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Topological flatness of local models for ramified unitary groups. II. The even dimensional case

Part of: Algebraic combinatorics Arithmetic problems. Diophantine geometry

Published online by Cambridge University Press:  10 July 2013

Brian D. Smithling
Brian D. Smithling*
Affiliation:
Johns Hopkins University, Department of Mathematics, 3400 N. Charles St., Baltimore, MD 21218, USA ([email protected])
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Abstract

Local models are schemes, defined in terms of linear-algebraic moduli problems, which are used to model the étale-local structure of integral models of certain $p$-adic PEL Shimura varieties defined by Rapoport and Zink. In the case of a unitary similitude group whose localization at ${ \mathbb{Q} }_{p} $ is ramified, quasi-split $G{U}_{n} $, Pappas has observed that the original local models are typically not flat, and he and Rapoport have introduced new conditions to the original moduli problem which they conjecture to yield a flat scheme. In a previous paper, we proved that their new local models are topologically flat when $n$ is odd. In the present paper, we prove topological flatness when $n$ is even. Along the way, we characterize the $\mu $-admissible set for certain cocharacters $\mu $ in types $B$ and $D$, and we show that for these cocharacters admissibility can be characterized in a vertexwise way, confirming a conjecture of Pappas and Rapoport.

Keywords

local modelShimura varietyunitary groupIwahori–Weyl groupadmissible set

MSC classification

Secondary: 14G35: Modular and Shimura varieties 05E15: Combinatorial aspects of groups and algebras
Type
Research Article
Information
Journal of the Institute of Mathematics of Jussieu , Volume 13 , Issue 2 , April 2014 , pp. 303 - 393
Copyright
©Cambridge University Press 2013 

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