Spectral multiplicity of derived functor modules

AbstractLet Γ be a discrete torsion-free subgroup of a semisimple Lie group G such that the volume of ΓG is finite. We obtain a cohomological interpretation (in the sense of Langlands) of the multiplicity in the discrete spectrum of L2(ΓG) of an irreducible unitarizable derived functor module RsqCλ (after Zuckerman) with non-singular infinitesimal character