In the present work we have developed a large-N expansion for the t − J model based on the path integral formulation for Hubbard-operators. Our large-N expansion formulation contains diagrammatic rules, in which the propagators and vertex are written in term of Hubbard operators. Using our large-N formulation we have calculated, for J = 0, the renormalized O(1/N ) boson propagator. We also have calculated the spin-spin and charge-charge correlation functions to leading order 1/N . We have compared our diagram technique and results with the existing ones in the literature.

Using a recently developed perturbative approach, which considers Hubbard operators as fundamental excitations, we have performed electronic self-energy and spectral function calculations for the t − J model on the square lattice. We have found that the spectral functions along the Fermi surface are isotropic, even close to the critical doping where the d-density wave phase takes place. Fermi liquid behavior with scattering rate ∼ ω 2 and a finite quasiparticle weight Z was obtained. Z decreases with decreasing doping taking low values for low doping. Results are compared with other ones, analytical and numerical like slave-boson and Lanczos diagonalization finding agreement. We discuss our results in the light of recent ARP ES experiments in cuprates.