The liftable mapping class group of balanced superelliptic covers

Abstract

The hyperelliptic mapping class group has been studied in various contexts within topology and algebraic geometry. What makes this study tractable is that there is a surjective map from the hyperelliptic mapping class group to a mapping class group of a punctured sphere. The more general family of superelliptic mapping class groups does not, in general, surject on to a mapping class group of a punctured sphere, but on to a finite index subgroup. We call this finite index subgroup the liftable mapping class group. In order to initiate the generalization of results on the hyperelliptic mapping class group to the broader family of superelliptic mapping class groups, we study an intermediate family called the balanced superelliptic mapping class group. We compute the index of the liftable mapping class group in the full mapping class group of the sphere and show that the liftable mapping class group is independent of the degree of the cover. We also build a presentation for the liftable mapping class group, compute its abelianization, and show that the balanced superelliptic mapping class group has finite abelianization. Although our calculations focus on the subfamily of balanced superelliptic mapping class groups, our techniques can be extended to any superelliptic mapping class group, even those not within the balanced family.