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DTSTART;TZID=Europe/Paris:20260106T133000
DTEND;TZID=Europe/Paris:20260106T143000
DTSTAMP:20260620T050337
CREATED:20260102T080023Z
LAST-MODIFIED:20260105T091355Z
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SUMMARY:AG : Manh Linh Nguyen (Jussieu) : Patching and the nine-term Mayer–Vietoris sequence for complexes of tori.
DESCRIPTION:We present the patching method\, a machinery developed by Harbater–Hartmann–Krashen and various other authors\, dedicated to the study of arithmetic of linear algebraic groups over function fields of curves over complete discretely valued fields such as ℚₚ(T). Then\, we present a new result in this direction\, which gives a 9-term exact sequence for Galois cohomology of 2-term complexes of tori in the patching setting. This relies on the notion of (co-)flasque resolutions of such complexes\, generalizing the previous work by Colliot-Thélène–Sansuc. As applications\, we show that patching holds for nonabelian second Galois cohomology of reductive groups with a smooth center\, as well as a weak local–global principle for this cohomology\nset. We also rediscover a local–global principle for indices of central simple algebras.
URL:https://lmv.math.cnrs.fr/evenenement/ag-manh-linh-nguyen-jussieu-patching-and-the-nine-term-mayer-vietoris-sequence-for-complexes-of-tori/
CATEGORIES:Séminaire AG
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DTSTART;TZID=Europe/Paris:20260109T100000
DTEND;TZID=Europe/Paris:20260109T110000
DTSTAMP:20260620T050337
CREATED:20250818T122054Z
LAST-MODIFIED:20260105T222038Z
UID:14295-1767952800-1767956400@lmv.math.cnrs.fr
SUMMARY:PS : Badr-Eddine Cherief Abdellatif (LPSM\, Sorbonne Université) : On Bayesianism and Predictive Uncertainty: Predictively Oriented (PrO) Posteriors
DESCRIPTION:In this talk\, we will present a new statistical principle that combines the most desirable aspects of both parameter inference and density estimation. This leads us to the PrO posterior\, which expresses uncertainty as a consequence of predictive ability. Doing so leads to inferences which predictively dominate both classical and generalised Bayes posterior predictive distributions. Our PrO posteriors adapt to the level of model misspecification: they concentrate around the true model in the same way as Bayes and Gibbs posteriors if the model can recover the data-generating distribution\, but do not concentrate toward a single parameter in the presence of non-trivial forms of model misspecification. Instead\, they stabilise towards a predictively optimal posterior whose degree of irreducible uncertainty admits an interpretation as the degree of model misspecification—a sharp contrast to how Bayesian uncertainty and its existing extensions behave.
URL:https://lmv.math.cnrs.fr/evenenement/ps-badr-eddine-cherief-abdellatif-lpsm-sorbonne-universite/
LOCATION:Bâtiment Fermat\, salle 4205
CATEGORIES:Séminaire PS
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BEGIN:VEVENT
DTSTART;TZID=Europe/Paris:20260109T111500
DTEND;TZID=Europe/Paris:20260109T121500
DTSTAMP:20260620T050337
CREATED:20250818T122423Z
LAST-MODIFIED:20260106T101333Z
UID:14297-1767957300-1767960900@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-steffen-grunewalder-university-of-york/
LOCATION:Bâtiment Fermat\, salle 4205
CATEGORIES:Séminaire PS
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DTSTART;TZID=Europe/Paris:20260127T160000
DTEND;TZID=Europe/Paris:20260127T170000
DTSTAMP:20260620T050337
CREATED:20260123T131000Z
LAST-MODIFIED:20260123T131639Z
UID:14731-1769529600-1769533200@lmv.math.cnrs.fr
SUMMARY:Séminaire des jeunes : Mathieu Da Silva (LMO) : Sur le nombre de valeurs d'une forme binaire irréductible de degré 2 qui s'écrivent comme une norme dans certains corps de nombres abéliens
DESCRIPTION:Résumé : Dans les années 90\, Serre a initié un programme de recherche autour de la probabilité qu’une équation choisie aléatoirement au sein d’une famille possède une solution rationnelle. Par exemple\, il démontra que 0% des coniques diagonales possèdent un point rationnel. Très peu de familles ont été étudiées à ce jour\, bien qu’une conjecture due à Loughran–Smeets prédise un équivalent asymptotique dans certains cas. Dans l’esprit de cette conjecture\, je vais expliquer comment\, étant donné $F \in \Z[s\,t]$ un polynôme homogène irréductible de degré 2 et $L/ \Q$ un corps de nombre abélien dont l’anneau des entiers est principal\, on peut estimer (en ordre de grandeur) la proportion de F(s\,t) qui s’écrivent comme la norme d’un élément de L. La méthode utilisée repose sur des techniques de théorie analytique des nombres comme le crible et la formule de Perron\, ainsi que sur de la géométrie des nombres. \n—\nAbstract: In the 90s\, Serre initiated a research program around the probability that an equation randomly chosen within a family has a rational solution. For example\, he proved that 0% of diagonal conics have a rational point. Very few families have been studied to date\, although a conjecture due to Loughran–Smeets predicts an asymptotic formula in some cases. In the spirit of this conjecture\, I will explain how\, given $F \in \Z[s\,t]$ an irreducible homogeneous polynomial of degree 2 and $L/ \Q$ an abelian number field whose ring of integers is a PID\, we can estimate (in order of magnitude) the proportion of F(s\,t) that are written as the norm of an element of L. The method used is based on techniques from analytic number theory such as the sieve and Perron’s formula\, as well as on geometry of numbers.
URL:https://lmv.math.cnrs.fr/evenenement/seminaire-des-jeunes-mathieu-da-silva-lmo-sur-le-nombre-de-valeurs-dune-forme-binaire-irreductible-de-degre-2-qui-secrivent-comme-une-norme-dans-certains-corps-de-nombres-abeliens/
CATEGORIES:Séminaire des jeunes
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