For a Shimura variety of Hodge type with hyperspecial level at a prime $p$, the Newton stratification on its special fiber at $p$ is a stratification defined in terms of the isomorphism class of the Dieudonne module of parameterized abelian varieties endowed with a certain fixed set of Frobenius-invariant crystalline cycles ("$F$-isocrystal with $G_{\mathbb{Q}_p}$-structure"). There has been a conjectural group-theoretic description of the F-isocrystals that are expected to show up in the special fiber. We confirm this conjecture by two different methods. More precisely, for any $F$-isocrystal with $G_{\mathbb{Q}_p}$-structure that is expected to appear (in a precise sense), first we construct a special point which has good reduction and whose reduction has associated $F$-isocrystal equal to given one. Secondly, we produce a Kottwtiz triple (with trivial Kottwitz invariant) with the $F$-isocrystal component being the given one. According to a recent result of Kisin which establishes the Langlands-Rapoport conjecture, such Kottwitz triple arises from a point in the reduction.
In this paper we study the geometry of reduction modulo $p$ of the Kisin-Pappas integral models for certain Shimura varieties of abelian type with parahoric level structure. We give some direct and geometric constructions for the EKOR strata on these Shimura varieties, using the theories of $G$-zips and mixed characteristic local $\mathcal{G}$-Shtukas. We establish several basic properties of these strata, including the smoothness, dimension formula, and closure relation. Moreover, we apply our results to the study of Newton strata and central leaves on these Shimura varieties.
We prove vanishing results for the $0$th cohomology of automorphic line bundles on the Ekedahl--Oort strata of the special fiber of Hilbert--Blumenthal Shimura varieties. This work vastly extends to all Ekedahl--Oort strata previous results of Diamond--Kassaei and Goldring--Koskivirta. Furthermore, our results also cover the case of unitary Shimura varieties of rank $\leq 2$ attached to an arbitrary CM extension. We also prove a conjecture of Goldring--Koskivirta on the set of possible weights of automorphic forms.
Let $S$ be the special fibre of a Shimura variety of Hodge type, with good reduction at a place above $p$. We give an alternative construction of the zip period map for $S$, which is used to define the Ekedahl-Oort strata of $S$. The method employed is local, $p$-adic, and group-theoretic in nature.
The Hecke orbit conjecture asserts that every prime-to-$p$ Hecke orbit in a Shimura variety is dense in the central leaf containing it. In this paper, we prove the conjecture for certain irreducible components of Newton strata in Shimura varieties of PEL type A and C, when $p$ is an unramified prime of good reduction. Our approach generalizes Chai and Oort's method for Siegel modular varieties.
Ekedahl-Oort strata with a superspecial factor in unitary Shimura varieties
Washington College（华盛顿学院）；Carleton College（卡尔顿学院）；Brooklyn College and The Graduate Center, City University of New York（纽约市立大学布鲁克林学院及研究生院）；Korteweg-de Vries Institute for Mathematics, University of Amsterdam（阿姆斯特丹大学科特维格-德弗里斯数学研究所）；University of Arizona（亚利桑那大学）
On the classification of indecomposable Ekedahl-Oort strata in unitary Shimura varieties, and related Newton polygons
Washington College（华盛顿学院）；Carleton College（卡尔顿学院）；Oklahoma State University（俄克拉荷马州立大学）；Brooklyn College, City University of New York（纽约市立大学布鲁克林学院）；Korteweg-de Vries Institute for Mathematics, University of Amsterdam（阿姆斯特丹大学科特维格-德弗里斯数学研究所）；Colorado State University（科罗拉多州立大学）
Admissible morphisms for Shimura varieties with parahoric levels
在\textit{Shimuravarietäten und Gerben} \cite{LR87}中，Langlands和Rapoport发展了伪运动伽罗瓦格伯和伽罗瓦格伯之间的容许态射理论，以期对Shimura簇的超特殊水平的好约化的$\bar{\mathbb{F}}_p$ -点集进行系统描述，并为其解析提供潜在的工具。在这里，我们推广，并在一定程度上提高，他们的工作时，集团是准分裂在$p$的parahoric水平。特别地，我们证明了每一个容许态射都共轭于一个特殊的容许态射，并且当其水平是特殊的极大仿射时，任何具有平凡Kottwitz不变量的Kottwitz三元组，如果它满足猜想所隐含的一些明显的必要条件，则来自一个容许对.作为应用，我们给出了容许对和Kottwitz三元组的自然有效性准则，并在相应的情形下建立了Newton层的非空性。一路上，我们填补了原始工作中的一些空白。
Let $\mathcal{A}_{g}$ be the moduli space of $g$-dimensional principally polarized abelian varieties over $\mathbb{Z}$, and let $\mathcal{T} \subset \mathcal{A}_{g}$ be a closed locus, also defined over $\mathbb{Z}$. Motivated by unlikely intersection conjectures, we study the intersection of $\mathcal{T}_{\mathbb{F}_{p}}$ with the Bruhat strata in $\mathcal{A}_{g,\mathbb{F}_{p}}$ as $p$-varies; these are strata characterized by the existence of certain subgroup schemes inside the $p$-torsion of the fibres. We find that, away from a finite set of primes, positive-dimensional ``unlikely'' inter…
In this paper we study the geometry of the special fiber of Pappas-Rapoport models of Shimura varieties in the Hilbert case. More precisely we prove that the stratification induced by the Hodge polygon is a good stratification, which is false in the Hilbert-Siegel case for $g\geq 2$. Then we use known results on the convolution product of affine Grassmannians to describe the dimension of the strata and obtain that the forgetting morphism to the Kottwitz PEL model is flat in restriction to Hodge strata.
In this article we compute the mass associated to any unimodular lattice in a Hermitian space over an arbitrary CM field under a condition at 2. We study the geometry and arithmetic of the basic locus of the GU(r,s)-Shimura variety associated to an imaginary quadratic field modulo a good prime p>2. We give explicit formulas for the numbers of irreducible and connected components of the basic locus, and of points of the zero-dimensional Ekedahl-Oort (EO) stratum, as well as of the irreducible components of basic EO strata when the signature is either (1, n-1) or (2,2).
