Thomas J. Haines
This survey article explains the construction of Rapoport-Zink local models and their use in understanding various questions relating to the singularities in the reduction modulo p of certain Shimura varieties with parahoric level structure at p.
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We investigate the geometry of the special fiber of the integral model of a Shimura variety with parahoric level at a given prime place. To be more precise, we deal with the definition of central leaves in this situation, their local closedness, and the relationship between the folations for varying parahoric level. This is connected to the verification of axioms for integral models formulated by He and Rapoport.
Integral models of Shimura varieties with parahoric level structure, II
本文构造了具有paraoric层级结构的Abelian型Shimura变种的整数模型，这些模型在étale局部上与相应的局部模型同构。
We investigate the geometry of the special fiber of the integral model of a Shimura variety with parahoric level at a given prime place. To be more precise, we deal with the EKOR stratification which interpolates between the Ekedahl-Oort and Kottwitz-Rapoport stratifications. In the Siegel case we give a geometric description by suitably generalizing the theory of $G$-zips of Moonen, Wedhorn, Pink and Ziegler to our context.
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.
For an odd prime p, we construct integral models over p for Shimura varieties with parahoric level structure, attached to Shimura data (G,X) of abelian type, such that G splits over a tamely ramified extension of Q_p. The local structure of these integral models is related to certain "local models", which are defined group theoretically. Under some additional assumptions, we show that these integral models satisfy a conjecture of Kottwitz which gives an explicit description for the trace of Frobenius action on their sheaf of nearby cycles.
Regular models of ramified unitary Shimura varieties at maximal parahoric level
本文利用分裂模型的思想，定义并研究了在分歧素数处具有极大抛物水平结构的符号为$(n-1,1)$的酉Shimura簇的半稳定模型，证明了该情形下的真正分裂模型是平坦且具有半稳定约化的。
In this paper, we study the basic locus in the fiber at $p$ of a certain unitary Shimura variety with a certain parahoric level structure. The basic locus $\widehat{\mathcal{M}^{ss}}$ is uniformized by a formal scheme $\mathcal{N}$ which is called Rapoport-Zink space. We show that the irreducible components of the induced reduced subscheme $\mathcal{N}_{red}$ of $\mathcal{N}$ are Deligne-Lusztig varieties and their intersection behavior is controlled by a certain Bruhat-Tits building. Also, we define special cycles in $\mathcal{N}$ and study their intersection multiplicities.
In this paper, we formulate conjectural formulas for the arithmetic intersection numbers of special cycles on unitary Shimura varieties with minuscule parahoric level structure. Also, we prove that these conjectures are compatible with all known results.
$2$-adic integral models of some Shimura varieties with parahoric level structure
本文在 $p=2$ 上为具有抛物层结构的阿贝尔型 Shimura 簇构造整模型，并证明 Hodge 型情形下这些模型在 Pappas-Rapoport 意义下是典范的。
Kisin and Pappas constructed integral models of Hodge-type Shimura varieties with parahoric level structure at $p>2$, such that the formal neighbourhood of a mod~$p$ point can be interpreted as a deformation space of $p$-divisible group with some Tate cycles (generalising Faltings' construction). In this paper, we study the central leaf and the closed Newton stratum in the formal neighbourhoods of mod~$p$ points of Kisin-Pappas integral models with parahoric level structure; namely, we obtain the dimension of central leaves and the almost product structure of Newton strata. In the case of hype…
In \textit{Shimuravarietäten und Gerben} \cite{LR87}, Langlands and Rapoport developed the theory of pseudo-motivic Galois gerb and admissible morphisms between Galois gerbs, with a view to formulating a conjectural description of the $\bar{\mathbb{F}}_p$-point set of the good reduction of a Shimura variety with hyperspecial level, as well as to providing potential tools for its resolution. Here, we generalize, and also improve to some extent, their works to parahoric levels when the group is quasi-split at $p$. In particular, we show that every admissible morphism is conjugate to a special ad…
On the Kudla-Rapoport conjecture for unitary Shimura varieties with maximal parahoric level structure at unramified primes
本文通过 Deligne-Lusztig 簇的 Tate 猜想版本证明 Kudla-Rapoport 猜想，并在任意维数的若干新情形下无条件成立。
Mod $p$ points on Shimura varieties of parahoric level (with an appendix by Rong Zhou)
本文研究 parahoric 层 Hodge 型 Shimura 簇积分模型的模 $p$ 点，通过归约到非常特殊 parahoric 情形证明 CM 点约化猜想及 Langlands–Rapoport 预测，并确定 Ekedahl–Oort 层连通分支。
Relative representability and parahoric level structures
本文基于$v$-sheaf理论修正的形式方案可表示性准则，研究局部shtukas上的paraoric层次结构模空间，并探讨超专层次下Shimura品种积分模型的局部可表示性及forgetful映射性质。
We show how to characterize integral models of Shimura varieties over places of the reflex field where the level subgroup is parahoric by formulating a definition of a "canonical" integral model. We then prove that in Hodge type cases and under a tameness hypothesis, the integral models constructed by the author and Kisin in previous work are canonical and, in particular, independent of choices. A main tool is a theory of displays with parahoric structure that we develop in this paper.
In this article, we treat two questions on Rapoport--Zink spaces of Hodge type constructed by Hamacher and Kim. One of which is their singularities, and the other is $p$-adic uniformization of Shimura varieties. More precisely, we prove that the singularity of a Rapoport--Zink space is controlled by its asssociated local model, and the basic locus of a Kisin--Pappas integral model of a Shimura variety is uniformized by the corresponding Rapoport--Zink space. These results extend the known facts by Rapoport and Zink in the case of PEL type.
For a prime $p>2$, Kisin and Pappas constructed parahoric integral models at $p$ for Shimura varieties attached to Shimura data $(G,X)$ of abelian type such that $G$ splits over a tamely ramified extension of $\mathbb{Q}_p$. A certain auxiliary data has to be chosen in their constructions. In this note, we will show that the parahoric integral models are actually independent of the choices of the auxiliary data. We also get partial results on extending morphisms of Shimura varieties to those of parahoric integral models.
Motivated by the desire to understand the geometry of the basic loci in the reduction of Shimura varieties, we study their "group-theoretic models" -- generalized affine Deligne-Lusztig varieties -- in cases where they have a particularly nice description. Continuing the work of [GH] and [GHN] we single out the class of cases of Coxeter type, give a characterization in terms of the dimension, and obtain a complete classification. We also discuss known, new and open cases from the point of view of Shimura varieties/Rapoport-Zink spaces.
This is a report on results and methods in the reduction modulo p of Shimura varieties with parahoric level structure. In the first part, the local theory, we explain the concepts of parahoric subgroups, of the mu-admissible and mu-permissible subsets of the Iwahori-Weyl group, of the corresponding union of affine Deligne-Lusztig varieties and of local models. In the second part, the global theory, we use these concepts to formulate conjectures on the points in the reduction modulo p of Shimura varieties with parahoric level structure.
The motivation for this paper is the study of arithmetic properties of Shimura varieties, in particular the Newton stratification of the special fiber of a suitable integral model at a prime with parahoric level structure. This is closely related to the structure of Rapoport-Zink spaces and of affine Deligne-Lusztig varieties. We prove a Hodge-Newton decomposition for affine Deligne-Lusztig varieties and for the special fibres of Rapoport-Zink spaces, relating these spaces to analogous ones defined in terms of Levi subgroups, under a certain condition (Hodge-Newton decomposability) which can b…
Toric schemes and integral models for Shimura varieties with $Γ_1(p)$-type level
本文提出关于具有p-整模型的Shimura品种的猜想理论，基于parahoric子群的正常子群及其abelian商群，结合根堆栈和toric品种理论，证明了在PEL型Shimura品种中Iwahori情况下的猜想。
Regular integral models of Shimura varieties and a conjecture of Pappas
本文为辛型和正交型 Shimura 簇在极大抛物水平构造正则整模型，通过爆破 Schubert 簇实现等变修改，证明了 Pappas 猜想。
p-adic shtukas and the theory of global and local Shimura varieties
本文建立了p-adic shtukas的基本结果，并将其应用于局部与全局Shimura簇理论，为具有parahoric level结构的Hodge型Shimura簇构造了典范整模型。
We prove the test function conjecture of Kottwitz and the first named author for local models of Shimura varieties with parahoric level structure, and their analogues in equal characteristic.
Canonical integral models for Shimura varieties of toral type
本文在环面型 Shimura 簇情形下证明了 Pappas-Rapoport 猜想，并利用棱镜 F-晶体理论建立了 G-值晶体表示与 G-shtuka 之间的全忠实函子。
We study the singularities of integral models of Shimura varieties and moduli stacks of shtukas with parahoric level structure. More generally our results apply to the Pappas-Zhu and Levin mixed characteristic parahoric local models, and to their equal characteristic analogues. For any such local model we prove under minimal assumptions that the entire local model is normal with reduced special fiber and, if $p>2$, it is also Cohen-Macaulay. This proves a conjecture of Pappas and Zhu, and shows that the integral models of Shimura varieties constructed by Kisin and Pappas are Cohen-Macaulay as …
We study the prime-to-$p$ Hecke action on the projective limit of the sets of connected components of Shimura varieties with fixed parahoric or Bruhat--Tits level at $p$. In particular, we construct infinitely many Shimura varieties for CM unitary groups in odd variables for which the considering actions are not transitive. We prove this result by giving negative examples on the question of Bruhat--Colliot-Thélène--Sansuc--Tits or its variant, which is related to the weak approximation on tori over $\mathbb{Q}$.
In this article, we give a concrete description of the underlying reduced subscheme of the Rapoport--Zink spaces for spinor similitude groups with special maximal parahoric (and non-hyperspecial) level structure. Moreover, we give two applications of the above result. One of which is describing the structure of the basic loci of mod $p$ reductions of Kisin--Pappas integral models of Shimura varieties for spinor similitude groups with special maximal parahoric level structure at $p$. The other is constructing a variant of the result of He, Li and Zhu, which gives a formula on the intersection m…
The connected components of affine Deligne--Lusztig varieties
本文通过p-adic Hodge理论方法，全面解决了affine Deligne-Lusztig变种和局部Shimura变种的连通分量问题，并推导了关于Shimura变种积分模型的新几何结果。
We give a group theoretic definition of "local models" as sought after in the theory of Shimura varieties. These are projective schemes over the integers of a $p$-adic local field that are expected to model the singularities of integral models of Shimura varieties with parahoric level structure. Our local models are certain mixed characteristic degenerations of Grassmannian varieties; they are obtained by extending constructions of Beilinson, Drinfeld, Gaitsgory and the second-named author to mixed characteristics and to the case of general (tamely ramified) reductive groups. We study the sing…
In this paper, we study the $μ$-ordinary locus of a Shimura variety with parahoric level structure. Under the axioms in \cite{HR}, we show that $μ$-ordinary locus is a union of some maximal Ekedahl-Kottwitz-Oort-Rapoport strata introduced in \cite{HR} and we give criteria on the density of the $μ$-ordinary locus.
Canonical Integral Models of Shimura Varieties of Abelian Type
本文证明了当 $p>3$ 时，所有具有 parahoric 层结构的阿贝尔型 Shimura 簇的 Kisin-Pappas-Zhou 积分模型是典范的，从而验证了 Pappas-Rapoport 猜想，并表明这些模型独立于构造选择且满足函子性。
On $\mathbb J$-strata with Parahoric Stabilizers in Affine Deligne-Lusztig Varieties
本文通过构造到称为小余特征组合不变量的自然双射，参数化了基本仿射Deligne-Lusztig簇中稳定子为抛物子群的$\mathbb J$-分层，并证明了这些分层的基数等于$\mu$的Weyl群轨道中某个子集的基数。
We continue our study of the reduction of PEL Shimura varieties with parahoric level structure at primes p at which the group that defines the Shimura variety ramifies. We describe "good" $p$-adic integral models of these Shimura varieties and study their 'etale local structure. In this paper we mainly concentrate on the case of unitary groups for a ramified quadratic extension. Some of our results are applications of the theory of twisted affine flag varieties in our previous paper math.AG/0607130.
This paper is a continuation of [G-dS1]. We study foliations of two types on Shimura varieties $S$ in characteristic $p$. The first, which we call "tautological foliations", are defined on Hilbert modular varieties, and lift to characteristic $0$. The second, the "$V$-foliations", are defined on unitary Shimura varieties in characteristic $p$ only, and generalize the foliations studied by us before, when the CM field in question was quadratic imaginary. We determine when these foliations are $p$-closed, and the locus where they are smooth. Where not smooth, we construct a "successive blow up" …
We construct projective toroidal compactifications for integral models of Shimura varieties of Hodge type. We also construct integral models of the minimal (Satake-Baily-Borel) compactification. Our results essentially reduce the problem to understanding the integral models themselves. As such, they cover all previously known cases of PEL type, as well as all cases of Hodge type involving parahoric level structures. At primes where the level is hyperspecial, we show that our compactifications are canonical in a precise sense. We also provide a new proof of Y. Morita's conjecture on the everywh…
Consider a PEL-Shimura variety associated to a unitary group that splits over an unramified extension of Q_p. Rapoport and Zink have defined a model of the Shimura variety over the ring of integers of the completion of the reflex field at a place lying over p, with parahoric level structures at p. We show that this model is flat, as conjectured by Rapoport and Zink, and that its special fibre is reduced.
Borrowing a reduction principle to a recent preprint of G. Faltings (toroidal resolution of some matrix singularities, 1999), we use Lafforgue's compactification of PGL_r^{N+1}/PGL_r to construct a canonical log-smooth toroidal resolution for the bad reduction in a prime p of Shimura varieties of unitary and symplectic type with parahoric level structures at p. Using this result, non-canonical semi-stable resolutions over Z_p[p^{1/ν}] can be derived.
On a conjecture of Pappas and Rapoport
本文证明了帕帕斯和拉波波特关于Shimura型变种的 canonical 整体模型存在性的猜想，并展示了通过整体局部Shimura变种统一同源类，以及证明了Kisin和帕帕斯关于局部模型图的猜想。
On the moduli description of ramified unitary local models of signature $(n-1,1)$
本文在特征非2条件下显式刻画签名 $(n-1,1)$ 分歧酉局部模型的特殊纤维，证实 Smithling 猜想，并推广至 Pappas–Zhu 模型与 Shimura 簇整模型。
Let $E$ be a quadratic imaginary field and let $p$ be a prime which is inert in $E.$ We study three types of Picard modular surfaces in positive characteristic $p$ and the morphisms between them. The first Picard surface, denoted $S$, parametrizes triples $(A,ϕ,ι)$ comprised of an abelian threefold $A$ with an action $ι$ of the ring of integers $\mathcal{O}_{E}$, and a principal polarization $ϕ$. The second surface, $S_{0}(p)$, parametrizes, in addition, a suitably restricted choice of a subgroup $H\subset A[p]$ of rank $p^{2}$. The third Picard surface, $\widetilde{S}$, parametrizes triples $…
We consider the local model of a Shimura variety of PEL type, with the unitary similitudes corresponding to a ramified quadratic extension of $\mathbb{Q}_p$ as defining group. We examine the cases where the level structure at $p$ is given by a parahoric that is the stabilizer of a selfdual periodic lattice chain and that is special in the sense of Bruhat--Tits theory. We prove that in these cases the special fiber of the local model is irreducible and generically reduced; consequently, the special fiber is reduced and is normal, Frobenius split, and with only rational singularities. In additio…
On the Piatetski-Shapiro construction for integral models of Shimura varieties
研究 Piatetski-Shapiro 构造在 Shimura 簇整模型中的应用，证明 Galois 群不动点恢复原簇，并推广至 parahoric 水平及 Igusa 栈。
We investigate the bad reduction of certain Shimura varieties (associated to the symplectic group). More precisely, we look at a model of the Shimura variety at a prime p, with parahoric level structure at p. We show that this model is flat, as conjectured by Rapoport and Zink, and that its special fibre is reduced.
Arithmetic compactifications of integral models of Shimura varieties of abelian type
本文研究了阿贝尔型模形式整数模型的算术紧化，通过构造合适的尖点标记和锥分解，扩展了扭曲构造，并验证了Pink公式。
For any Shimura variety of Hodge type with hyperspecial level at a prime $p$ and a lisse sheaf on it, we prove a formula, conjectured by Kottwitz \cite{Kottwitz90}, for the Lefschetz number of an arbitrary Frobenius-twisted Hecke correspondence acting on the compactly supported étale cohomology and verify another conjecture of Kottwitz \cite{Kottwitz90} on the stabilization of that formula. The main ingredients of our proof of the formula are a recent work of Kisin \cite{Kisin17} on Langlands-Rapoport conjecture and the theory of Galois gerbs developed by Langlands and Rapoport \cite{LR87}. Es…
This paper is a continuation of our paper math.AG/0006222. We study the reduction of certain PEL Shimura varieties with parahoric level structure at primes p at which the group that defines the Shimura variety ramifies. We describe "good" $p$-adic integral models of these Shimura varieties and study their 'etale local structure. In particular, we exhibit a stratification of their (singular) special fibers and give a partial calculation of the sheaf of nearby cycles.
Maximal parahoric arithmetic transfers, resolutions and modularity
本文在非分歧二次 $p$-进扩张中提出并证明极大陪住层级的算术转移猜想及算术基本引理，同时建立算术 theta 级数的新模性结果与 Jacquet–Rallis 转移。
We elaborate the theory of the stable Bernstein center of a $p$-adic group $G$, and apply it to state a general conjecture on test functions for Shimura varieties due to the author and R. Kottwitz. This conjecture provides a framework by which one might pursue the Langlands-Kottwitz method in a very general situation: not necessarily PEL Shimura varieties with arbitrary level structure at $p$. We give a concrete reinterpretation of the test function conjecture in the context of parahoric level structure. We also use the stable Bernstein center to formulate some of the transfer conjectures (the…
Normalization in integral models of Shimura varieties of Hodge type
本文证明Hodge类型Shimura变种的积分模型可通过嵌入到Siegel模形式积分模型中，且标准化步骤冗余，同时扩展到toroidal紧致化的嵌入结果。
On depth-zero integral models of local Shimura varieties
通过指定深度零局部 Shimura 变体中的显式仿射体，其约化为抛物型 Deligne-Lusztig 变体，并在其同调中构造正则深度零超尖表示的 Jacquet-Langlands 对，同时发展局部 shtuka 上深度零层结构的整模空间理论。
We describe the structure of the supersingular locus of a Shimura variety for a quaternionic unitary similitude group of degree $2$ over a ramified odd prime $p$ if the level at $p$ is given by a special maximal compact open subgroup. More precisely, we show that such a locus has purely $2$-dimensional, and every irreducible component is birational to the Fermat surface. Furthermore, we have an estimation of the numbers of connected and irreducible components. To prove these assertions, we completely determine the structure of the underlying reduced scheme of the Rapoport--Zink space for the q…
Moduli descriptions of v-sheaf local models
针对任意仿射群概型parahoric G和任意支配余特征μ，提出v-层局部模型的统一模论描述，采用Tannakian式方法，基于仿射诱导模新理论构建，可解释μ为极小特征时Shimura簇局部模型理论中的线性代数条件。
Canonical extensions of $p$-adic shtukas on toroidal compactifications of Shimura varieties
本文在 Abel 型 Shimura 簇的环面紧化的整模型上，通过研究边界处 shtuka 的“退化”，构造了具有拟抛物水平结构的 $p$-adic shtuka 的典范扩张，并定义了 Pappas-Rapoport 意义下的典范整模型。
In this article we study the Gross-Schoen diagonal cycle on a triple product of Shimura curves at a place of bad reduction. We relate the image of the diagonal cycle under the Abel-Jacobi map to certain period integral that governs the central critical value of the Garrett-Rankin type triple product $L$-function via level raising congruences. As an application we prove certain rank $0$ case of the Bloch-Kato conjecture for the symmetric cube motive of a weight $2$ modular form.
On the geometric connected components of moduli spaces of p-adic shtukas and local Shimura varieties
本文研究了p-adic shtukas模空间与局部Shimura簇的拓扑性质，构造了特殊化映射，并在HN-不可约条件下确定了无限层级模空间的几何连通分支，证明了Rapoport和Viehmann猜想的新情形。
Irreducibility of Local Models
本文研究了带有抛物面水平结构的Shimura簇和$\bG$-Shtuka模空间的局部模型几何特殊纤维的不可约性，分类了局部模型不可约的情况，并证明了不同水平间映射的纤维同构于单个Schubert簇。
On integral local Shimura varieties
本文证明了对于任何阿贝尔类型的(G, μ)，当p≠2或p=2且G为A或C类型时，局部Shimura簇的构造猜想成立，并将其与局部Shimura品种联系起来。
Laumon parahoric local models via quiver Grassmannians
本文利用箭图表示理论研究类型 A 中任意仿抛物子群的 Laumon 局部模型特殊纤维，刻画其不可约分支、自然分层和胞腔分解，并证明奇点消解与仿抛物子群间自然投影相容。
When $p$ is inert in the quadratic imaginary field $E$ and $m<n$, unitary Shimura varieties of signature $(n,m)$ and a hyperspecial level subgroup at $p$, carry a natural foliation of height 1 and rank $m^2$ in the tangent bundle of their special fiber $S$. We study this foliation and show that it acquires singularities at deep Ekedahl-Oort strata, but these singularities are resolved if we pass to a natural smooth moduli problem $S^\sharp$, a successive blow-up of $S$. Over the ($μ$-)ordinary locus we relate the foliation to Moonen's generalized Serre-Tate coordinates. We study the quotient o…
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