Diquark Bose–Einstein condensation and nuclear matter

Abstract

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 vaccum, 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.

Hybrid stars within a covariant, nonlocal chiral quark model

“…It is a demanding task to develop unified approaches for quark/nuclear matter on the basis of chiral quark models in which nucleons and mesons appear as relativistic bound states of quarks and antiquarks (for first steps in this direction, see Ref. [49,50]). Under conditions of high density and/or temperature these bound states dissociate into continuum correlations (resonances) in quark matter within a Mott transition (see [51] for a model calculation within a nonrelativistic Green functions approach, which has also lead to an early prediction of stable quark matter cores in compact stars [52]).…”

BCS-BEC crossover and phase structure of relativistic systems: A variational approach

“…The scenario that we have in mind is similar to as in Ref. [5], where, as the baryon density is increased, the baryonic matter undergoes a phase transition to diquark BEC phase. The transition from BCS to BEC is most likely to be a crossover similar to their non relativistic counterparts in condensed matter systems like cold fermionic atoms.…”

Nucleons, nuclear matter and quark matter: a unified NJL approach

“…Several recent studies have shown the advantages of using composite nucleons in finite density calculations [1], [2], [3]. For example, in some models the saturation mechanism of the system can be related to how the structure of the nucleon changes with density [4].…”