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arXiv math/9910021math.AG
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全纯辛四重上的有理曲线

Rational curves on holomorphic symplectic fourfolds

Brendan Hassett, Yuri Tschinkel

摘要:

设F是一个极化的不可约全纯辛四重,变形等价于Hilbert方案参数化长度为两个零维子计划的K3曲面。同调群H^2(F,Z)具有一个整数对称非退化形式,即Beauville形式。我们给出了精确的结构的锥的有效曲线-和对偶-锥的充分因子。形式上,它们完全类似于已知的K3曲面的结果,并且它们完全用限制于Pic(F)的Beauville形式表示的整数来表示。利用形变理论证明了这些定理在模空间的开子集中成立。包含在三次四重中的线的法诺簇是全纯辛四重的一个例子。我们的图解包含了许多关于三次四重的具体几何陈述,这些陈述可以用射影几何来验证。

英文摘要:

Let F be a polarized irreducible holomorphic symplectic fourfold, deformation equivalent to the Hilbert scheme parametrizing length-two zero-dimensional subschemes of a K3 surface. The homology group H^2(F,Z) is equipped with an integral symmetric nondegenerate form, the Beauville form. We give precise conjectures for the structure of the cone of effective curves - and by duality - the cone of ample divisors. Formally they are completely analogous to the results known for K3 surfaces, and they are expressed entirely in terms of the integers represented by the Beauville form restricted to Pic(F). We prove that these conjectures are true in an open subset of the moduli space using deformation theory. The Fano variety of lines contained in a cubic fourfold is an example of a holomorphic symplectic fourfold. Our conjectures imply many concrete geometric statements about cubic fourfolds which may be verified using projective geometry.

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