Feedback effects and the self-consistent Thouless criterion of the attractive Hubbard model

We propose a fully microscopic theory of the anomalous normal state of the attractive Hubbard model in the low-density limit that accounts for propaga tor renormalization. Our analytical conclusions regarding the thermodynamic instabilities contained in the self-consistent equations associated with t his formulation have been verified by our comprehensive numerical study of the same equations. The resulting theory is found to contain no transitions at non-zero temperatures for all finite lattices, and we have confirmed, u sing our numerical studies, that this behaviour persists in the thermodynam ic limit for low-dimensional systems. (C) 2001 Elsevier Science B.V. All ri ghts reserved.