Generalization of Luttinger's Theorem for Strongly Correlated Electron   Systems
  Analyzing general structure of the Green function of a strongly correlated electron system we have shown that for the regime of strong correlations Luttinger's theorem should be generalized in the following way: the volume of the Fermi surface of the system of noninteracting particles is equal to volume of the Fermi surface of the quasiparticles in the strongly correlated system with account for the spectral weight of these quasiparticles. Hubbard and t-J models analysis in the paramagnetic nonsuperconducting phase shows that the generalized Luttinger's theorem is valid for these models. 
M.M. Korshunov, S.G. Ovchinnikov