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We form a generating series of regularized volumes of intersections of special cycles on a non-compact unitary Shimura variety with a fixed base change cycle. We show that it is a Hilbert modular form by identifying it with a theta…

Number Theory · Mathematics 2017-10-17 Zavosh Amir-Khosravi

We construct local models of Shimura varieties and investigate their singularities, with special emphasis on wildly ramified cases. More precisely, with the exception of odd unitary groups in residue characteristic $2$ we construct local…

Algebraic Geometry · Mathematics 2024-12-24 Najmuddin Fakhruddin , Thomas Haines , João Lourenço , Timo Richarz

We study special cycles on a Shimura variety of orthogonal type over a totally real field of degree $d$ associated with a quadratic form in $n+2$ variables whose signature is $(n,2)$ at $e$ real places and $(n+2,0)$ at the remaining $d-e$…

Number Theory · Mathematics 2022-04-29 Yota Maeda

The paper has two parts. First we prove that the specialization maps on R-equivalence and on the Chow group of zero cycles are isomorphisms for families over a local, Henselian, Dedekind ring when the special fiber is smooth and separably…

Algebraic Geometry · Mathematics 2007-05-23 János Kollár

We provide a moduli description of the ramified unitary local model of signature $(n-1,1)$ with arbitrary parahoric level structure, assuming the residue field has characteristic not equal to $2$, thereby confirming a conjecture of…

Algebraic Geometry · Mathematics 2025-05-14 Yu Luo

Structural properties of unitary groups over local, not necessarily commutative, rings are developed, with applications to the computation of the orders of these groups (when finite) and to the degrees of the irreducible constituents of the…

Group Theory · Mathematics 2013-03-22 J. Cruickshank , A. Herman , R. Quinlan , F. Szechtman

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…

Algebraic Geometry · Mathematics 2009-09-25 U. Goertz

In this note, we consider special algebraic cycles on the Shimura variety S associated to a quadratic space V over a totally real field F, |F:\Q|=d, of signature ((m,2)^{d_+},(m+2,0)^{d-d_+}), 1\le d_+<d. For each n, 1\le n\le m, there are…

Number Theory · Mathematics 2022-02-09 Stephen Kudla

Let $K$ be a periodic cell complex endowed with a covering $q:K\to G$ where $G$ is a finite quotient space of equivalence classes under translations acting on $K$. We assume $G$ is embedded in a space whose homotopy type is a $d$-torus for…

Algebraic Topology · Mathematics 2025-09-19 Adam Onus , Primoz Skraba

Let $F$ be a real quadratic field in which a fixed prime $p$ is inert, and $E_0$ be an imaginary quadratic field in which $p$ splits; put $E=E_0 F$. Let ${{\rm Sh}}_{1,n-1}$ be the special fiber over $\mathbb{F}_{p^2}$ of the Shimura…

Number Theory · Mathematics 2026-01-21 Zijie Tao

For a Shimura variety of Hodge type with hyperspecial level structure at a prime $p$, Vasiu and Kisin constructed a smooth integral model (namely the integral canonical model) uniquely determined by a certain extension property. We define…

Algebraic Geometry · Mathematics 2017-07-05 Chao Zhang

The paper is a continuation of the paper of Kudla-Rapoport-Zink on $p$-adic uniformization of Shimura curves associated to a group of binary unitary similitudes. Here we consider two variants: first, the RSZ variant, for which we can allow…

Number Theory · Mathematics 2026-05-20 Michael Rapoport , Haining Wang

We study the intersections of special cycles on a unitary Shimura variety of signature (n-1,1), and show that the intersection multiplicities of these cycles agree with Fourier coefficients of Eisenstein series. The results are new cases of…

Number Theory · Mathematics 2013-03-05 Benjamin Howard

The Kodaira dimension of Shimura varieties has been studied by many people. Kondo and Gritsenko-Hulek-Sankaran studied the singularities of orthogonal Shimura varieties related to the moduli spaces of polarized K3 surfaces. They proved that…

Number Theory · Mathematics 2022-04-05 Yota Maeda

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…

Algebraic Geometry · Mathematics 2018-04-16 M. Kisin , G. Pappas

We consider families of special cycles, as introduced by Kudla, on Shimura varieties attached to anisotropic quadratic spaces over totally real fields. By augmenting these cycles with Green currents, we obtain classes in the arithmetic Chow…

Number Theory · Mathematics 2026-01-14 Siddarth Sankaran

I employ methods from derived algebraic geometry to give a uniform moduli-theoretic construction of special cycle classes on integral models many Shimura varieties of Hodge type, including unitary, quaternionic, and orthogonal Shimura…

Number Theory · Mathematics 2023-06-05 Keerthi Madapusi

Let $p:X \rightarrow S$ be a flat, proper and regular scheme over a strictly henselian discrete valuation ring. We prove that the singularity category of the special fiber with its natural two-periodic structure allows to recover the…

Algebraic Geometry · Mathematics 2024-12-17 Dario Beraldo , Massimo Pippi

We show that the span of special cycles in the $r$th Chow group of a Shimura variety of orthogonal type is finite dimensional, if $r < 5$. As our main tool, we develop the theory of Jacobi forms with rational index $M \in \Mat{N}(\QQ)$.

Number Theory · Mathematics 2013-04-04 Martin Raum

In this article, we prove results about the cohomology of compact unitary group Shimura varieties at split places. In nonendoscopic cases, we are able to give a full description of the cohomology, after restricting to integral Hecke…

Algebraic Geometry · Mathematics 2011-10-04 Peter Scholze , Sug Woo Shin