(2+1) gravity for higher genus in the polygon model

We construct explicitly a (12g − 12)-dimensional space \cal P of unconstrained and independent initial data for 't Hooft's polygon model of (2+1) gravity for vacuum spacetimes with compact genus-g spacelike slices, for any g ≥ 2. Our method relies on interpreting the boost parameters of the gluing data between flat Minkowskian patches as the lengths of certain geodesic curves of an associated smooth Riemann surface of the same genus. The appearance of an initial big bang or a final big crunch singularity (but never both) is verified for all configurations. Points in \cal P correspond to spacetimes which admit a one-polygon tessellation, and we conjecture that \cal P is already the complete physical phase space of the polygon model. Our results open the way for numerical investigations of pure (2+1) gravity.