Compact arithmetic quotients of the complex 2-ball and a conjecture of Lang

Abstract

Let X be a compact quotient of the unit ball in ℂ^2 by an arithmetic subgroup Γ of a unitary group defined by an anisotropic hermitian form on a three dimensional vector space over a CM field with signature (2,1) at one archimedean place and (3,0) at the others. We prove that if all the torsion elements of Γ are scalar, then X is Mordellic, meaning that for any number field k containing the field of definition of X, the set X(k) of k-rational points of X is finite. The proof applies and combines certain key results of Faltings with the work of Rogawski and the hyperbolicity of X.