ONE-ELECTRON SPECTRAL FUNCTIONS OF THE ATTRACTIVE HUBBARD-MODEL FOR INTERMEDIATE COUPLING

We calculate the one-electron spectral function of the attractive (neg ative-U) Hubbard model. We work in the intermediate-coupling and low-d ensity regime and obtain the self-energy in an approximate analytical form. The excitation spectrum is found to consist of three branches. T he results are obtained in a framework based on the self-consistent T- matrix approximation, which is compatible with the Mermin-Wagner theor em.