Generic Galois extensions
AUTOR(ES)
Saltman, David J.
RESUMO
We define the notion of a generic Galois extension with group G over a field F. Let R be a communtative ring of the form F[x1,..., xn](1/s) and let S be a Galois extension of R with group G. Then S/R is generic for G over F if the following holds. Assume K/L is a Galois extension of fields with group G and such that L ⊇ F. Then there is an F algebra map f:R → L such that K ≅ S [unk]RL. We construct generic Galois extensions for certain G and F. We show such extensions are related to Noether's problem and the Grunwald-Wang theorem. One consequence is a simple proof of known counter examples to Noether's problem. On the other hand, we have an elementary proof of a chunk of the Grunwald-Wang theorem, and in a more general context. In fact, we have a Grunwald-Wang-type theorem whenever there is a generic extension for a group G over a field F.
