Modified MIT Bag Models—part II: QCD phase diagram and hot quark stars

Abstract

In the present work we use the modified versions of the MIT bag model, on which both a vector field and a self-interacting term are introduced, to obtain hot quark matter and to investigate the QCD phase diagram. We first analyze two-flavored quark matter constrained to both the freeze-out and the liquid-gas phase transition at the hadronic phase. Later, three-flavored quark matter subject to β equilibrium and charge neutrality is used to compute quark star macroscopic properties, which are confronted with recent observational massive and canonical star radius results. Finally, a comparison with QCD phase diagrams obtained from the Nambu-Jona-Lasinio model is performed.

A Neutron Star Is Born

“…After all the discussion on the radii of NS constrained with the help of gravitational wave observation and neutron skin thickness experimental results presented in Section 4.2 and on the uncertainty of these values, I just would like to add one comment: contrary to what is obtained for a family of hadronic stars (maximum mass stars are generally associated with a smaller radii than their canonical star counterparts), a family of quark stars may produce canonical stars with radii that can be approximately the same as the maximum mass star radii, depending on the model used [145], and this feature could accommodate the recent NICER detections for J0030+0451 and J0740+6620. This modified MIT bag model has also been used to investigate the finite temperature systems and to obtain the QCD phase diagram in [5] with the help of a temperature dependent bag B(T), as discussed in the Introduction of the paper. Some of the possible phase diagrams are shown in Figure 23.…”

“…However, it is very important to have in mind the model extrapolations that may be necessary when one moves from the nuclei region shown in Figure 1 to the neutron star (NS) region. A simple treatment of the relation between these two regions and the construction of the QCD phase transition line can be seen in [5]. Figure 1.…”

Hypermassive quark cores

“…The way to obtain the EoS in the original Bag model is well discussed in the ref. [9,10,32]. The free parameter B is not completely arbitrary.…”

“…[7,8], and explore two variations thereof, with a vector channel and with the vector channel altogether with the Dirac sea contribution, as introduced in ref. [9,10].…”

A Bayesian analysis of the properties of hybrid stars with the NJL model

“…In the absence of a satisfactory and controlled computation of the EoS from first-principle QCD with quark and gluonic degrees of freedom [10,11], a large number of phenomenological approaches has been proposed, such as bag models, the quark-meson coupling model and Nambu-Jona-Lasinio (NJL) models [12][13][14][15][16][17][18][19][20][21][22], all dependent on different and largely unconstrained parameters. To appreciate the model dependence of the predictions, it is therefore very important to perform studies where the parameter space is largely studied, at least in the framework of a specific effective approach [23][24][25].…”