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arXiv 1111.5060math.NT
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关于多项式映射的Northcott性质及其它性质

On the Northcott property and other properties related to polynomial mappings

Sara Checcoli, Martin Widmer

摘要:

证明了:若$K/\mathbb{Q}$是有限指数的Galois扩张,且$K^{(d)}$是$K$的所有次至多为$d$的扩张的合成,则$K^{(d)}$具有Bogomolov性质,而$K^{(d)}/\mathbb{Q}$的极大阿贝尔子扩张具有Northcott性质.证明了给定任意有限可解群序列$\{G_m\}_m$,存在具有$\text{Gal}(K_m/\mathbb{Q})=G_m$的Galois扩张序列$\{K_m\}_m$,使得域$K_m$的合成具有Northcott性质.特别是,我们提供的例子与一致有界的地方度,但不包含在$\mathbb{Q}^{(d)}$的Northcott属性字段。我们还讨论了Liardet和Narkiewicz为研究多项式映射而引入的性质所涉及的一些问题。利用Northcott性质的结果和Dvornicich和Zannier的结果,我们很容易推导出Narkiewicz提出的一些开放问题的答案。

英文摘要:

We prove that if $K/\mathbb{Q}$ is a Galois extension of finite exponent and $K^{(d)}$ is the compositum of all extensions of $K$ of degree at most $d$, then $K^{(d)}$ has the Bogomolov property and the maximal abelian subextension of $K^{(d)}/\mathbb{Q}$ has the Northcott property. Moreover, we prove that given any sequence of finite solvable groups $\{G_m\}_m$ there exists a sequence of Galois extensions $\{K_m\}_m$ with $\text{Gal}(K_m/\mathbb{Q})=G_m$ such that the compositum of the fields $K_m$ has the Northcott property. In particular we provide examples of fields with the Northcott property with uniformly bounded local degrees but not contained in $\mathbb{Q}^{(d)}$. We also discuss some problems related to properties introduced by Liardet and Narkiewicz to study polynomial mappings. Using results on the Northcott property and a result by Dvornicich and Zannier we easily deduce answers to some open problems proposed by Narkiewicz.

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