English

On a variant of the Beckmann--Black problem

Number Theory 2021-11-16 v1

Abstract

Given a field kk and a finite group GG, the Beckmann--Black problem asks whether every Galois field extension F/kF/k with group GG is the specialization at some t0kt_0 \in k of some Galois field extension E/k(T)E/k(T) with group GG and Ek=kE \cap \overline{k} = k. We show that the answer is positive for arbitrary kk and GG, if one waives the requirement that E/k(T)E/k(T) is normal. In fact, our result holds if Gal(F/k){\rm{Gal}}(F/k) is any given subgroup HH of GG and, in the special case H=GH=G, we provide a similar conclusion even if F/kF/k is not normal. We next derive that, given a division ring HH and an automorphism σ\sigma of HH of finite order, all finite groups occur as automorphism groups over the skew field of fractions H(T,σ)H(T, \sigma) of the twisted polynomial ring H[T,σ]H[T, \sigma].

Keywords

Cite

@article{arxiv.2111.07155,
  title  = {On a variant of the Beckmann--Black problem},
  author = {François Legrand},
  journal= {arXiv preprint arXiv:2111.07155},
  year   = {2021}
}
R2 v1 2026-06-24T07:37:21.724Z