Mapping class groups of covers with boundary and braid group embeddings

Abstract

We consider finite-sheeted, regular, possibly branched covering spaces of compact surfaces with boundary and the associated liftable and symmetric mapping class groups. In particular, we classify when either of these subgroups coincides with the entire mapping class group of the surface. As a consequence, we construct infinite families of non-geometric embeddings of the braid group into mapping class groups in the sense of Wajnryb. Indeed, our embeddings map standard braid generators to products of Dehn twists about curves forming chains of arbitrary length. As key tools, we use the Birman-Hilden theorem and the action of the mapping class group on a particular fundamental groupoid of the surface.

arXiv comment34 pages, 13 figures. Changes suggested by the referee have been made, minor typos fixed. To appear in Algebraic & Geometric Topology

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• The Birman-Hilden theory
• Generating the liftable mapping class groups of regular cyclic covers