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arXiv 1610.04077math.AG
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含缺陷超曲面

Hypersurfaces with defect

Niels Lindner

摘要:

在适当的上同调理论中,如果对于某些$i \in \{n, \dots, 2n-2\}$,射影超曲面$X \subseteq \mathbb P^n$有缺陷,则$h^i(X) \neq h^i(\mathbb P^n)$.例如,当$X \subseteq \mathbb P^4$不是$\mathbb Q$阶乘时,就会发生这种情况。我们证明了在特征为0时,含缺陷超曲面的Tjurina数是大的。对于具有轻度奇异性的$X$,在正特征上也有类似的结果.作为应用,我们得到了有限域上无亏损超曲面的渐近密度的一个下界。

英文摘要:

A projective hypersurface $X \subseteq \mathbb P^n$ has defect if $h^i(X) \neq h^i(\mathbb P^n)$ for some $i \in \{n, \dots, 2n-2\}$ in a suitable cohomology theory. This occurs for example when $X \subseteq \mathbb P^4$ is not $\mathbb Q$-factorial. We show that in characteristic 0, the Tjurina number of hypersurfaces with defect is large. For $X$ with mild singularities, there is a similar result in positive characteristic. As an application, we obtain a lower bound on the asymptotic density of hypersurfaces without defect over a finite field.

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