Hurwitz monodromy and full number fields

Abstract

We give conditions for the monodromy group of a Hurwitz space over the configuration space of branch points to be the full alternating or symmetric group on the degree. Specializing the resulting coverings suggests the existence of many number fields with surprisingly little ramification-for example, the existence of infinitely many Am or Sm number fields unramified away from {2; 3; 5}.