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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…

Algebraic Geometry · Mathematics 2012-11-27 G. Pappas , X. Zhu

Kottwitz conjectured a formula for the (semi-simple) trace of Frobenius on the nearby cycles for the local model of a Shimura variety with Iwahori-type level structure. In this paper, we prove his conjecture in the linear and symplectic…

Algebraic Geometry · Mathematics 2007-05-23 T. Haines , B. C. Ngo

We extend the group theoretic construction of local models of Pappas and Zhu to the case of groups obtained by Weil restriction along a possibly wildly ramified extension. This completes the construction of local models for all reductive…

Number Theory · Mathematics 2019-02-20 Brandon Levin

In this paper, we compute the cohomology sheaves of the $\ell$-adic nearby cycles on the local model of the PEL $\mathrm{GU}(n-1,1)$ Shimura variety over a ramified prime, with level given by the stabilizer of a self-dual lattice. This…

Number Theory · Mathematics 2026-05-21 Joseph Muller

We prove the test function conjecture of Kottwitz and the first named author for local models of Shimura varieties with parahoric level structure attached to Weil-restricted groups, as defined by B. Levin. Our result covers the (modified)…

Algebraic Geometry · Mathematics 2020-07-08 Thomas J. Haines , Timo Richarz

We compute the trace of Frobenius on the sheaf of nearby cycles for the integral model of the Siegel modular variety with pro-p Iwahori level structure, constructed by Haines and Stroh, in the case of $\text{GSp}_4$. To this end, we make…

Algebraic Geometry · Mathematics 2026-05-27 Giulio Marazza

Using the Langlands-Kottwitz paradigm, we compute the trace of Frobenius composed with Hecke operators on the cohomology of nearby cycles, at places of parahoric reduction, of perverse sheaves on certain moduli stacks of shtukas. Following…

Number Theory · Mathematics 2020-02-12 Tony Feng

We prove a number of results on the \'etale cohomology of rigid analytic varieties over $p$-adic non-archimedean local fields. Among other things, we establish bounds for Frobenius eigenvalues, show a strong version of Grothendieck's local…

Algebraic Geometry · Mathematics 2025-07-21 David Hansen , Bogdan Zavyalov

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 define and study a collection of special cycles on certain non-PEL Shimura varieties for $U(2,1) \times U(1,1)$ that appear naturally in the context of the recent conjectures of Gan, Gross and Prasad on restrictions of automorphic forms…

Number Theory · Mathematics 2016-10-07 Dimitar P. Jetchev

Kottwitz's conjecture describes the contribution of a supercuspidal represention to the cohomology of a local Shimura variety in terms of the local Langlands correspondence. A natural extension of this conjecture concerns Scholze's more…

Number Theory · Mathematics 2022-03-21 Tasho Kaletha , David Hansen , Jared Weinstein

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

The Kottwitz conjecture describes the cohomology of basic Rapoport-Zink spaces using local Langlands correspondences. In this paper, via geometrical studies of some Kottwitz-type Shimura varieties, we prove this conjecture for basic simple…

Number Theory · Mathematics 2022-04-15 Kieu Hieu Nguyen

In this paper we study the cohomology of PEL-type Rapoport-Zink spaces associated to unramified unitary similitude groups over $\Q_p$ in an odd number of variables. We extend the results of Kaletha-Minguez-Shin-White to construct a local…

Number Theory · Mathematics 2021-07-01 Alexander Bertoloni Meli , Kieu Hieu Nguyen

We study unramified unitary and unitary similitude groups in an odd number of variables. Using work of the first and third named authors on the Kottwitz Conjecture for the similitude groups, we show that the Fargues--Scholze local Langlands…

Number Theory · Mathematics 2024-04-22 Alexander Bertoloni Meli , Linus Hamann , Kieu Hieu Nguyen

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

In this paper we generalize and study a notion of (unipotent) nearby cycles over a higher dimensional base based on Be\u{i}linson's description of unipotent nearby cycles, following an idea of Gaitsgory. This generalization, in the setting…

Algebraic Geometry · Mathematics 2024-02-01 Pramod N. Achar , Simon Riche

In this article, we study local models associated to certain Shimura varieties. In particular, we present a resoultion of their singularities. As a consequence, we are able to determine the alternating semisimple trace of the geometric…

Algebraic Geometry · Mathematics 2007-05-23 Nicole Kraemer

The paper is concerned with cohomology of the small quantum group at a root of unity, and of its upper triangular subalgebra, with coefficients in a tilting module. We relate it to a certain t-structure on the derived category of…

Representation Theory · Mathematics 2007-05-23 Roman Bezrukavnikov

We study the Scholze test functions for bad reduction of simple Shimura varieties at a prime where the underlying local group is any inner form of a product of Weil restrictions of general linear groups. Using global methods, we prove that…

Number Theory · Mathematics 2025-02-04 Jingren Chi , Thomas J. Haines
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