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Extensors and the Hilbert scheme

Abstract : The Hilbert scheme $Hilb_{p(t)}^n$ parametrizes closed subschemes and families of closed subschemes in the projective space $P^n$ with a fixed Hilbert polynomial $p(t)$. It is classically realized as a closed subscheme of a Grassmannian or a product of Grassmannians. In this paper we present a method that allows to derive scheme theoretical global equations for $Hilb_{p(t)}^n$ in the Plücker coordinates of a Grassmannian $Grass_p^N$, where $p$ and $N$ depend on the dimension $n$ of the projective space and on the Hilbert polynomial $p(t)$. Using this method we obtain the already known set of equations given by Iarrobino and Kleiman in 1999, the one conjectured by Bayer in 1982 and proved by Haiman and Sturmfels in 2004, and also a new set of equations of degree lower than the previous ones. The novelties of our approach are essentially two. The first one is a "local" study of the Hilbert functor through special sets of open subfunctors obtained exploiting the symmetries of the Hilbert scheme and the combinatorial properties of monomial ideals, mainly the Borel-fixed ones. The second one is a generalization of the theory of extensors to the setting of free modules over any ring $A$ and the description of any exterior product of elements of a free submodule in terms of Plücker coordinates.
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Contributor : Bernard Mourrain Connect in order to contact the contributor
Submitted on : Monday, April 22, 2013 - 2:13:35 PM
Last modification on : Monday, August 29, 2022 - 11:40:38 AM

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Jerome Brachat, Paolo Lella, Bernard Mourrain, Margherita Roggero. Extensors and the Hilbert scheme. Annali della Scuola Normale Superiore di Pisa, Classe di Scienze, 2014, pp. 23. ⟨10.2422/2036-2145.201407_003⟩. ⟨hal-00816528⟩



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