Absolutely continuous invariant measures for expansive diffeomorphisms of the 2-torus

The aim of this paper is to establish an equivalent criterion for certain expansive diffeomorphisms of the 2-torus to admit an invariant Borel probability measure that is absolutely continuous with respect to the Riemannian volume. Our result is closely related to the well known Livsic-Sinai theorem for Anosov diffeomorphisms.