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Local cohomology of Du Bois singularities and applications to families

Part of: Local theory (Co)homology theory General commutative ring theory

Published online by Cambridge University Press:  27 July 2017

Linquan Ma ,
Karl Schwede  and
Kazuma Shimomoto
Linquan Ma
Affiliation:
Department of Mathematics, University of Utah, Salt Lake City, UT 84112, USA email [email protected]
Karl Schwede
Affiliation:
Department of Mathematics, University of Utah, Salt Lake City, UT 84112, USA email [email protected]
Kazuma Shimomoto
Affiliation:
Department of Mathematics, College of Humanities and Sciences, Nihon University, Setagaya-ku, Tokyo 156-8550, Japan email [email protected]
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Abstract

In this paper we study the local cohomology modules of Du Bois singularities. Let $(R,\mathfrak{m})$ be a local ring; we prove that if $R_{\text{red}}$ is Du Bois, then $H_{\mathfrak{m}}^{i}(R)\rightarrow H_{\mathfrak{m}}^{i}(R_{\text{red}})$ is surjective for every $i$. We find many applications of this result. For example, we answer a question of Kovács and Schwede [Inversion of adjunction for rational and Du Bois pairs, Algebra Number Theory 10 (2016), 969–1000; MR 3531359] on the Cohen–Macaulay property of Du Bois singularities. We obtain results on the injectivity of $\operatorname{Ext}$ that provide substantial partial answers to questions in Eisenbud et al. [Cohomology on toric varieties and local cohomology with monomial supports, J. Symbolic Comput. 29 (2000), 583–600] in characteristic $0$. These results can also be viewed as generalizations of the Kodaira vanishing theorem for Cohen–Macaulay Du Bois varieties. We prove results on the set-theoretic Cohen–Macaulayness of the defining ideal of Du Bois singularities, which are characteristic-$0$ analogs and generalizations of results of Singh–Walther and answer some of their questions in Singh and Walther [On the arithmetic rank of certain Segre products, in Commutative algebra and algebraic geometry, Contemporary Mathematics, vol. 390 (American Mathematical Society, Providence, RI, 2005), 147–155]. We extend results on the relation between Koszul cohomology and local cohomology for $F$-injective and Du Bois singularities first shown in Hochster and Roberts [The purity of the Frobenius and local cohomology, Adv. Math. 21 (1976), 117–172; MR 0417172 (54 #5230)]. We also prove that singularities of dense $F$-injective type deform.

Keywords

Du BoisCohen–MacaulayF-injectivelocal cohomology

MSC classification

Primary: 14F17: Vanishing theorems 13A35: Characteristic $p$ methods (Frobenius endomorphism) and reduction to characteristic $p$; tight closure 14F18: Multiplier ideals 14B05: Singularities
Type
Research Article
Information
Compositio Mathematica , Volume 153 , Issue 10 , October 2017 , pp. 2147 - 2170
Copyright
© The Authors 2017 

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