Logarithmic Hurwitz Spaces in Mixed and Positive Characteristic with Wild Ramification

Abstract

We introduce new logarithmic Hurwitz spaces ${\mathcal{L}\mathcal{H}}_A^{{\mathbb{Z}}_{(p)}}$ and ${\mathcal{L}\mathcal{H}}_{A,\Xi }^{{\mathbb{F}}_p}$ over ${\mathbb{Z}}_{(p)}$ and ${\mathbb{F}}_p$ respectively that in the mixed characteristic case can be considered as a compactification of the admissible cover stack parametrizing ramified covers of curves in characteristic $0$ of degree $p$ and in the equicharacteristic case compactify the space of separable maps between smooth curves of degree $p$. These Hurwitz spaces will carry a logarithmic structure and to emphasize that they are informative, we prove that in some first cases our Hurwitz spaces are log smooth. To achieve this, we introduce various Moduli spaces that parametrize Artin-Schreier covers and the locus of zeroes and poles of certain differential forms, show their smoothness and compute their dimension.

36 pages, comments welcome!