New York Journal of Mathematics
Volume 23 (2017) 133-164


Tyrone Ghaswala and Rebecca R. Winarski

The liftable mapping class group of balanced superelliptic covers

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Published: January 26, 2017
Keywords: Mapping class groups, branched covers, cyclic covers, spheres, abelianization, symmetric mapping class group
Subject: Primary: 20F38; secondary: 20F34

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. A general superelliptic cover 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.


The second author would like to thank Doug Park's NSERC Discovery Grant for support to visit University of Waterloo.

Author information

Tyrone Ghaswala:
Department of Pure Mathematics, University of Waterloo, Waterloo, ON, N2L 3G1, Canada

Rebecca R. Winarski:
Department of Mathematical sciences, University of Wisconsin-Milwaukee, Milwaukee, WI 53211-3029, USA