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arXiv · 1509.03954

Local cohomology with support in ideals of symmetric minors and Pfaffians

Claudiu Raicu·Jerzy Weyman
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Abstract

We compute the local cohomology modules H_Y^(X,O_X) in the case when X is the complex vector space of n x n symmetric, respectively skew-symmetric matrices, and Y is the closure of the GL-orbit consisting of matrices of any fixed rank, for the natural action of the general linear group GL on X. We describe the D-module composition factors of the local cohomology modules, and compute their multiplicities explicitly in terms of generalized binomial coefficients. One consequence of our work is a formula for the cohomological dimension of ideals of even minors of a generic symmetric matrix: in the case of odd minors, this was obtained by Barile in the 90s. Another consequence of our work is that we obtain a description of the decomposition into irreducible GL-representations of the local cohomology modules (the analogous problem in the case when X is the vector space of m x n matrices was treated in earlier work of the authors).

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Claudiu Raicu, Jerzy Weyman. 2015-09-14. Local cohomology with support in ideals of symmetric minors and Pfaffians. https://doi.org/10.1112/jlms%2Fjdw056

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