Effect of pair fluctuations on the electronic properties of the negative Hubbard model

Based on the fact that high-{Tc} superconductors exhibit strong fluctuations, we have allowed the presence of pair fluctuations in the framework of the T-matrix formalism using the 2-D negative Hubbard model for temperatures above and below {Tc}. Our equations are fully self-consistent. For T {ge} {Tc} the electronic properties change drastically with respect to BCS treatment, namely, there is a pseudogap around the chemical potential in the density of states, and the spectral function, A(k,{omega}), vs. {omega} exhibits a double peak structure which is related to the appearance of this pseudogap. For T {le} {Tc}, we have generalized the formalism in order to include the order parameter.