Attractive boson and the gas-liquid condensation

Gas-liquid condensation (GLC) in the attractive uniform Bose gas is studied by applying the idea of the Yang-Lee zeros to its grand partition function. The followings are proved: (i) When the temperature decreases and the density increases, the GLC occurs prior to the Bose-Einstein condensation (BEC), (ii) an explosive growth of the Bose-statistical coherence to a macroscopic scale occurs simultaneously with the GLC, which are triggered by bosons with a zero momentum, and (iii) the GLC in the Bose.-as is not only a condensation in coordinate space, but also in momentum space. On the basis of these results, a comparative study of the BEC and the GLC is developed. Further, we discuss its implication to the trapped atomic gas.