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On the closure of the Hodge locus of positive period dimension
Inventiones mathematicae ( IF 2.6 ) Pub Date : 2021-03-29 , DOI: 10.1007/s00222-021-01042-4
B. Klingler , A. Otwinowska

Given \({{\mathbb {V}}}\) a polarizable variation of \({{\mathbb {Z}}}\)-Hodge structures on a smooth connected complex quasi-projective variety S, the Hodge locus for \({{\mathbb {V}}}^\otimes \) is the set of closed points s of S where the fiber \({{\mathbb {V}}}_s\) has more Hodge tensors than the very general one. A classical result of Cattani, Deligne and Kaplan states that the Hodge locus for \({{\mathbb {V}}}^\otimes \) is a countable union of closed irreducible algebraic subvarieties of S, called the special subvarieties of S for \({{\mathbb {V}}}\). Under the assumption that the adjoint group of the generic Mumford–Tate group of \({{\mathbb {V}}}\) is simple we prove that the union of the special subvarieties for \({{\mathbb {V}}}\) whose image under the period map is not a point is either a closed algebraic subvariety of S or is Zariski-dense in S. This implies for instance the following typical intersection statement: given a Hodge-generic closed irreducible algebraic subvariety S of the moduli space \({{\mathcal {A}}}_g\) of principally polarized Abelian varieties of dimension g, the union of the positive dimensional irreducible components of the intersection of S with the strict special subvarieties of \({{\mathcal {A}}}_g\) is either a closed algebraic subvariety of S or is Zariski-dense in S.



中文翻译:

关于正周期维数Hodge轨迹的封闭

给定\({{\ mathbb {V}}} \)可极化\\ {{\ mathbb {Z}}} \)-光滑连接的复拟投影变体S上的霍奇结构,它是\的霍奇轨迹。 ({{\ mathbb {V}}} ^ \ otimes \)S的闭合点s集合,其中光纤\({{\ mathbb {V}}} _ s \)的Hodge张量比一般的张量更多。 。Cattani,德利涅和Kaplan的一个经典的结果指出,霍奇轨迹为\({{\ mathbb {V}}} ^ \ otimes \)是闭合的不可约代数子簇的可数工会小号,称为特殊子簇小号\({{\ mathbb {V}}} \)。假设\({{\ mathbb {V}}} \)的通用Mumford–Tate组的伴随组很简单,我们证明\({{\ mathbb {V}}的特殊子变量的并集} \)的期间地图下,其图像是不是一个点或者是一个封闭的代数subvariety小号或是Zariski密集在小号。例如,这意味着以下典型的交集语句:给定一个主要极化的尺寸为g的阿贝尔变数的模空间\({{{\ mathcal {A}}} _ g \)的Hodge-generic闭合不可约代数子变量S,其并集为S交点的正维不可约分量与严格特殊子簇\({{\ mathcal {A}}} _克\)或者是一个封闭的代数subvariety小号或是Zariski密集在小号

更新日期:2021-03-29
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