New non-arithmetic complex hyperbolic lattices

Abstract

We produce a family of new, non-arithmetic lattices in $${\mathrm{PU}}(2,1)$$ . All previously known examples were commensurable with lattices constructed by Picard, Mostow, and Deligne–Mostow, and fell into nine commensurability classes. Our groups produce five new distinct commensurability classes. Most of the techniques are completely general, and provide efficient geometric and computational tools for constructing fundamental domains for discrete groups acting on the complex hyperbolic plane.