Equation of state and sound velocity in hybrid stars with a Dyson–Schwinger quark model

We investigate the equation of state (EOS) and the corresponding sound velocity of the dense matter in hybrid neutron stars. For the hadron matter, the Bruckner–Hartree–Fock (BHF) many-body theory with Bonn-B potential is adopted. For the quark matter, the Dyson–Schwinger quark model is adopted, with the rainbow approximation and the Gaussian type effective interaction for quark–gluon vertex and gluon propagator. The phase transition is considered with both Maxwell condition and Gibbs condition. Then, the sound velocity in the pure hadron phase, pure quark phase and the mixed phase are obtained. The causality requirement [Formula: see text] puts a strong constraint on the EOS from BHF theory. In quark matter, it is found that [Formula: see text] and varies slowly. In the mixed phase with Gibbs condition, the sound velocity varies strongly and nonmonotonically.

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Hybrid compact star in the presence of strong magnetic field

International Journal of Modern Physics E ◽

10.1142/s0218301315500962 ◽

2015 ◽

Vol 24 (12) ◽

pp. 1550096 ◽

Cited By ~ 1

Author(s):

K. Mohanta ◽

N. R. Panda ◽

P. K. Sahu

Keyword(s):

Magnetic Field ◽

Strong Magnetic Field ◽

Quark Matter ◽

Recent Observation ◽

Compact Star ◽

Mixed Phase ◽

Hadronic Matter ◽

Maximum Mass ◽

Surface Magnetic Field ◽

Hadron Phase

Compact neutron stars (NSs) can consist of either hadronic matter or strange quark matter or exotic color superconducting matter. If the stars have a quark core and are surrounded by hadronic matter, they are called hybrid stars (HSs). The HS is a mixture of the hadron and exotic quark phases. Observational results suggest that magnetars are certain NSs having huge surface magnetic field. We calculate equation of states (EOSs) of hadronic and quark matter at high densities in the presence of strong magnetic field and then study the quark–hadron phase having mixed phase in between giving rise to hybrid star. The intermediate mixed phase is constructed based on the Glendenning conjecture. The magnetic field significantly affects the EOS of the matter if the field strength is above [Formula: see text]G. We also calculate HS structure parameters such as the maximum mass, radius, moment of inertia, fundamental period and surface redshift and compare them specially the maximum mass with the recent observation of pulsars PSR 1903+0327 and PSR J1614-2230. The observation restricts a severe constraint on the EOS of matter at extreme conditions.

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Hybrid Stars with Color Superconducting Cores in an Extended FCM Model

Universe ◽

10.3390/universe7100370 ◽

2021 ◽

Vol 7 (10) ◽

pp. 370

Author(s):

Daniela Curin ◽

Ignacio Francisco Ranea-Sandoval ◽

Mauro Mariani ◽

Milva Gabriela Orsaria ◽

Fridolin Weber

Keyword(s):

Equation Of State ◽

Neutron Stars ◽

Quark Matter ◽

Dense Matter ◽

Hadronic Matter ◽

High Mass ◽

Mean Field Approximation ◽

Nuclear Model ◽

Special Focus ◽

Hybrid Stars

We investigate the influence of repulsive vector interactions and color superconductivity on the structure of neutron stars using an extended version of the field correlator method (FCM) for the description of quark matter. The hybrid equation of state is constructed using the Maxwell description, which assumes a sharp hadron-quark phase transition. The equation of state of hadronic matter is computed for a density-dependent relativistic lagrangian treated in the mean-field approximation, with parameters given by the SW4L nuclear model. This model described the interactions among baryons in terms of σ, ω, ρ, σ*, and ϕ mesons. Quark matter is assumed to be in either the CFL or the 2SC+s color superconducting phase. The possibility of sequential (hadron-quark, quark-quark) transitions in ultra-dense matter is investigated. Observed data related to massive pulsars, gravitational-wave events, and NICER are used to constrain the parameters of the extended FCM model. The successful equations of state are used to explore the mass-radius relationship, radii, and tidal deformabilities of hybrid stars. A special focus lies on investigating consequences that slow or fast conversions of quark-hadron matter have on the stability and the mass-radius relationship of hybrid stars. We find that if slow conversion should occur, a new branch of stable massive stars would exist whose members have radii that are up to 1.5 km smaller than those of conventional neutron stars of the same mass. Such objects could be possible candidates for the stellar high-mass object of the GW190425 binary system.

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