A combinatorial model for the moduli of bordered Riemann surfaces and a compactification

Abstract

We construct a combinatorial moduli space closely related to the KSV-compactification of the moduli space of bordered marked Riemann surfaces. The open part arises from symmetric metric ribbon graphs. The compactification is obtained by considering sequences of noncontractible subgraphs. This leads to a partial real blow-up of rational cells that together form a compact orbi-cell space. For genus zero the constructed space gives an orbi-cell decomposition of the corresponding analytic moduli space decorated by real numbers and a compactification of this space. In higher genus the relation is more involved, as we briefly explain. The spaces we construct are of interest in their own right as they are constructed directly from an interesting class of graphs.