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X-WR-CALNAME:Laboratoire de Mathématiques de Versailles
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X-WR-CALDESC:Évènements pour Laboratoire de Mathématiques de Versailles
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BEGIN:VEVENT
DTSTART;TZID=Europe/Paris:20260306T110000
DTEND;TZID=Europe/Paris:20260306T120000
DTSTAMP:20260407T011756
CREATED:20260210T224800Z
LAST-MODIFIED:20260302T090259Z
UID:14798-1772794800-1772798400@lmv.math.cnrs.fr
SUMMARY:CRYPTO - Pierrick Dartois - A tale of groups and rabbits: efficient 4-dimensional isogeny computations for cryptographic group actions
DESCRIPTION:A tale of groups and rabbits: efficient 4-dimensional isogeny computations for cryptographic group actions \nIn the transition to post-quantum cryptography\, cryptographic group actions can offer a modularity close to pre-quantum discrete logarithm problems. Not only can this modularity be used for basic primitives (e.g. key exchange\, signatures)\, but also for advanced constructions\, including threshold schemes for secure multi-party computation that will be proposed to the next NIST call. \nIn this talk\, we present how such cryptographic group actions can be instantiated and computed with supersingular isogenies. With standard isogeny computation techniques\, it was only possible to efficiently compute the action of some particular group elements generating the whole group. This limitation could restrict some cryptographic applications where random group elements were used. The (qt-)Pegasis algorithm (Practical Effective class Group Action uSIng 4-dimensional isogenieS) has been introduced last year to overcome this limitation. Following a more and more popular approach in isogeny-based cryptography since the downfall of SIKE (Supersingular Isogeny Key Encapsulation)\, (qt-)Pegasis relies on the computation of a 4-dimensional isogeny. \nThe (qt-)Pegasis algorithm also motivated further research on the efficient computation of 4-dimensional isogenies in order to make it practical and provide an efficient C implementation. We shall conclude the talk with a presentation of recent improvements of 4-dimensional isogeny computation algorithms involving mysterious rabbit-shaped graphs. »
URL:https://lmv.math.cnrs.fr/evenenement/crypto-pierrick-dartois/
LOCATION:Bâtiment Fermat\, salle 4205
CATEGORIES:Séminaire CRYPTO
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Europe/Paris:20260310T160000
DTEND;TZID=Europe/Paris:20260310T170000
DTSTAMP:20260407T011756
CREATED:20260309T133637Z
LAST-MODIFIED:20260313T083002Z
UID:14851-1773158400-1773162000@lmv.math.cnrs.fr
SUMMARY:Séminaire des jeunes : Leonardine Constant - Moduli spaces of curves and stable graphs
DESCRIPTION:In this talk\, I will describe the moduli spaces of curves as a set and present a few key examples. I will also introduce the stable graphs associated to nodal curves.
URL:https://lmv.math.cnrs.fr/evenenement/seminaire-des-jeunes-leonardine-constant-moduli-spaces-of-curves-and-stable-graphs/
CATEGORIES:Séminaire des jeunes
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Europe/Paris:20260312T100000
DTEND;TZID=Europe/Paris:20260312T110000
DTSTAMP:20260407T011756
CREATED:20260210T224623Z
LAST-MODIFIED:20260313T083009Z
UID:14794-1773309600-1773313200@lmv.math.cnrs.fr
SUMMARY:CRYPTO : Paola de Perthuis (CWI) - Predicting Module-Lattice Reduction
DESCRIPTION:Is module-lattice reduction better than unstructured lattice reduction\nThis question was highlighted `Q8′ in the Kyber NIST standardization submission (Avanzi et al.\, 2021)\, as potentially affecting the concrete security of Kyber and other module-lattice based schemes. Foundational works on module-lattice reduction (Lee\, Pellet-Mary\, Stehlé\, and Wallet\, ASIACRYPT 2019; Mukherjee and Stephens-Davidowitz\, CRYPTO 2020) confirmed the existence of such modulevariants of LLL and block-reduction algorithms\, but focus only on provable worst-case asymptotic behavior.\nIn this work\, we present a concrete average-case analysis of module-lattice reduction. Specifically\, we address the question of the expected slope after running module-BKZ\, and pinpoint the discriminant \(\Delta_K\) of the number field at hand as the main quantity driving this slope. We convert this back into a gain or loss on the blocksize \(\beta\): module-BKZ in a number field \(K\) of degree \(d\) requires an SVP oracle of dimension \(\beta + \log(|\Delta_K| / d^d)\beta /(d\log \beta) + o(\beta / \log \beta)\) to reach the same slope as unstructured BKZ with blocksize \(\beta\). This asymptotic summary hides further terms that we predict concretely using experimentally verified heuristics. Incidentally\, we provide the first open-source implementation of module-BKZ for some cyclotomic fields.\nFor power-of-two cyclotomic fields\, we have \(|\Delta_K| = d^d\)\, and conclude that module-BKZ requires a blocksize larger than its unstructured counterpart by \(d-1+o(1)\). On the contrary\, for all other cyclotomic fields we have \(|\Delta_K| < d^d\)\, so module-BKZ provides a sublinear \(\Theta(\beta/\log \beta)\) gain on the required blocksize\, yielding a subexponential speedup of \(\exp(\Theta(\beta/\log \beta))\) \nhttps://eprint.iacr.org/2025/1904
URL:https://lmv.math.cnrs.fr/evenenement/crypto-paola-de-perthuis/
LOCATION:Bâtiment Fermat\, salle 4205
CATEGORIES:Séminaire CRYPTO
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Europe/Paris:20260317T133000
DTEND;TZID=Europe/Paris:20260317T143000
DTSTAMP:20260407T011756
CREATED:20260121T212551Z
LAST-MODIFIED:20260319T110212Z
UID:14722-1773754200-1773757800@lmv.math.cnrs.fr
SUMMARY:AG : Trung Nghiem : Université Lyon 1 : Une construction effective des variétés de Calabi–Yau asymptotiquement coniques
DESCRIPTION:Une métrique asymptotiquement conique de Calabi–Yau est une métrique kählérienne à courbure de Ricci nulle\, dont l’allure à l’infini ressemble à un cône de Calabi–Yau. Un travail récent de Conlon–Hein montre qu’une variété AC de Calabi–Yau à cône asymptotique donné est obtenue soit par déformation\, soit par désingularisation crépante du cône. En fonction de la métrique sur le cône\, la variété AC est dite quasi-régulière ou irrégulière. Les exemples du dernier sont notamment rares dans la littérature et relativement beaucoup moins faciles à construire que les exemples quasi-réguliers. Dans mon exposé\, je vais présenter une stratégie effective pour construire des variétés non-compactes de Calabi–Yau irrégulières via la théorie d’Altmann sur les déformations des cônes toriques de Calabi–Yau. Il s’agit d’un travail en commun avec Ronan J. Conlon (University of Texas\, Dallas).
URL:https://lmv.math.cnrs.fr/evenenement/trung-nghiem-universite-lyon-1/
CATEGORIES:Séminaire AG
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Europe/Paris:20260324T133000
DTEND;TZID=Europe/Paris:20260324T143000
DTSTAMP:20260407T011756
CREATED:20260315T174427Z
LAST-MODIFIED:20260327T131156Z
UID:14871-1774359000-1774362600@lmv.math.cnrs.fr
SUMMARY:AG : Lucas Gerth (Jussieu) : Moduli spaces of analytic p-divisible groups.
DESCRIPTION:Abstract: We prove a classification of families of analytic p-divisible groups on adic spaces S over Qp in terms of Hodge–Tate triples on S\, generalizing a theorem of Fargues. From this\, for S a perfectoid space\, we construct an analytic Dieudonné theory with values in mixed characteristic Shtukas over the Fargues–Fontaine disc. As applications\, we realize the local Shimura varieties of EL and PEL type of Scholze–Weinstein as moduli spaces of analytic p-divisible groups with framed universal cover\, and we reinterpret the Hodge–Tate period map of Scholze in terms of topologically p-torsion subgroups of abelian varieties.
URL:https://lmv.math.cnrs.fr/evenenement/ag-lucas-gerth-jussieu/
CATEGORIES:Séminaire AG
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Europe/Paris:20260324T160000
DTEND;TZID=Europe/Paris:20260324T170000
DTSTAMP:20260407T011756
CREATED:20260309T133800Z
LAST-MODIFIED:20260327T131214Z
UID:14853-1774368000-1774371600@lmv.math.cnrs.fr
SUMMARY:Séminaire des jeunes : Nailya Manatova (LMV) : Finite time blow up for the critical generalized KdV equation.
DESCRIPTION:I will present some general results on the finite-time blow-up of the mass critical gKdV equation. Then\, we will focus on results concerning finite-time infinite-point blow-up. Previously\, the blow-up rate of such solutions was limited with a lower bound of 11/13; in my work\, this has been improved to 1/2. The critical blow up rate 1/2\, is in the transition between infinite and finite point blow up. This year I’ve constructed solutions in the related regime\, which is close to my previous work and presents some form of stability. Recently\, in the work of Y.Martel and D. Pilod\, the interval of finite point blow up rates was also improved\, we will introduce these results.
URL:https://lmv.math.cnrs.fr/evenenement/seminaire-des-jeunes-3/
LOCATION:Bâtiment Fermat\, salle 4205
CATEGORIES:Séminaire des jeunes
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Europe/Paris:20260326T140000
DTEND;TZID=Europe/Paris:20260326T150000
DTSTAMP:20260407T011756
CREATED:20260113T122300Z
LAST-MODIFIED:20260327T131224Z
UID:14705-1774533600-1774537200@lmv.math.cnrs.fr
SUMMARY:EDP : Lucie Baudouin (LAAS & CNRS\, Toulouse) : From Stability to Reconstruction: Carleman-Based Algorithms for Wave Equation Coefficients
DESCRIPTION:This talk focuses on the reconstruction of unknown coefficients in the wave equation\, leveraging the power of Carleman inequalities. We aim at designing a global reconstruction algorithm for coefficients – such as time-independent potentials or wave propagation speeds – from Neumann boundary measurements of the solution. We begin by revisiting the historical foundations of uniqueness and stability results for this inverse problem\, established over 25 years ago using local and global Carleman estimates. Building on these insights\, we present a more recently developed reconstruction algorithm that exploits the same technical tools to ensure global convergence\, avoiding possible local minima encountered by conventional methods. The algorithm is grounded in the minimization of a functional derived from the Carleman weight function\, directly inspired by the stability proof strategy. The talk will outline the key steps in proving the algorithm’s convergence for reconstructing coefficients in bounded domains or networks. These works are the result of various long-standing collaborations with Maya de Buhan\, Emmanuelle Crépeau\, Sylvain Ervedoza\, Axel Osses\, and Julie Valein.
URL:https://lmv.math.cnrs.fr/evenenement/edp-lucie-baudouin-laas-cnrs-toulouse/
LOCATION:Bâtiment Fermat\, salle 4205
CATEGORIES:Séminaire EDP
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Europe/Paris:20260326T153000
DTEND;TZID=Europe/Paris:20260326T163000
DTSTAMP:20260407T011756
CREATED:20260305T191859Z
LAST-MODIFIED:20260327T131235Z
UID:14836-1774539000-1774542600@lmv.math.cnrs.fr
SUMMARY:EDP : Luc Robbiano (LMV) : Stabilisation des équations des ondes avec un amortissement interne retardé
DESCRIPTION:On présentera le modèle et on donnera des exemples où le retard déstabilise complètement le système même pour des petits retards.\nOn donnera aussi des résultats de stabilisation exponentielle sous une condition analogue à la condition de contrôle géométrique dans le contexte des variétés sans bord. Ce résultat repose sur une étude pour sur les petites fréquences\, dans ce cas on supposera le retard petit et une étude à hautes fréquences.
URL:https://lmv.math.cnrs.fr/evenenement/edp-luc-robbiano-lmv/
LOCATION:Bâtiment Fermat\, salle 4205
CATEGORIES:Séminaire EDP
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Europe/Paris:20260327T100000
DTEND;TZID=Europe/Paris:20260327T110000
DTSTAMP:20260407T011756
CREATED:20250922T131835Z
LAST-MODIFIED:20260327T131258Z
UID:14351-1774605600-1774609200@lmv.math.cnrs.fr
SUMMARY:PS : Steffen Grünewälder (University of York) : Mesure Empirique Compressée
DESCRIPTION:Je présenterai une approche visant à compresser la mesure empirique tout en préservant les vitesses de convergence dans le contexte des méthodes à noyau. Je donnerai d’abord une vue d’ensemble de l’idée\, avant de démontrer deux résultats clés.
URL:https://lmv.math.cnrs.fr/evenenement/ps-manon-costa-institut-de-mathematiques-de-toulouse/
LOCATION:Bâtiment Fermat\, salle 4205
CATEGORIES:Séminaire PS
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Europe/Paris:20260327T111500
DTEND;TZID=Europe/Paris:20260327T121500
DTSTAMP:20260407T011756
CREATED:20250922T132030Z
LAST-MODIFIED:20260327T131306Z
UID:14353-1774610100-1774613700@lmv.math.cnrs.fr
SUMMARY:PS : Davide Giraudo (IRMA\, Strasbourg) : Détection de rupture dans un échantillon de loi de type Pareto via une U-statistique
DESCRIPTION:On cherche à déterminer si les observations d’un échantillon sont issues de réalisations de variables aléatoires de même loi de type Pareto\, c’est-à-dire dont la queue se comporte comme une puissance négative fois une fonction à variations lentes. Pour cela\, nous proposons un test basé sur une U-statistique construite en divisant l’échantillon en blocs de même taille et à regarder la différence moyenne entre les estimateurs de Hill basés sur des paires de blocs. Nous fournirons les garanties théoriques ainsi que pratiques de ce test. Il s’agit d’un travail réalisé en collaboration avec Armelle Guillou\, disponible ici  https://hal.science/IRMASTAT/hal-05424414v1.
URL:https://lmv.math.cnrs.fr/evenenement/ps-davide-giraudo-irma-strasbourg/
LOCATION:Bâtiment Fermat\, salle 4205
CATEGORIES:Séminaire PS
END:VEVENT
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