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arXiv 2103.07209math.AG
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由 ${\bb C}^*$-作用产生的Mori dream空间的小修正

Small modifications of Mori dream spaces arising from ${\mathbb C}^*$-actions

Gianluca Occhetta, Eleonora A. Romano, Luis E. Solá Conde, Jarosław A. Wiśniewski

AI总结:

本研究将带 ${\bb C}^*$-作用的射影簇小修正与GIT商关联,用Białynicki-Birula胞腔闭包处的flip构造双有理等变修正,完整刻画特定光滑簇的吹张修正结构,并给出齐性簇上的构造实例。

摘要:

我们将带有 ${\bb C}^*$-作用的射影簇的小修正与其GIT商联系起来。具体而言,利用中心位于Białynicki-Birula胞腔闭包中的flip(翻转),我们构造了原簇的一族双有理等变修正,其中包含那些使得商映射可从半稳定点集延拓为正则态射的修正。对于Picard数为1、带有 ${\bb C}^*$-作用且任意点都没有有限迷向子群的光滑簇,我们完整描述了沿汇点和源点进行吹张的修正结构。相关例子可在带有 ${\bb C}^*$-作用的齐性簇上构造,该作用与其李代数的短分次相关。

英文摘要:

We link small modifications of projective varieties with a ${\mathbb C}^*$-action to their GIT quotients. Namely, using flips with centers in closures of Białynicki-Birula cells, we produce a system of birational equivariant modifications of the original variety, which includes those on which a quotient map extends from a set of semistable points to a regular morphism. The structure of the modifications is completely described for the blowup along the sink and the source of smooth varieties with Picard number one with a ${\mathbb C}^*$-action which has no finite isotropy for any point. Examples can be constructed upon homogeneous varieties with a ${\mathbb C}^*$-action associated to short grading of their Lie algebras.

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