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We develop the basic theory of derived quasi-coherent ideals for stacks relative to a given derived algebraic context. We compare different notions of adic completeness with respect to derived ideals, define and compare formal spectra and…

Algebraic Geometry · Mathematics 2025-11-26 Zachary Gardner , Jeroen Hekking

Let $V$ be a linear representation of a connected complex reductive group $G$. Given a choice of character $\theta$ of $G$, Geometric Invariant Theory defines a locus $V^{ss}_\theta(G) \subseteq V$ of semistable points. We give necessary,…

Representation Theory · Mathematics 2025-10-07 Riku Kurama , Ruoxi Li , Henry Talbott , Rachel Webb

We give a criterion under which one can obtain a good decomposition (in the sense of Malgrange) of a formal flat connection on a complex analytic or algebraic variety of arbitrary dimension. The criterion is stated in terms of the spectral…

Algebraic Geometry · Mathematics 2019-12-19 Kiran S. Kedlaya

Given a formal flat meromorphic connection over an excellent scheme over a field of characteristic zero, in a previous paper we established existence of good formal structures and a good Deligne-Malgrange lattice after suitably blowing up.…

Algebraic Geometry · Mathematics 2019-03-11 Kiran S. Kedlaya

We prove a direct image theorem stating that the direct image of a Galois formula by a morphism of difference schemes is equivalent to a Galois formula over fields with powers of Frobenius. As a consequence, we obtain an effective…

Algebraic Geometry · Mathematics 2012-10-16 Ivan Tomasic

We obtain algebraic Frobenius manifolds from classical $W$-algebras associated to subregular nilpotent elements in simple Lie algebras of type $D_r$ where $r$ is even and $E_r$. The resulting Frobenius manifolds are certain hypersurfaces in…

Differential Geometry · Mathematics 2011-08-30 Yassir Dinar

We set up the geometric background necessary to extend rigid cohomology from the case of algebraic varieties to the case of general locally noetherian formal schemes. In particular, we generalize Berthelot's strong fibration theorem to adic…

Algebraic Geometry · Mathematics 2022-09-19 Bernard Le Stum

We apply methods of derived and non-commutative algebraic geometry to understand ramification phenomena on arithmetic schemes. As an application, we prove the Deligne-Milnor conjecture and, in the pure characteristic case, a generalization…

Algebraic Geometry · Mathematics 2024-10-04 Dario Beraldo , Massimo Pippi

This paper is about sheaf cohomology for varieties (schemes) in characteristic $p>0$. We assume the presence of a Frobenius splitting. (See V.B. Mehta and A. Ramanathan, Frobenius splitting and cohomology vanishing for Schubert varieties,…

alg-geom · Mathematics 2009-10-22 V. B. Mehta , Wilberd van der Kallen

When the quantum parameter $q^{\frac{1}{2}}$ is a root of unity of odd order and the punctured bordered surface has nonempty boundary, we prove the fraction ring of the stated skein algebra (that is the localization over all nonzero…

Geometric Topology · Mathematics 2023-10-23 Zhihao Wang

Let $X/\mathbb{C}$ be a smooth variety with simple normal crossings compactification $\bar{X}$, and let $L$ be an irreducible $\overline{\mathbb{Q}}_{\ell}$-local system on $X$ with torsion determinant. Suppose $L$ is cohomologically rigid.…

Algebraic Geometry · Mathematics 2023-12-05 Raju Krishnamoorthy , Yeuk Hay Joshua Lam

We generalise a theorem on the existence of Frobenius isocrystal and Fontaine-Laffaille module structures on rigid flat connections to the non-proper setting. The proof is based on a new strategy of a point-set topological flavour, which…

Algebraic Geometry · Mathematics 2023-11-23 Hélène Esnault , Michael Groechenig

We study foliations of space forms by complete hypersurfaces, under some mild conditions on its higher order mean curvatures. In particular, in Euclidean space we obtain a Bernstein-type theorem for graphs whose mean and scalar curvature do…

Differential Geometry · Mathematics 2009-08-07 A. Caminha , P. Sousa , F. Camargo

We introduce a notion of proper morphism for schematic finite spaces and prove the analogue of Grothendieck's finiteness theorem for it by means of the classic result for schemes and general descent arguments. This result also generalizes…

Algebraic Geometry · Mathematics 2023-05-22 Javier Sánchez González

Cases of Deligne's companion conjecture for normal schemes over finite fields have been proven by L. Lafforgue, Drinfeld, and Zheng in recent years: L. Lafforgue proved the conjecture for curves, Drinfeld proved the conjecture for all…

Number Theory · Mathematics 2026-01-09 Min Shi

Let X be a complex algebraic variety, and L(X) be the scheme of formal arcs in X. Let f be an arc whose image is not contained in the singularities of X. We show that the formal neighborhood of f in L(X) admits a decomposition into a…

Algebraic Geometry · Mathematics 2007-05-23 Mikhail Grinberg , David Kazhdan

In this follow-up paper we show that smooth Hodge-proper stacks over $\mathcal O_K$ are $\mathbb Q_p$-locally acyclic: namely the natural map between \'etale $\mathbb Q_p$-cohomology of the algebraic and Raynaud generic fibers is an…

Algebraic Geometry · Mathematics 2022-12-01 Haoyang Guo , Dmitry Kubrak , Artem Prikhodko

Given a spectral Deligne-Mumford stack $X$, we define a perception of $X$ to be a collection of a certain class of morphisms $Y \rightarrow X$. For the class of affine morphisms in SpDM, we show that from QCoh($X$) on can extract the affine…

Algebraic Geometry · Mathematics 2021-06-17 Renaud Gauthier

In this paper we describe several new aspects of the foundations of the representation theory of the space of smooth-automorphic forms (i.e., not necessarily $K_\infty$-finite automorphic forms) for general connected reductive groups over…

Number Theory · Mathematics 2021-08-17 Harald Grobner , Sonja Žunar

We prove the equidimensionality of affine Deligne-Lusztig varieties in mixed characteristic. This verifies a conjecture made by Rapoport and implies that the results of Nie and Zhou-Zhu can be extended to the whole irreducible components of…

Algebraic Geometry · Mathematics 2025-08-14 Yuta Takaya