of compressiblity in NIP theories
DESCRIPTION:Joint with Itay Kaplan and Pierre Simon.Distal theories are NIP theories which are ?Roewholly unstable?R. Chernikov and Simon’s ?Roestrong honest definitions?R characterise distal theories as those in which every type is compressible. Adapting recent work in machine learning of Chen\, Cheng\, and Tang on bounds on the ?Roerecursive teaching dimension?R of a finite concept class\, we find that compressibility is dense in NIP structures\, i.e. any formula can be completed to a compressible type in S(A). Considering compressibility as an isolation notion (which specialises to l-isolation in stable theories)\, we obtain consequences on the existence of models with certain properties.
URL:https://www.math.ens.psl.eu/evenement/density-of-compressiblity-in-nip-theories/
LOCATION:Sophie Germain salle 2015
CATEGORIES:Théorie des Modèles et Groupes
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Europe/Paris:20190312T140000
DTEND;TZID=Europe/Paris:20190312T170000
DTSTAMP:20260421T183450
CREATED:20190312T130000Z
LAST-MODIFIED:20211104T112225Z
UID:8498-1552399200-1552410000@www.math.ens.psl.eu
SUMMARY:Après-midi de théorie des groupes
DESCRIPTION:14.00-14.45  Emmanuel Militon (Nice)\, Groups of diffeomorphisms of a Cantor set15.00-15.45  Simon André (Rennes)\, Hyperbolicity is preserved under elementary equivalence15.45-16.15 coffee break(CANCELED) 16.15-17.00 Nikolay Nikolov (Oxford)\, On conjugacy classes in compact groups
URL:https://www.math.ens.psl.eu/evenement/apres-midi-de-theorie-des-groupes-4/
LOCATION:Salle W
CATEGORIES:Séminaire de théorie des groupes à l’ENS
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Europe/Paris:20190312T140000
DTEND;TZID=Europe/Paris:20190312T153000
DTSTAMP:20260421T183450
CREATED:20190312T130000Z
LAST-MODIFIED:20211104T112226Z
UID:8500-1552399200-1552404600@www.math.ens.psl.eu
SUMMARY:Strongly NIP almost real closed fields
DESCRIPTION:The following conjecture is due to Shelah–Hasson: Any infinite strongly NIP field is either real closed\, algebraically closed\, or admits a non-trivial definable henselian valuation\, in the language of rings. We specialise this conjecture to ordered fields in the language of ordered rings\, which leads towards a systematic study of the class of strongly NIP almost real closed fields. As a result\, we obtain a complete characterisation of this class.
URL:https://www.math.ens.psl.eu/evenement/strongly-nip-almost-real-closed-fields/
LOCATION:Sophie Germain salle 1016
CATEGORIES:Théorie des Modèles et Groupes
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Europe/Paris:20190226T160000
DTEND;TZID=Europe/Paris:20190226T173000
DTSTAMP:20260421T183450
CREATED:20190226T150000Z
LAST-MODIFIED:20211104T112029Z
UID:8497-1551196800-1551202200@www.math.ens.psl.eu
SUMMARY:Uncountable categoricity of structures based on Banach spaces
DESCRIPTION:A continuous theory T of bounded metric structures is said to be kappa-categorical if T has a unique model of density kappa. Work of Ben Yaacov and Shelah+Usvyatsov shows that Morley’s Theorem holds in this context: if T has a countable signature and is kappa-categorical for some uncountable kappa\, then T is kappa-categorical for all uncountable kappa. In classical (discrete) model theory\, there are several characterizations of uncountable categoricity. For example\, there is a structure theorem for uncountably categorical theories T\, due to Baldwin+Lachlan: there is a strongly minimal set D defined over the prime model of T such that every uncountable model M of T is minimal and prime over D(M). Moreover (and easier)\, if T has such a strongly minimal set\, then T is uncountably categorical.In the more general metric structure setting\, nothing remotely like this is known. Indeed\, the metric analog of a strongly minimal set is nowhere to be seen\, at the moment. If one restricts attention to metric structures based on (unit balls) of Banach structures\, more is known. The appropriate analog of strongly minimal sets seems to be the unit balls of Hilbert spaces. After the speaker called attention to this phenomenon in some examples from functional analysis\, Shelah and Usvyatsov investigated it and proved a remarkable result (arxiv 1402.6513
URL:https://www.math.ens.psl.eu/evenement/uncountable-categoricity-of-structures-based-on-banach-spaces/
LOCATION:Sophie Germain salle 2015
CATEGORIES:Théorie des Modèles et Groupes
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Europe/Paris:20190219T160000
DTEND;TZID=Europe/Paris:20190219T173000
DTSTAMP:20260421T183450
CREATED:20190219T150000Z
LAST-MODIFIED:20211104T112028Z
UID:8496-1550592000-1550597400@www.math.ens.psl.eu
SUMMARY:On the theory of rigid meromorphic functions in positive characteristic
DESCRIPTION:There is a well-known analogy between the arithmetic of rational numbers and the theory of meromorphic functions over a normed field. It is a classical result of Julia Robinson that the first order theory of the field of rational numbers is undecidable\, and one would expect such a result in the meromorphic setting. In this talk I’ll give an outline of the proof of undecidability for rigid meromorphic functions in positive characteristic
URL:https://www.math.ens.psl.eu/evenement/on-the-theory-of-rigid-meromorphic-functions-in-positive-characteristic/
LOCATION:Salle 2015 Sophie Germain
CATEGORIES:Théorie des Modèles et Groupes
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Europe/Paris:20190215T160000
DTEND;TZID=Europe/Paris:20190215T173000
DTSTAMP:20260421T183450
CREATED:20190215T150000Z
LAST-MODIFIED:20211104T111801Z
UID:8490-1550246400-1550251800@www.math.ens.psl.eu
SUMMARY:Definable subsets of a Berkovich curve
DESCRIPTION:Let k be an algebraically closed complete rank 1 non-trivially valued field. Let X be an algebraic curve over k and let X^an be its analytification in the sense of Berkovich. We functorially associate to X^an a definable set X^S in a natural language. As a corollary\, we obtain an alternative proof of a result of Hrushovski-Loeser about the iso-definability of curves. Our association being explicit allows us to provide a concrete description of the definable subsets of X^S: they correspond to radial sets. This is a joint work with Jérôme Poineau.
URL:https://www.math.ens.psl.eu/evenement/definable-subsets-of-a-berkovich-curve/
LOCATION:ENS Salle W
CATEGORIES:Séminaire Géométrie et théorie des modèles
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Europe/Paris:20190215T141500
DTEND;TZID=Europe/Paris:20190215T154500
DTSTAMP:20260421T183450
CREATED:20190215T131500Z
LAST-MODIFIED:20211104T111802Z
UID:8492-1550240100-1550245500@www.math.ens.psl.eu
SUMMARY:Tame topology and Hodge theory.
DESCRIPTION:I will explain how tame topology seems the natural setting for variational Hodge theory. As an instance I will sketch a new proof of the algebraicity of the components of the Hodge locus\, a celebrated result of Cattani-Deligne-Kaplan (joint work with Bakker and Tsimerman).
URL:https://www.math.ens.psl.eu/evenement/tame-topology-and-hodge-theory/
LOCATION:ENS Salle W
CATEGORIES:Séminaire Géométrie et théorie des modèles
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Europe/Paris:20190215T110000
DTEND;TZID=Europe/Paris:20190215T123000
DTSTAMP:20260421T183450
CREATED:20190215T100000Z
LAST-MODIFIED:20211104T111802Z
UID:8491-1550228400-1550233800@www.math.ens.psl.eu
SUMMARY:Unlikely intersections with E x CM curves in A_2
DESCRIPTION:The Zilber-Pink conjecture predicts that an algebraic curve in A_2 has only finitely many intersections with the special curves\, unless it is contained in a proper special subvariety.Under a large Galois orbits hypothesis\, we prove the finiteness of the intersection with the special curves parametrising abelian surfaces isogenous to the product of two elliptic curves\, at least one of which has complex multiplication. Furthermore\, we show that this large Galois orbits hypothesis holds for curves satisfying a condition on their intersection with the boundary of the Baily–Borel compactification of A_2.More generally\, we show that a Hodge generic curve in an arbitrary Shimura variety has only finitely many intersection points with the generic points of a so-called Hecke–facteur family\, again under a large Galois orbits hypothesis.This is a joint work with Martin Orr (University of Warwick).
URL:https://www.math.ens.psl.eu/evenement/unlikely-intersections-with-e-x-cm-curves-in-a_2/
LOCATION:ENS Salle W
CATEGORIES:Séminaire Géométrie et théorie des modèles
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Europe/Paris:20190212T140000
DTEND;TZID=Europe/Paris:20190212T170000
DTSTAMP:20260421T183450
CREATED:20190212T130000Z
LAST-MODIFIED:20211104T112225Z
UID:8499-1549980000-1549990800@www.math.ens.psl.eu
SUMMARY:Après-midi de théorie des groupes
DESCRIPTION:14.00-14.45 Joshua Frisch (Caltech) Proximal actions\, Strong amenability\, and Infinite conjugacy class groups15.00-15.45 Andy Zucker (Paris VII) Bernoulli Disjointness15.45-16.15 coffee break16.15-17.00 Christophe Garban (Université Lyon 1) Inverted orbits of exclusion processes\, diffuse-extensive-amenability and (non-?)amenability of the interval exchanges
URL:https://www.math.ens.psl.eu/evenement/apres-midi-de-theorie-des-groupes-5/
LOCATION:Salle W
CATEGORIES:Séminaire de théorie des groupes à l’ENS
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Europe/Paris:20190205T160000
DTEND;TZID=Europe/Paris:20190205T173000
DTSTAMP:20260421T183450
CREATED:20190205T150000Z
LAST-MODIFIED:20211104T111801Z
UID:8489-1549382400-1549387800@www.math.ens.psl.eu
SUMMARY:Groupes d'automorphismes et Propriété (T)
DESCRIPTION:Nous présenterons une preuve de la Propriété (T) de Kazhdan pour les groupes d’automorphismes de structures métriques aleph_0-catégoriques. Ceci généralise des résultats précédents de Bekka (pour le groupe unitaire) et de Evans et Tsankov (pour les groupes pro-oligomorphes)\, sans besoin de faire appel à des résultats de classification de représentations unitaires. En effet\, l’argument est purement modèle-théorique et basé sur des principes de la stabilité locale.
URL:https://www.math.ens.psl.eu/evenement/groupes-dautomorphismes-et-propriete-t/
LOCATION:Sophie Germain salle 2015
CATEGORIES:Théorie des Modèles et Groupes
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Europe/Paris:20190129T160000
DTEND;TZID=Europe/Paris:20190129T173000
DTSTAMP:20260421T183450
CREATED:20190129T150000Z
LAST-MODIFIED:20211104T111800Z
UID:8488-1548777600-1548783000@www.math.ens.psl.eu
SUMMARY:Spectrum of the profinite completion of the integers
DESCRIPTION:Using ultraproducts\, I will describe the spectrum of the profinite completion of the integers and of the finite adeles over the rationals.The final aim is to describe the structure sheaf of these structures.Joint work with Margarita Otero and Angus Macintyre.
URL:https://www.math.ens.psl.eu/evenement/spectrum-of-the-profinite-completion-of-the-integers/
LOCATION:Sophie Germain salle 1016
CATEGORIES:Théorie des Modèles et Groupes
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Europe/Paris:20190122T140000
DTEND;TZID=Europe/Paris:20190122T170000
DTSTAMP:20260421T183450
CREATED:20190122T130000Z
LAST-MODIFIED:20211104T111601Z
UID:8486-1548165600-1548176400@www.math.ens.psl.eu
SUMMARY:Après-midi de théorie des groupes
DESCRIPTION:Tuesday\, 22 January14.00-14.45 Bertrand Rémy (Ecole Polytechnique)15.00-15.45 Tom Hutchcroft (Cambridge)15.45-16.15 coffee break16.15-17.00 Pavel Zalesski (University of Brasilia)Bertrand Remy\, Quasi-isometric invariance of continuous group Lp-cohomology\, and first applications to vanishings (joint with Marc Bourdon)We show that the continuous L^p-cohomology of locally compact second countable groups is a quasi-isometric invariant. As an application\, we prove partial results supporting a positive answer to a question asked by M. Gromov\, suggesting a classical behaviour of continuous L^p-cohomology of simple real Lie groups. In addition to quasi-isometric invariance\, the ingredients are a spectral sequence argument and Pansu?RTMs vanishing results for real hyperbolic spaces. In the best adapted cases of simple Lie groups\, we obtain nearly half of the relevant vanishings. Tom Hutchcroft\, Kazhdan groups have cost 1I will sketch a proof that Kazhdan groups have cost 1\, answering a question of Gaboriau. No knowledge of Kazhdan groups or of cost will be assumed. Joint work with Gabor Pete.Pavel Zalesski\, The profinite completion of 3-manifold groups.Abstract. We shall present structural results of the profinite completion widehat G of a 3-manifold group G and its interrelation with the structure of G. We shall address the question to what extent the profinite completion of the fundamental group $pi_1M of a 3-manifold determines the manifold M and discuss residual properties of pi_1 M.
URL:https://www.math.ens.psl.eu/evenement/apres-midi-de-theorie-des-groupes-3/
LOCATION:Salle W ENS
CATEGORIES:Séminaire de théorie des groupes à l’ENS
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BEGIN:VEVENT
DTSTART;TZID=Europe/Paris:20190115T160000
DTEND;TZID=Europe/Paris:20190115T173000
DTSTAMP:20260421T183450
CREATED:20190115T150000Z
LAST-MODIFIED:20211104T111400Z
UID:8481-1547568000-1547573400@www.math.ens.psl.eu
SUMMARY:Density of the union of Cartan subgroups of  o-minimal groups
DESCRIPTION:Let G be a group. A subgroup H of G is a Cartan subgroup  ofG if H is a maximal nilpotent subgroup of G\, and for every normal finiteindex subgroup X of H\, X has finite index in its normalizer in G. \nWe consider Cartan subgroups of  definably connect groups definable inan o-minimal structure. In [BJ0] we proved that\, in this context\,Cartan subgroups of G exist\, they are definable and they fall infinitely many conjugacy classes. \nIn this talk I will prove that the union of the Cartan subgroups isdense in the group\, which was the main question left open in [BBO].(Joint work with Elías Baro and Alessandro Berarducci.) \n [BJ0] E.Baro\, E. Jaligot and M.Otero. Cartan subgroups of groupsdefinable in o-minimal structures\, J. Inst. Math. Juissieu 13 no. 4(2014) 849 – 893.
URL:https://www.math.ens.psl.eu/evenement/density-of-the-union-of-cartan-subgroups-of-o-minimal-groups/
LOCATION:Sophie Germain salle 2015
CATEGORIES:Théorie des Modèles et Groupes
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Europe/Paris:20190111T160000
DTEND;TZID=Europe/Paris:20190111T173000
DTSTAMP:20260421T183450
CREATED:20190111T150000Z
LAST-MODIFIED:20211104T111600Z
UID:8484-1547222400-1547227800@www.math.ens.psl.eu
SUMMARY:Tame open core and small groups in pairs of topological geometric structures
DESCRIPTION:Using the group configuration theorem\, Hrushovski and Pillay showed that the law of a group definable in the reals or the p-adics is locally an algebraic group law\, up to definable isomorphism. There are some natural expansions of these two theories of fields\, by adding a predicate for a dense substructure\, for example the algebraic reals or the algebraic p-adics. We will present an overview on some of the features of these expansions\, and particularly on the characterisation of open definable sets as well as of groups definable in the pairs.
URL:https://www.math.ens.psl.eu/evenement/tame-open-core-and-small-groups-in-pairs-of-topological-geometric-structures/
LOCATION:ENS Salle W
CATEGORIES:Séminaire Géométrie et théorie des modèles
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Europe/Paris:20190111T141500
DTEND;TZID=Europe/Paris:20190111T154500
DTSTAMP:20260421T183450
CREATED:20190111T131500Z
LAST-MODIFIED:20211104T111400Z
UID:8482-1547216100-1547221500@www.math.ens.psl.eu
SUMMARY:Definability in the infinitesimal subgroup of a simple compact Lie group
DESCRIPTION:Joint work with Kobi Peterzil.Let G be a simple compact Lie group\, for example G=SO_3(R). We consider the structure of definable sets in the subgroup G^{00} of infinitesimal elements. In an aleph_0-saturated elementary extension of the real field\, G^{00} is the inverse image of the identity under the standard part map\, so is definable in the corresponding valued field. We show that the pure group structure on G^{00} recovers the valued field\, making this a bi-interpretation. Hence the definable sets in the group are as rich as possible.
URL:https://www.math.ens.psl.eu/evenement/definability-in-the-infinitesimal-subgroup-of-a-simple-compact-lie-group/
LOCATION:ENS Salle W
CATEGORIES:Séminaire Géométrie et théorie des modèles
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Europe/Paris:20190111T110000
DTEND;TZID=Europe/Paris:20190111T123000
DTSTAMP:20260421T183450
CREATED:20190111T100000Z
LAST-MODIFIED:20211104T111559Z
UID:8483-1547204400-1547209800@www.math.ens.psl.eu
SUMMARY:Scrollar invariants\, resolvents\, and syzygies
DESCRIPTION:With every cover C -> P^1 of the projective line one can associate its so-called scrollar invariants (also called Maroni invariants) which describe how the push-forward of the structure sheaf of C splits over P^1. They can be viewed as geometric counterparts of the successive minima of the lattice associated with the ring of integers of a number field. In this talk we consider the following problem: how do the scrollar invariants of the Galois closure C’ -> P^1 and of its various subcovers (the so-called resolvents of C -> P^1) relate to known invariants of the given cover? This concerns ongoing work with Yongqiang Zhao\, in which we put a previous observation for covers of degree 4 due to Casnati in a more general framework. As we will see the answer involves invariants related to syzygies that were introduced by Schreyer. As time permits\, we will discuss a number-theoretic manifestation of the phenomena observed.
URL:https://www.math.ens.psl.eu/evenement/scrollar-invariants-resolvents-and-syzygies/
LOCATION:ENS Salle W
CATEGORIES:Séminaire Géométrie et théorie des modèles
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Europe/Paris:20190110T160000
DTEND;TZID=Europe/Paris:20190110T173000
DTSTAMP:20260421T183450
CREATED:20190110T150000Z
LAST-MODIFIED:20211104T112500Z
UID:14063-1547136000-1547141400@www.math.ens.psl.eu
SUMMARY:Sous-groupes qui pavent génériquement et géométrie des involutions
DESCRIPTION:(En collaboration avec Joshua Wiscons)L’exposé mélange théorie des modèles\, théorie des groupes\, et algèbre géométrique. On y parlera de groupes de rang de Morley fini\, mais il suffit de savoir naïvement ce qu’est une dimension à valeurs entières\, sans devoir maîtriser les finesses de la conjecture de Cherlin-Zilber.Un groupe abstrait porte peu d’information de nature géométrique\, même au sens des géométries d’incidence\, et c’est toujours remarquable si cela se produit.Le pur groupe SO(3\,R)\, par exemple\, permet de redéfinir l’espace projectif réel. PGL(2\,C) permet presque la même chose : il définit un fragment générique de l’espace projectif complexe. En fait cette situation est naturellement liée à la distribution des involutions et aux intersections entre conjugués de leur centralisateur\, qui pavent génériquement le groupe ambiant (tout cela sera expliqué dans SO(3\,R) et PGL(2\,C)).En suivant cette piste on peut obtenir des énoncés étonnamment forts\, généralisant au passage divers classiques sur les mauvais groupes ou sur les groupes définissablement linéaires de rang de Morley fini. On conjecture également que cette géométrie des involutions annonce un nouveau théorème d’identification pour PGL(2\, K).
URL:https://www.math.ens.psl.eu/evenement/sous-groupes-qui-pavent-generiquement-et-geometrie-des-involutions-2/
CATEGORIES:Théorie des Modèles et Groupes
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Europe/Paris:20181218T160000
DTEND;TZID=Europe/Paris:20181218T173000
DTSTAMP:20260421T183450
CREATED:20181218T150000Z
LAST-MODIFIED:20211104T111158Z
UID:8475-1545148800-1545154200@www.math.ens.psl.eu
SUMMARY:Les groupes virtuellement libres sont presque homogènes
DESCRIPTION:Perin et Sklinos\, et indépendamment Ould Houcine\, ont démontré en 2011 que les groupes libres sont homogènes : deux éléments qui ont le même type sont dans la même orbite sous l’action du groupe d’automorphismes. Dans cet exposé\, j’expliquerai que ce résultat reste presque vrai pour les groupes virtuellement libres\, au sens suivant : l’ensemble des éléments ayant le même type qu’un élément donné contient un nombre fini d’orbites sous le groupe d’automorphismes\, et ce nombre ne dépend pas de l’élément considéré. J’expliquerai également pourquoi je pense que ce résultat est optimal\, en donnant un exemple de groupe virtuellement libre dont je conjecture qu’il n’est pas homogène (travail en cours).
URL:https://www.math.ens.psl.eu/evenement/les-groupes-virtuellement-libres-sont-presque-homogenes/
LOCATION:Sophie Germain salle 2015
CATEGORIES:Théorie des Modèles et Groupes
END:VEVENT
END:VCALENDAR