Rationality problem of three-dimensional monomial group actions
Algebraic Geometry
2011-01-18 v3 Number Theory
Abstract
Let K be a field of characteristic not two and K(x,y,z) the rational function field over K with three variables x,y,z. Let G be a finite group of acting on K(x,y,z) by monomial K-automorphisms. We consider the rationality problem of the fixed field K(x,y,z)G under the action of G, namely whether K(x,y,z)G is rational (that is, purely transcendental) over K or not. We may assume that G is a subgroup of GL(3,Z)andtheproblemisdetermineduptoconjugacyin\mathrm{GL}(3,\mathbb{Z}).Thereare73conjugacyclassesofGin\mathrm{GL}(3,\mathbb{Z}).ByresultsofEndo−Miyata,Voskresenski\i˘,Lenstra,Saltman,Hajja,KangandYamasaki,8conjugacyclassesof2−groupsin\mathrm{GL}(3,\mathbb{Z})havenegativeanswerstotheproblemundercertainmonomialactionsoversomebasefieldK,andthenecessaryandsufficientconditionfortherationalityofK(x,y,z)^GoverKisgiven.Inthispaper,weshowthatthefixedfieldK(x,y,z)^GundermonomialactionofGisrationaloverKexceptforpossiblynegative8casesof2−groupsandunknownonecaseofthealternatinggroupofdegreefour.MoreoverwegiveexplicittranscendentalbasesofthefixedfieldsoverK.Forunknowncase,weobtainanaffirmativesolutiontotheproblemundersomeconditions.Inparticular,weshowthatifKisquadraticallyclosedfieldthenK(x,y,z)^GisrationaloverK$. We also give an application of the result to 4-dimensional linear Noether's problem.
Cite
@article{arxiv.0912.5259,
title = {Rationality problem of three-dimensional monomial group actions},
author = {Akinari Hoshi and Hidetaka Kitayama and Aiichi Yamasaki},
journal= {arXiv preprint arXiv:0912.5259},
year = {2011}
}
Comments
54 pages