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arXiv 1010.3755math.AGmath.CO
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线丛例外序列的最大长度

Maximal lengths of exceptional collections of line bundles

Alexander I. Efimov

AI总结:

本文通过构造无穷多皮卡德数三的环面法诺簇反例否定 King 猜想,并证明线丛例外序列最大长度的最优下界常数为 3/4。

摘要:

本文构造了无穷多个具有皮卡德数三的环面法诺簇的例子,这些簇不承认线丛的完全例外序列。特别地,这否定了关于环面法诺簇的 King 猜想。更一般地,我们证明对任意常数 $c>\ rac34$,存在无穷多个皮卡德数三的环面法诺簇 $Y$,使得 $Y$ 上线丛例外序列的最大长度严格小于 $c\ k K_0(Y)$。要得到没有线丛例外序列的簇,只需取 $c=1$。另一方面,我们证明对任意皮卡德数三的环面 nef-Fano DM 栈 $Y$,其上存在长度至少为 $\ rac34 \ k K_0(Y)$ 的线丛强例外序列。因此常数 $\ rac34$ 在此性质下是最大的。

英文摘要:

In this paper we construct infinitely many examples of toric Fano varieties with Picard number three, which do not admit full exceptional collections of line bundles. In particular, this disproves King's conjecture for toric Fano varieties. More generally, we prove that for any constant $c>\frac34$ there exist infinitely many toric Fano varieties $Y$ with Picard number three, such that the maximal length of exceptional collection of line bundles on $Y$ is strictly less than $c\rk K_0(Y).$ To obtain varieties without exceptional collections of line bundles, it suffices to put $c=1.$ On the other hand, we prove that for any toric nef-Fano DM stack $Y$ with Picard number three, there exists a strong exceptional collection of line bundles on $Y$ of length at least $\frac34 \rk K_0(Y).$ The constant $\frac34$ is thus maximal with this property.

机构、总结、中文摘要均由AI分析而来,可能存在错误,请以论文正文为准。

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