Transcendental Galois Theory and Noether's Problem

TL;DR

This paper explores Noether's problem on rationality using transcendental Galois theory, providing new cases and a generalization of Swan's counter-example, advancing understanding of invariant fields under finite group actions.

Contribution

It develops a general theory connecting Noether's problem with transcendental Galois theory and introduces new specific cases and a broader counter-example.

Findings

New cases of rationality for invariant fields identified

A generalization of Swan's counter-example provided

Enhanced understanding of Galois actions on transcendental extensions

Abstract

In 1918, Noether published a paper where she studied such a problem, now called Noether's problem on rationality: Let $L=K\left( t_{1},t_{2},\cdots ,t_{n}\right) $ be a purely transcendental extension over a field $K$ and $G$ a finite subgroup acting transitively on $t_{1},t_{2},\cdots ,t_{n}$ in an evident manner. Is it true that the invariant subfield $L^{G}$ of $L$ under $% G$ is still purely transcendental over $K$? The problem has been open in general except for minor particular cases. In this paper we will attempt to understand a general theory for Noether's problem on rationality by transcendental Galois theory. Then new particular cases will be obtained. We will also give a generalization for the remarkable counter-example given by Swan in 1969.