# On a variant of the Beckmann--Black problem

Abstract : Given a field $k$ and a finite group $G$, the Beckmann--Black problem asks whether every Galois field extension $F/k$ with group $G$ is the specialization at some $t_0 \in k$ of some Galois field extension $E/k(T)$ with group $G$ and $E \cap \overline{k} = k$. We show that the answer is positive for arbitrary $k$ and $G$, if one waives the requirement that $E/k(T)$ is normal. In fact, our result holds if ${\rm{Gal}}(F/k)$ is any given subgroup $H$ of $G$ and, in the special case $H=G$, we provide a similar conclusion even if $F/k$ is not normal. We next derive that, given a division ring $H$ and an automorphism $\sigma$ of $H$ of finite order, all finite groups occur as automorphism groups over the skew field of fractions $H(T, \sigma)$ of the twisted polynomial ring $H[T, \sigma]$.
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Preprints, Working Papers, ...

https://hal-normandie-univ.archives-ouvertes.fr/hal-03430214
Contributor : François Legrand Connect in order to contact the contributor
Submitted on : Tuesday, November 16, 2021 - 10:16:34 AM
Last modification on : Friday, November 19, 2021 - 3:49:02 AM

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### Identifiers

• HAL Id : hal-03430214, version 1
• ARXIV : 2111.07155

### Citation

François Legrand. On a variant of the Beckmann--Black problem. 2021. ⟨hal-03430214⟩

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