  We present a study of the attractive Hubbard model based on the dynamical
mean field theory (DMFT) combined with the numerical renormalization group
(NRG). For this study the NRG method is extended to deal with self-consistent
solutions of effective impurity models with superconducting symmetry breaking.
We give details of this extension and validate our calculations with DMFT
results with antiferromagnetic ordering. We also present results for static and
integrated quantities for different filling factors in the crossover from weak
(BCS) to strong coupling (BEC) superfluidity. We study the evolution of the
single-particle spectra throughout the crossover regime. Although the DMFT does
not include the interaction of the fermions with the Goldstone mode, we find
strong deviations from the mean-field theory in the intermediate and strong
coupling (BEC) regimes. In particular, we show that low-energy charge
fluctuations induce a transfer of spectral weight from the Bogoliubov
quasiparticles to a higher-energy incoherent hump.
