Diquark Bose–Einstein condensation and nuclear matter Original Research Article.

We study a possible transition between symmetric nuclear matter and the diquark Bose–Einstein condensate (BEC) matter at zero temperature. We find that chiral restoration transition is first order and coincides with deconfinement. We investigate various possible coexistence patterns which may emerge from the first order deconfinement phase transition by assuming different values for the critical deconfinement chemical potential. If deconfinement takes place at higher chemical potential, there exists a mixed phase of nuclear and chirally restored diquark BEC matter. This coexistence region extends over a large density region for a bigger diquark BEC or a weaker diquark–diquark interaction. For model parameters with heavy diquark in vacuum, phase transition to diquark matter becomes of second-order. We also show that in the case of precocious deconfinement, droplets of nucleons and droplets of chirally restored Bose–Einstein condensed diquarks coexist surrounded by non-trivial vacuum. We show that a early deconfinement and a weak repulsive diquark–diquark interaction soften the equation of state. We propose a scenario in which nuclear matter saturates due to the formation of the diquark BEC and deconfinement phenomena. In this picture, instead of repulsive vector-meson exchange the compressibility of the equation of state is related to a repulsive diquark–diquark interaction. In general, we emphasize the importance of a diquark BEC phase at rather low density before quark BCS-pairing transition.