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X-WR-CALDESC:Évènements pour Laboratoire de Mathématiques de Versailles
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BEGIN:VEVENT
DTSTART;TZID=Europe/Paris:20210302T113000
DTEND;TZID=Europe/Paris:20210302T123000
DTSTAMP:20260406T030004
CREATED:20210118T120926Z
LAST-MODIFIED:20210303T094935Z
UID:8911-1614684600-1614688200@lmv.math.cnrs.fr
SUMMARY:PS : Céline Duval (Univ. Paris Descartes) Total variation distance for discretely observed Lévy processes: a Gaussian approximation of the small jumps
DESCRIPTION:It is common to treat small jumps of Lévy processes as Wiener noise and to approximate its marginals by a Gaussian distribution. However\, results that allow to quantify the goodness of this approximation according to a given metric are rare. We study what happens when the chosen metric is the total variation distance. Such a choice is motivated by its statistical interpretation ; if the total variation distance between two statistical models converges to zero\, then no test can be constructed to distinguish the two models and they are therefore asymptotically equally informative. We provide a Gaussian approximation for the small jumps of Lévy processes in total variation distance. Non-asymptotic bounds for the total variation distance between $n$ discrete observations of small jumps of a Lévy process and the corresponding Gaussian distribution are given. (Joint work with A. Carpentier et E. Mariucci)
URL:https://lmv.math.cnrs.fr/evenenement/ps-celine-duval-univ-paris-descartes-titre-a-venir/
CATEGORIES:Séminaire PS
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Europe/Paris:20210302T113000
DTEND;TZID=Europe/Paris:20210302T123000
DTSTAMP:20260406T030004
CREATED:20210214T100313Z
LAST-MODIFIED:20220422T120604Z
UID:8976-1614684600-1614688200@lmv.math.cnrs.fr
SUMMARY:AG : Max Gurevich (Technion - Israel Institute of Technology ) : "New constructions for irreducible representations in monoidal categories of type A"
DESCRIPTION:Abstract: \nEver since the classical theory of a highest-weight classification\, one ever-present strength of Lie theory\, was its ability to produce effective and elegant descriptions of collections of simple objects in categories of interest. A cornerstone feat achieved by Zelevinsky in that regard\, was the combinatorial explication of the Langlands classification for smooth irreducible representations of p-adic GL_n. It was a forerunner for an exploration of similar classifications for various categories of similar nature\, such as modules over affine Hecke algebras or quantum affine algebras\, to name a few. Yet\, throughout these settings\, a systematic understanding of the nature of reducible finite-length representations remains largely out of grasp. \nRecently\, joint with Erez Lapid\, we have revisited the Zelevinsky setting by suggesting a refined construction of all irreducible representations\,with the hope of shedding light on standing decomposition problems. This construction applies the Robinson-Schensted-Knuth algorithm\, while categorifying the determinantal Doubilet-Rota-Stein basis for matrix polynomial rings appearing in invariant theory. \nIn this talk I would like to introduce the new construction into the setting of modules over quiver Hecke (KLR) algebras. In type A\, this category may be viewed as a quantization/gradation of the category of representations of p-adic groups. I will explain how adopting the new point of view and exploiting recent developments in the subject (such as the normal sequence notion of Kashiwara-Kim) brings some conjectural properties of the RSK construction (back in the p-adic setting) into resolution. \n[ L’exposé aura lieu en ligne\, sur Zoom. Pour recevoir le lien de connection\, contacter l’organisateur LP] \nVidéo et slides de l’exposé.
URL:https://lmv.math.cnrs.fr/evenenement/expose-de-max-gurevich-technion-israel-institute-of-technology/
CATEGORIES:Séminaire AG
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Europe/Paris:20210309T113000
DTEND;TZID=Europe/Paris:20210309T123000
DTSTAMP:20260406T030004
CREATED:20210301T090812Z
LAST-MODIFIED:20210311T154141Z
UID:8999-1615289400-1615293000@lmv.math.cnrs.fr
SUMMARY:AG : Olivier Brunat (IMJ-PRG) : Ensembles basiques et unitriangularité I
DESCRIPTION:Résumé : Dans cet exposé\, j’introduirai la notion d’ensemble basique unitriangulaire et essayerai de motiver leur utilité en théorie des représentations modulaires des groupes finis. Je présenterai également quelques résultats récents obtenus sur le sujet en collaboration avec Gramain-Jacon\, et avec Dudas-Taylor. \n[ L’exposé aura lieu en ligne\, sur Zoom. Pour recevoir le lien de connection\, contacter l’organisateur LP]
URL:https://lmv.math.cnrs.fr/evenenement/ag-olivier-brunat-imj-prg/
CATEGORIES:Séminaire AG
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Europe/Paris:20210311T110000
DTEND;TZID=Europe/Paris:20210311T123000
DTSTAMP:20260406T030004
CREATED:20210217T142928Z
LAST-MODIFIED:20210311T154135Z
UID:8978-1615460400-1615465800@lmv.math.cnrs.fr
SUMMARY:CRYPTO : Antonin Leroux (Inria Saclay) : SQISign: Compact Post-Quantum Signature from Quaternions and Isogenies
DESCRIPTION:We introduce a new signature scheme\, SQISign\, (for Short Quaternion and Isogeny Signature)  from isogeny graphs of supersingular elliptic curves. The signature scheme is derived from a new one-round\, high soundness\, interactive identification protocol. Targeting the post-quantum NIST-1 level of security\, our implementation results in signatures of 204 bytes\, secret keys of 16 bytes and public keys of 64 bytes. In particular\, the signature and public key sizes combined are an order of magnitude smaller than all other post-quantum signature schemes. On a modern workstation\, our implementation in C takes 0.6s for key generation\, 2.5s for signing\, and 50ms for verification.\nWhile the soundness of the identification protocol follows from classical assumptions\, the zero-knowledge property relies on the second main contribution of this paper.\nWe introduce a new algorithm to find an isogeny path connecting two given supersingular elliptic curves of known endomorphism rings.\nA previous algorithm to solve this problem\, due to Kohel\, Lauter\, Petit and Tignol\, systematically reveals paths from the input curves to a `special’ curve. This leakage would break the zero-knowledge property of the protocol. Our algorithm does not directly reveal such a path\, and subject to a new computational assumption\, we prove that the resulting identification protocol is zero-knowledge.
URL:https://lmv.math.cnrs.fr/evenenement/crypto-antonin-leroux-inria-saclay-sqisign-compact-post-quantum-signature-from-quaternions-and-isogenies/
LOCATION:Bâtiment Descartes\, salle 301
CATEGORIES:Séminaire CRYPTO
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Europe/Paris:20210316T113000
DTEND;TZID=Europe/Paris:20210316T123000
DTSTAMP:20260406T030004
CREATED:20210118T121214Z
LAST-MODIFIED:20210318T102953Z
UID:8913-1615894200-1615897800@lmv.math.cnrs.fr
SUMMARY:PS : Ester Mariucci (LMV) Nonparametric estimation of the Lévy density from high frequency observations
DESCRIPTION:Résumé : \nWe consider the problem of estimating the Lévy density $f$ of a pure jump Lévy process\, possibly of infinite variation\, from the high frequency observation of one trajectory. We discuss two different approaches. \nThe first one consists in reducing the problem of the nonparametric estimation of $f$ to an easier one\, namely the estimation of a drift of a Gaussian white noise model. \nMore precisely\, we establish a global asymptotic equivalence between the experiments generated by the discrete (high frequency) or continuous observation of a path of a Lévy process and a Gaussian white noise experiment observed up to a time $T$\, with $T$ tending to $\infty$. These approximations are given in the sense of the Le Cam distance\, under some smoothness conditions on the unknown Lévy density. The asymptotic equivalences are established by constructing explicit equivalence mappings that can be used to reproduce one experiment from the other and to transfer estimators. \nThe second approach consists in directly constructing an estimator of the Lévy density. For that we use a compound Poisson approximation and we build a linear wavelet estimator. Its performance is studied in terms of $L_p$ loss functions\, $p\geq1$\, over Besov balls. The resulting rates are minimax-optimal for a large class of Lévy processes. \nTravail en collaboration avec Céline Duval (MAP5\, Paris). \nExposé en mode hybride  : oratrice et partie du public au LMV + retransmission en visio (lien Zoom sur demande) \n 
URL:https://lmv.math.cnrs.fr/evenenement/ps-ester-mariucci-lmv-nonparametric-estimation-of-the-levy-density-from-high-frequency-observations/
CATEGORIES:Séminaire PS
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Europe/Paris:20210316T113000
DTEND;TZID=Europe/Paris:20210316T123000
DTSTAMP:20260406T030004
CREATED:20210301T091039Z
LAST-MODIFIED:20220422T120807Z
UID:9001-1615894200-1615897800@lmv.math.cnrs.fr
SUMMARY:AG: Olivier Dudas (IMJ-PRG) : Ensembles basiques et unitriangularité II : le cas des groupes réductifs finis
DESCRIPTION:Résumé : Dans cet exposé je parlerai des matrices de décomposition pour les groupes réductifs finis tels que GL(n\,q)\, Sp(2n\,q)\, SO(n\,q)… J’expliquerai quels sont les caractères à considérer pour obtenir un ensemble basique et pourquoi ils permettent de mettre la matrice de décomposition sous forme unitriangulaire (résultat obtenu avec O. Brunat et J. Taylor). J’illustrerai ces résulats dans l’exemple de GL(n\,q) en insistant sur le lien entre les représentations du groupe symétrique\, les caractères unipotents de GL(n\,q) et la géométrie des classes unipotentes du groupe algébrique GL(n). \n[ L’exposé aura lieu en ligne\, sur Zoom. Pour recevoir le lien de connection\, contacter l’organisateur LP] \nSlides de l’exposé.
URL:https://lmv.math.cnrs.fr/evenenement/ag-olivier-dudas-imj-prg/
CATEGORIES:Séminaire AG
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Europe/Paris:20210323T113000
DTEND;TZID=Europe/Paris:20210323T123000
DTSTAMP:20260406T030004
CREATED:20210301T091354Z
LAST-MODIFIED:20220422T121156Z
UID:9003-1616499000-1616502600@lmv.math.cnrs.fr
SUMMARY:AG : Enrica Mazzon (MPIM-Bonn) : "Toric geometry and integral affine structures in non-archimedean mirror symmetry"
DESCRIPTION:Abstract: The SYZ conjecture is a conjectural geometric explanation of mirror symmetry. Based on this\, Kontsevich and Soibelman proposed a non-archimedean approach to mirror symmetry. This led to the notion of essential skeleton and the construction of non-archimedean SYZ fibrations by Nicaise-Xu-Yu. \nIn this talk\, I will introduce these objects and report on recent results extending the approach of Nicaise-Xu-Yu. This yields new types of non-archimedean retractions. For families of quartic K3 surfaces and quintic 3-folds\, the new retractions relate nicely with the results on the dual complex of toric degenerations and on the Gromov-Hausdorff limit of the family. \nThis is based on a work in progress with Léonard Pille-Schneider.  \n  \n[ L’exposé aura lieu en ligne\, sur Zoom. Pour recevoir le lien de connection\, contacter l’organisateur LP] \nVidéo et slides de l’exposé.
URL:https://lmv.math.cnrs.fr/evenenement/ag-enrica-mazzon-mpim-bonn/
CATEGORIES:Séminaire AG
END:VEVENT
BEGIN:VEVENT
DTSTART;VALUE=DATE:20210330
DTEND;VALUE=DATE:20210331
DTSTAMP:20260406T030004
CREATED:20210201T163545Z
LAST-MODIFIED:20210401T142340Z
UID:8943-1617062400-1617148799@lmv.math.cnrs.fr
SUMMARY:Journée du séminaire différentiel
DESCRIPTION:Orateurs : \n\nJason Bell (University of Waterloo\, Ontario\, Canada)\,\nDuco van Straten (Johannes Gutenberg-Universität Mainz\, Mayence\, Allemagne)\,\nMasha Vlasenko (Institute of Mathematics of the Polish Academy of Sciences\, Varsovie\, Pologne).\n\n  \nPlus d’informations à suivre sur la page web du séminaire.
URL:https://lmv.math.cnrs.fr/evenenement/journee-du-seminaire-differentiell/
CATEGORIES:Séminaire AG,Séminaire différentiel
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