Dynamical mean-field theory for pairing and spin gap in the attractive Hubbard model

We solve the attractive Hubbard model for arbitrary interaction strengths within dynamical mean-field theory. We compute the transition temperature for superconductivity and analyze electron pairing in the normal phase. The normal state is a Fermi liquid at weak coupling and a non-Fermi liquid state with a spin gap at strong coupling. Away from half-filling, the quasi-particle weight vanishes discontinuously at the transition between the two normal states.