On Severi varieties as intersections of a minimum number of quadrics

Hendrik Van Maldeghem; Magali Victoor

doi:10.56754/0719-0646.2402.0307

DOI:

https://doi.org/10.56754/0719-0646.2402.0307

Abstract

Let \({\mathscr{V}}\) be a variety related to the second row of the Freudenthal-Tits Magic square in \(N\)-dimensional projective space over an arbitrary field. We show that there exist \(M\leq N\) quadrics intersecting precisely in \({\mathscr{V}}\) if and only if there exists a subspace of projective dimension \(N-M\) in the secant variety disjoint from the Severi variety. We present some examples of such subspaces of relatively large dimension. In particular, over the real numbers we show that the Cartan variety (related to the exceptional group \({E_6}\)\((\mathbb R)\)) is the set-theoretic intersection of 15 quadrics.

Keywords

Cartan variety , quadrics , exceptional geometry , Severi variety , quaternion veronesian

Hendrik Van Maldeghem Ghent University, Department of Mathematics: Algebra & Geometry, Krijgslaan 281, S25, B-9000 Gent, Belgium.
Magali Victoor Ghent University, Department of Mathematics: Algebra & Geometry, Krijgslaan 281, S25, B-9000 Gent, Belgium.

Pages: 307–331
Date Published: 2022-08-22
Vol. 24 No. 2 (2022)

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