arXivDaily arXiv每日学术速递 周一至周五更新
arXiv 2007.13841math.AG
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三章克雷莫纳集团

Three chapters on Cremona groups

Serge Cantat, Julie Déserti, Junyi Xie

摘要:

在本文的第一部分,我们回答了一个问题,我。Dolgachev提出了一个新的正则化问题,它涉及到:给定一个双有理映射$f\in\mathrm{Bir}(\mathbb{P}^m_\mathbf{k})$和一个线性射影映射$A\in\mathrm{PGL}_{m+1}(\mathbf{k})$,$A\circ f$何时可正则化?Dolgachev最初的问题是,这是否会发生在$\mathrm{PGL}_{m+1}(\mathbf{k})$中的所有$A$上,答案是否定的。然后我们看序列$n\mapsto\mathrm{deg}\, f^n$,$f\in\mathrm{Bir}(\mathbb{P}^2_\mathbf{k})$。我们表明,有没有约束的序列$n\mapsto\mathrm{deg}\, f^n-\mathrm{deg}\, f^{n-1}$的小值$n$。最后研究了双有理映射不变曲线束的次数。当f是一个Hessen或Jonquières扭曲,我们证明了这个程度是有界的$\mathrm{deg}\, f$的功能。我们推导出的共轭类的结构上的推论,和它们的性质相对于Zaperki拓扑的$\mathrm{Bir}(\mathbb{P}^2_\mathbf{k})$。

英文摘要:

In the first part of this article, we answer a question of I. Dolgachev, which is related to the following problem: given a birational map $f\in\mathrm{Bir}(\mathbb{P}^m_\mathbf{k})$ and a linear projective map $A\in\mathrm{PGL}_{m+1}(\mathbf{k})$, when is $A\circ f$ regularizable? Dolgachev's initial question is whether this may happen for all $A$ in $\mathrm{PGL}_{m+1}(\mathbf{k})$, and the answer is negative. We then look at the sequence $n\mapsto\mathrm{deg}\, f^n$, $f\in\mathrm{Bir}(\mathbb{P}^2_\mathbf{k})$. We show that there is no constraint on the sequence $n\mapsto\mathrm{deg}\, f^n-\mathrm{deg}\, f^{n-1}$ for small values of $n$. Finally we study the degree of pencils of curves which are invariant by a birational map. When f is a Halphen or Jonquières twist, we prove that this degree is bounded by a function of $\mathrm{deg}\, f$. We derive corollaries on the structure of conjugacy classes, and their properties with respect to the Zariski topology of $\mathrm{Bir}(\mathbb{P}^2_\mathbf{k})$.

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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