Séminaire de l’équipe TA
Responsables : AUSONI Christian et DE CLERCQ Charles
Jeudi 5 novembre 2026
14:00 Tasos MOULINOS (Université de Paris-Saclay)
Résumé
Height one phenomena in p-adic Hodge theory
Salle B405, bâtiment B, LAGA, Institut Galilée, Université Paris 13The syntomification of the integers (Z_p^syn) acts as a parameter space for p-adic cohomology theories. By the work of Drinfeld and others, it is known to carry a canonical formal group, and hence a map to the moduli stack of formal groups. Pulling back along this map gives rise to a certain line bundle equipped with a distinguished section "v_1". On the p-completed moduli stack of formal groups, the nonvanishing of v_1 defines the substack parametrizing "height-1" formal groups. Yet the preimage of this locus on Z_p^syn, when computed in p-adic formal stacks, is empty. There is a mismatch here because inverting v_1 on syntomic cohomology gives p-adic étale cohomology, but inverting it on the stack itself before passing to global sections gives nothing.
I will explain how passing to analytic stacks brings this missing locus into view. By realizing the p-completed moduli stack of formal groups as an analytic stack, we construct an algebro-geometric shadow of K(1)-localization. Applied to syntomification, this produces an analytic stack whose dualizable quasi-coherent sheaves recover p-adic Galois representations, and more generally lisse étale sheaves on the generic fiber of a p-adic formal scheme. I will explain how a perfected version of this construction depends only on the generic fiber, providing a geometric counterpart to purity results for K(1)-localized K-theory.
This is joint work in progress with Greg Andreychev.
Vendredi 6 novembre 2026
10:30 Adam MORGAN (Gonville and Caius College, Cambridge)
Résumé
On the Hasse principle in twist families
Séminaire commun AGA/TA
Salle B407, bâtiment B, LAGA, Institut Galilée, Université Paris 13I will discuss joint work with Alex Bartel in which we study the frequency of failures of the Hasse principle in quadratic twist families of torsors under an abelian variety. The main technical ingredient is a result on the distribution of 2-Selmer groups in certain families of twists defined by Frobenian conditions.
Jeudi 12 novembre 2026
14:00 Pierre BODIN (LAGA, Université Sorbonne Paris Nord)
Résumé
Minimal model for localization of topological Fukaya categories of surfaces
Salle B405, bâtiment B, LAGA, Institut Galilée, Université Paris 13In the first half of this talk, I will present the construction of the topological Fukaya category of a graded marked surface, as introduced by Haiden, Katzarkov, Kontsevich, and present some of its main properties.
In the second half, I will present a minimal model for the localization of this category at a spherical object corresponding to a simple closed curve on the surface. This new description will then be used to describe the indecomposable objects of the localization in terms of graded curves on the singular surface obtained by collapsing the simple closed curve to a point.