English

Good reduction of three-point Galois covers

Algebraic Geometry 2017-10-10 v3 Number Theory

Abstract

Michel Raynaud gave a criterion for a three-point G-cover f : Y \rightarrow X = P^1, defined over a p-adic field K, to have good reduction. In particular, if the order of a p-Sylow subgroup of G is p, and the number of conjugacy classes of elements of order p is greater than the absolute ramification index e of K, then f has potentially good reduction. We give a different proof of this criterion, which extends to the case where G has an arbitrarily large cyclic p-Sylow subgroup, answering a question of Raynaud. We then use the criterion to give a family of examples of three-point covers with good reduction to characteristic p and arbitrarily large p-Sylow subgroups.

Keywords

Cite

@article{arxiv.1208.3909,
  title  = {Good reduction of three-point Galois covers},
  author = {Andrew Obus},
  journal= {arXiv preprint arXiv:1208.3909},
  year   = {2017}
}

Comments

Minor revisions, to appear in Algebraic Geometry. 16 pages