2010/06/26 by Feng-Wen An, An, Feng-Wen
Mathematics · #14G25 #FOS: Mathematics #Number Theory (math.NT) #Primary 11G35 #Secondary 14F35 #math.NT #msc:11G35 #msc:14F35 #msc:14G25
paper · pdf · doi:10.48550/arxiv.1006.5143
13 pages
arxiv created 2010/06/26 · arxiv updated 2010/06/29
In this paper we will give a scheme-theoretic discussion on the unramified extensions of an arithmetic function field in several variables. The notion of unramified discussed here is parallel to that in algebraic number theory and for the case of classical varieties, coincides with that in Lang's theory of unramified class fields of a function field in several variables. It is twofold for us to introduce the notion of unramified. One is for the computation of the étale fundamental group of an arithmetic scheme; the other is for an ideal-theoretic theory of unramified class fields over an arithmetic function field in several variables. Fortunately, in the paper we will also have operations on unramified extensions such as base changes, composites, subfields, transitivity, etc. It will be proved that a purely transcendental extension over the rational field has a trivial unramified extension. As an application, it will be seen that the affine scheme of a ring over the ring of integers in several variables has a trivial étale fundamental group.