Artin-Schreier-Witt Theory for Stacky Curves

Abstract

We extend our previous classification of stacky curves in positive characteristic using higher ramification data and Artin-Schreier-Witt theory. The main new technical tool introduced is the Artin-Schreier-Witt root stack, a generalization of root stacks to the wildly ramified setting. We then apply our wild Riemann-Hurwitz theorem for stacks to compute the canonical rings of some wild stacky curves.

26 pages; condensed background material, added Subsection 5.1 extending main theorem to cyclic-by-tame automorphisms