Spin fluctuation effects in normal and s-superconducting states in Hubbard systems

We obtain and discuss the self-energy and the renormalized electronic structure of the normal state in strongly correlated electron systems within the pseudogap regime. The effective potentials considered are found from spin fluctuations within a three-dimensional Hubbard single band model. Vertex effects are included and discussed within this formalism. We find that the self-energy tends to violate the Luttinger theorem when the bandwidths are narrowed. We note that when the bands are further narrowed, the corresponding Eliashberg-like equations tend to yield superconductivity. (orig.)