Triangle groups in the complex hyperbolic plane and special fibers of the momentum map in PU(2,1)

Abstract

In this work, we consider relative character varieties for representations of the 3-punctured sphere group in PU(2,1). We provide necessary and sufficient conditions on the peripheral conjugacy classes, for such a representation to admit a decomposition as products of special elliptic elements. We prove that the representations satisfying these conditions form fibers of the so-called momentum map for PU(2,1). We apply these results to representations of the even subgroup of triangle groups, and describe components of the associated character variety.