Multiple condensed phases in attractively interacting Bose systems

We investigate a Bose gas with finite-range interaction using a scheme to eliminate unphysical repeated collisions in the T-matrix approximation. In this way the corrected T-matrix becomes suitable to calculate properties below the critical temperature. For attractive interaction, the Evans-Rashid transition occurs from the quasi-ideal Bose gas to the BCS-like phase with a gaped dispersion. The gap decreases with increasing density and vanishes at a critical density where the single-particle dispersion becomes linear for small momenta indicating Bose-Einstein condensation.