Galois groups of function fields with prescribed
ramification
Riemann surfaces; ramification; differential forms; sheaf
cohomology; Riemann-Roch; Riemann-Hurwitz; function fields; Galois
theory of valuations; profinite groups; Galois groups.
he purpose of this dissertation is to understand the phenomenon of
ramification.
On one hand, we investigate what happens in the more classical and
‘geometrical’ case of Riemann surfaces, exploring their basic
properties, what it means for a holomorphic function between surfaces
to have ramification and branch points, the definitions of divisors
and of the genus of a compact Riemann surface X and the theorems of
Riemann-Roch and Riemann-Hurwitz. We aim to exemplify these concepts
via a few examples and calculations.
On the other hand, we talk about the concept of function fields and,
using the language of valuations, places and valuation rings, we
define for function fields concepts which are, in some sense, very
similar to the ones we study in the Riemann surfaces case. It is the
intention to highlight the similarity between both cases.
Finally, in the last chapter, we explore how the genus of functions
fields can be used to prove results regarding their Galois groups;
specifically, that the genus and the ramification of certain prime
divisors profoundly influence the structure of these profinite groups.