Large normal extension of Hilbertian fields
type: Item
instance of: scholarly article
title: Large normal extension of Hilbertian fields
zbMATH Open document ID: 0873.12001
DOI: 10.1007/PL00004298
author: Moshe Jarden
published in: Mathematische Zeitschrift
publication date: 1997-07-03T00:00:00Z
review text: Let \(G(K)\) denote the absolute Galois group of a field \(K\). For \(\sigma \in G(K)^e\) let \(K_s[\sigma]\) be the largest Galois extension of \(K\) which is contained in the fix field \(K_s(\sigma)\) of \(\sigma\). The author shows that for a countable separably Hilbertian field \(K\), for almost all \(\sigma\in G(K)^e\) the field \(K_s[\sigma]\) has these properties: (1) \(K_s[\sigma]\) is PAC (pseudo algebraically closed) (Every non-empty absolutely irreducible variety defined over \(K_s[\sigma]\) has a \(K_s[\sigma]\)-rational point). (2) \(K_s[\sigma]\) is \(\omega\)-free (that means its absolute Galois group is a free profinite group on countably many generators. Hence \(G(K_s[\sigma])\simeq\widehat F_\omega)\). By a result of Roquette, \(K_s [\sigma]\) is separably Hilbertian for these \(\sigma\in G(K)^e\). Being PAC follows from a recent result of K. Neumann. Since for almost all \(\sigma\in G(K)^e\) the Galois group of \(K_s [\sigma]\) is a closed normal subgroup of \(\widetilde F_\omega\), we can apply a result of Melnikov. It states that \(N=G(K_s [\sigma])\) and \(\widehat F_\omega\) are isomorphic if \(N\) has certain quotients. Sections 3 and 4 contain some group theoretic applications and some consequences for decidability.
reviewed by: Martin Epkenhans
Mathematics Subject Classification ID: 12E25
Mathematics Subject Classification ID: 12F99
Mathematics Subject Classification ID: 12L05
zbMATH DE Number: 1028166
zbMATH Keywords: pseudo algebraically closed field
zbMATH Keywords: rational point
zbMATH Keywords: absolute Galois group
zbMATH Keywords: countable separably Hilbertian field
zbMATH Keywords: decidability
MaRDI profile type: Publication
full work available at URL: pl00004298
OpenAlex ID: W2084114773
description: scientific article; zbMATH DE number 1028166