Cosets, voltages, and derived embeddings

An ordinary voltage graph embedding in a surface encodes a certain kind of highly symmetric covering space of that surface. Given an ordinary voltage graph embedding of a graph G in a surface with voltage group A and a connected subgraph H of G, we define special subgroups of A that depend on H and show how cosets of these groups in A can be used to find topological information concerning the derived embedding without constructing the whole covering space. Our strongest theorems treat the case that H is a cycle and the fiber over H is a disjoint union of cycles with annular neighborhoods, in which case we are able to deduce specific symmetry properties of the derived embeddings. We give infinite families of examples that demonstrate the usefulness of our results.