Searcharxiv⌕ Search

arXiv · 0705.2927

Inductive characterizations of hyperquadrics

Abstract

We give two characterizations of hyperquadrics: one as non-degenerate smooth projective varieties swept out by large dimensional quadric subvarieties passing through a point; the other as $LQEL$-manifolds with large secant defects.

Explore related subjects

Keep this discovery

Explore connections, maps & timelines

BibTeXRIS

Baohua Fu. 2007-05-21. Inductive characterizations of hyperquadrics. https://arxiv.org/abs/0705.2927

Cite the original work for its findings. Save a collection to share your selection of sources.

KEEP EXPLORING

Related papers

Adjoint test modules along Cohen--Macaulay morphisms

We provide a transformation rule for adjoint test modules along Cohen--Macaulay maps between Cohen--Macaulay varieties that have $F$-rational geometric fibers. This is, in part, an effective version of Enescu's theorem on the ascent of $F$-rationality under local maps with $F$-rational geometric fibers.

math.AG↗

Limits of Hyperkähler Manifolds and Moduli Spaces of Sheaves on K3 Surfaces

We prove that a compact strongly Gauduchon manifold which is a limit of compact hyperkähler manifolds is bimeromorphic to a compact hyperkähler manifold. This settles a case of a conjecture of Soldatenkov and Verbitsky. A closed completion of a Gauduchon metric bounds the Dirichlet energies of nearby biholomorphisms. This bound yields a meromorphic limit map, which has degree one and is therefore a bimeromorphism onto a compact hyperkähler manifold. We apply this result to moduli spaces of stable torsion-free coherent sheaves on K3 surfaces. A Bott--Chern diagonal formula gives the $\partial\bar\partial$-lemma, and positivity of determinant classes gives Kählerness, proving Perego's conjecture.

math.AG↗

Algebraic loops, braids, and tropicalization

Let $Y$ be a smooth complex algebraic variety. We develop a tropical framework for studying algebraic loops, i.e., free homotopy classes in $Y^{\mathrm{an}}$ associated with formal loops $\mathrm{Spec}\, \mathbb{C}(\!(t)\!)\to Y$. When $Y$ is very affine, every formal loop determines an integral point of $\mathrm{Trop}(Y)$. For schön varieties, we prove that the associated algebraic loop is determined by this tropical point together with a connected component of the corresponding initial variety. Consequently, when all initial varieties are connected, integral tropical points classify algebraic loops. We apply this theory to the case when $Y$ is a hyperplane arrangement complement. In this case, we identify the initial varieties with complements of graded arrangements and obtain explicit representatives for algebraic loops as products of relative full twists. In type $A$, these representatives recover pure algebraic braids. For root arrangements, our construction gives a tropical interpretation of the split root valuation data of Goresky, Kottwitz, and MacPherson. Finally, we prove that the cohomology of braid varieties associated with positive algebraic braids depends only on their root valuation data.

math.AG↗