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$K({\it\pi},1)$-neighborhoods and comparison theorems

Part of: (Co)homology theory

Published online by Cambridge University Press:  05 June 2015

Piotr Achinger
Piotr Achinger*
Affiliation:
Department of Mathematics, University of California, Berkeley, CA 94720, USA email [email protected]
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Abstract

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A technical ingredient in Faltings’ original approach to $p$-adic comparison theorems involves the construction of $K({\it\pi},1)$-neighborhoods for a smooth scheme $X$ over a mixed characteristic discrete valuation ring with a perfect residue field: every point $x\in X$ has an open neighborhood $U$ whose generic fiber is a $K({\it\pi},1)$ scheme (a notion analogous to having a contractible universal cover). We show how to extend this result to the logarithmically smooth case, which might help to simplify some proofs in $p$-adic Hodge theory. The main ingredient of the proof is a variant of a trick of Nagata used in his proof of the Noether normalization lemma.

Keywords

Faltings’ toposétale cohomologylogarithmic geometrysemistable reductionp-adic Hodge theoryK (𝜋, 1) schemes

MSC classification

Primary: 14F20: Étale and other Grothendieck topologies and (co)homologies
Secondary: 14F30: $p$-adic cohomology, crystalline cohomology
Type
Research Article
Information
Compositio Mathematica , Volume 151 , Issue 10 , October 2015 , pp. 1945 - 1964
Copyright
© The Author 2015 

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