Hybrid stars with the color dielectric and the MIT bag models

Abstract

We study the hadron-quark phase transition in the interior of neutron stars (NS). For the hadronic sector, we use a microscopic equation of state (EOS) involving nucleons and hyperons derived within the Brueckner-Bethe-Goldstone many-body theory, with realistic two-body and three-body forces. For the description of quark matter, we employ both the MIT bag model with a density dependent bag constant, and the color dielectric model. We calculate the structure of NS interiors with the EOS comprising both phases, and we find that the NS maximum masses are never larger than 1.7 solar masses, no matter the model chosen for describing the pure quark phase.

The hadron-quark phase transition in neutron stars

“…One of these constraints is the phenomenological observation that in heavy ion collisions at intermediate energies (10 MeV/A E/A 200 MeV/A) no evidence for a transition to a quark-gluon plasma has been found up to about 3 times the saturation density ρ 0 . We have taken this constraint in due consideration, and used an extended MIT bag model [ 12] (including the possibility of a density dependent bag "constant") and the color dielectric model [ 13], both compatible with this condition [ 14]. For completeness, we have also used the Nambu-Jona-Lasinio model [ 15].…”

Hybrid stars with the Dyson-Schwinger quark model

“…At present, the best one can do is to compare the predictions of different quark models and to estimate the uncertainty of the results for the NS matter as well as for the NS structure and mass. Continuing a set of previous investigations using different quark models [11][12][13][14][15], we employ in this paper the Dyson-Schwinger model (DSM) for QM [16][17][18][19] in combination with a definite baryonic EOS, which has been developed within the Brueckner-Hartree-Fock (BHF) many-body approach of nuclear matter, comprising nucleons and also hyperons. Confrontation with previous calculations shall also be discussed.…”

Neutron Star Structure with Hyperons and Quarks

“…4 (black curves). The most striking effect of the inclusion of quark matter is the increase of the maximum mass relative to the hyperon star, now reaching about 1.5 M for the MIT models with a bag constant B = 100 MeV/fm −3 or with B(ρ), about 1.6 M for the more sophisticated color dielectric model (CDM) [17,22], and about 1.8 M in a recent O(α 2 s ) calculation [18].…”

“…This surprising result is due to the strong softening of the baryonic EOS when including hyperons as additional degrees of freedom, and one does not expect substantial changes when introducing refinements of the theoretical framework, such as hyperon-hyperon potentials, hyperonic TBF [14], relativistic corrections, etc.. The only remaining possibility to reach larger maximum masses appears the transition to another phase of dense (quark) matter inside the star [15][16][17][18].…”

“…In order to overcome these restrictions of the model, one can introduce an empirical density-dependent bag parameter B(ρ), and this approach was followed in Refs. [15][16][17]. This allows one to lower the value of B at large density, providing a stiffer QM EOS and increasing the value of the maximum mass, while at the same time still fulfilling the condition of no phase transition below ρ ≈ 3ρ 0 in symmetric nuclear matter.…”