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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…

Algebraic Geometry · Mathematics 2020-04-13 Jens Hesse

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…

Algebraic Geometry · Mathematics 2007-05-23 Thomas J. Haines

We consider Shimura varieties associated to a unitary group of signature $(n-s,s)$ where $n$ is even. For these varieties, by using the spin splitting models from Zachos-Zhao, we construct flat, Cohen-Macaulay, and normal $p$-adic integral…

Number Theory · Mathematics 2025-01-13 S. Bijakowski , I. Zachos , Z. Zhao

We study the structure of the supersingular locus of the Rapoport--Zink integral model of the Shimura variety for $\mathrm{GU}(2,2)$ over a ramified odd prime with the special maximal parahoric level. We prove that the supersingular locus…

Number Theory · Mathematics 2021-10-13 Yasuhiro Oki

Local models are schemes, defined in terms of linear algebra, that were introduced by Rapoport and Zink to study the \'etale-local structure of integral models of certain PEL Shimura varieties over p-adic fields. A basic requirement for the…

Algebraic Geometry · Mathematics 2010-03-15 Brian D. Smithling

In this paper we recall the construction and basic properties of complex Shimura varieties and show that these properties actually characterize them. This characterization immediately implies the explicit form of Kazhdan's theorem on the…

Number Theory · Mathematics 2007-05-23 Yakov Varshavsky

In this paper we study the Newton stratification on the reduction of Shimura varieties of PEL type with hyperspecial level structure and the Newton stratification on the deformation space of a Barsotti-Tate group with PEL structure. Our…

Algebraic Geometry · Mathematics 2017-03-10 Paul Hamacher

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…

Number Theory · Mathematics 2021-05-14 Yasuhiro Oki

We study some integral model of P.E.L. Shimura varieties of type A for ramified primes. Precisely, we look at the Pappas-Rapoport model (or splitting model) of some unitary Shimura varieties for which there is ramification in the degree 2…

Algebraic Geometry · Mathematics 2024-01-17 Stéphane Bijakowski , Valentin Hernandez

We consider Shimura varieties associated to a unitary group of signature $(2,n-2)$. We give regular $p$-adic integral models for these varieties over odd primes $p$ which ramify in the imaginary quadratic field with level subgroup at $p$…

Number Theory · Mathematics 2024-09-25 Ioannis Zachos

We study the special fiber of the integral models for Shimura varieties of Hodge type with parahoric level structure constructed by Kisin and Pappas in [KP]. We show that when the group is residually split, the points in the mod $p$ isogeny…

Number Theory · Mathematics 2020-12-23 Rong Zhou

In this paper, we compare two cohomology groups associated to Shimura varieties of PEL type, which are not proper over the base. One is the compactly supported l-adic cohomology, and the other is the nearby cycle cohomology, namely, the…

Number Theory · Mathematics 2011-09-26 Naoki Imai , Yoichi Mieda

We consider unitary Shimura varieties at places where the totally real field ramifies over $\mbQ$. Our first result constructs comparison isomorphisms between absolute and relative local models in this context, which relies on a…

Algebraic Geometry · Mathematics 2025-09-10 Yu Luo , Andreas Mihatsch , Zhiyu Zhang

We prove the geometrical Satake isomorphism for a reductive group defined over F=k((t)), and split over a tamely ramified extension. As an application, we give a description of the nearby cycles on certain Shimura varieties via the…

Representation Theory · Mathematics 2013-01-01 Xinwen Zhu

We consider Shimura varieties for orthogonal or spin groups acting on hermitian symmetric domains of type IV. We give regular p-adic integral models for these varieties over odd primes p at which the level subgroup is the connected…

Number Theory · Mathematics 2021-12-16 Georgios Pappas , Ioannis Zachos

We propose a conjectural theory of $p$-integral models of Shimura varieties with level structure at $p$ given by a class of normal subgroups of parahoric subgroups with abelian quotient group. The role of the theory of local models is…

Algebraic Geometry · Mathematics 2026-04-08 Georgios Pappas , Michael Rapoport

We study the reduction of certain integral models of Shimura varieties of PEL type with Iwahori level structure. On these spaces we have the Kottwitz-Rapoport and the $p$-rank stratification. We show that the $p$-rank is constant on a KR…

Algebraic Geometry · Mathematics 2012-10-05 Philipp Hartwig

Let $p$ be an odd prime and $F$ be a complete discretely valued field with residue field of characteristic $p$. For any parahoric level structure of the split even orthogonal similitude group $\operatorname{GO}_{2n}$ over $F$, we prove a…

Number Theory · Mathematics 2025-12-19 Jie Yang

We introduce a notion of full level structure for the group scheme $\mu_p \times \mu_p$, and show that scheme of full level structures is flat over $\Bbb{Z}$.

Number Theory · Mathematics 2018-06-19 Preston Wake

We prove in this paper a classicality result for overconvergent modular forms on PEL Shimura varieties of type (A) or (C), without any ramification hypothesis. We use an analytic continuation method, which generalizes previous results in…

Number Theory · Mathematics 2017-04-24 Stéphane Bijakowski