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The properties of isospin-asymmetric cold nuclear matter are studied in terms of the relativistic mean-field theory in which, besides the fields of σ, ω, and ρ mesons, and the isovector, Lorentz-scalar field of the δ-meson is also taken into account. The properties of purely nucleonic np matter are studied as a function of the baryon density nB and the asymmetry parameter α, as well as the properties of electrically neutral β-equilibrium npe μ matter as a function of the baryon density nB. For different values of nB and a, such characteristics of np matter as the energy per baryon, the specific energy owing to isospin asymmetry, the effective proton and neutron masses, and the specific binding energy, are determined. It is shown that the energy owing to the asymmetry for a fixed value of α is a monotonically increasing function of the baryon density nB. For npem matter, the effective proton and neutron masses M p e f f , M n e f f , the specific binding energy Ebind, the symmetry energy Esym, the quantitative fraction of protons Yp = np/nB are studied, as well as the average meson fields σ ~ , ω ~ , δ ~ , and ρ ~ as functions of the baryon density nB. [ABSTRACT FROM AUTHOR]

The effect of neutrino oscillations on the thermodynamic characteristics of three-flavor hot quark matter in β-equilibrium that is opaque for neutrinos is examined in terms of the local SU(3) Nambu-Jona-Lasinio (NJL) model which also accounts for the 't Hooft interaction that leads to quark flavor mixing. The thermodynamic characteristics of quark matter are determined for two temperatures, T = 60 and 100 MeV, with neutrino oscillations taken into account. These results are compared with those obtained without taking neutrino oscillations into account. The calculations show that during cooling of quark matter that is opaque to neutrinos, the energy released per unit of baryon charge is 150 ÷ 350 MeV. [ABSTRACT FROM AUTHOR]

The properties of hadron-quark hybrid stars are studied when the quark phase is described in terms of a local SU(3) Nambu-Jona-Lasinio (NJL) model taking into account the contribution of the vector and axial-vector interaction between the quarks, and the hadronic phase, in the relativistic mean field (RMF) model. For different values of the vector coupling constant GV, the equations of state of the quark matter are calculated and the parameters of the hadron-quark phase transition are determined under the assumption that the phase transition takes place in accordance with Maxwell's construction. It is shown that for a larger vector coupling constant, the equation of state of the quark matter will be "stiffer" and the coexistence pressure P0 of the phases will be greater. Using the resulting hybrid equations of state, the TOV equations are integrated numerically and the mass and radius of the compact star are determined for different values of the central pressure Pc. It is shown that when GV is larger, the maximum mass of the compact star will be larger and thereby, the radius of the configuration with maximum mass will be smaller. Questions of the stability of hybrid stars are also discussed. It is shown that in terms of the model examined here, for all values of the vector coupling constant, a hybrid star with an infinitely small quark core is stable. These results are compared with recent measurements of the mass and radius of the pulsars PSR J0030+0451 and PSR J0740+6620, carried out at the International Space Station with the NICER X-ray telescope. A comparison of the theoretical results with observational data does not exclude the possibility of quark deconfinement in the interiors of compact stars. [ABSTRACT FROM AUTHOR]

The thermodynamic characteristics of hot β-equilibrium three-flavor quark matter with neutrino confinement are studied in terms of the local SU(3) Nambu-Jona-Lasinio (NJL) model, which also accounts for the 't Hooft interaction which leads to mixing of quark flavors. For different temperatures T ∈ [20 ÷100] MeV and baryon number densities nB ∈ [0 ÷ 1.8] fm-3 the constituent quark masses, quark condensates, and relative contributions of individual types of particles to the pressure and chemical potentials of the constituent particles are determined. In order to determine the role of neutrinos in the hot quark matter, the pressures and energies in states with and without neutrinos are compared. [ABSTRACT FROM AUTHOR]

The thermodynamic characteristics of hot β-equilibrium, electrically neutral, three-flavor quark matter with neutrino confinement are studied. This kind of quark-lepton system is described thermodynamically using a local SU(3) Nambu - Jona-Lasinio (NJL) model that includes the 't Hooft interaction, leading to a mixing effect for the quark flavors. The energy density e and pressure P of the quark matter are determined numerically for baryon number densities in the range of nB ϵ [0.02 ÷ 1.8] fm-3 and temperatures of T ϵ [0 ÷ 100]MeV. These results are compared with the results for cold quark matter calculated in the same model framework but under the assumption that all neutrinos have already left the system. The dependence of the contribution of the individual quark flavors to the baryonic charge of the system for different temperatures is discussed. The isothermal and adiabatic speeds of sound in hot quark matter are both calculated as functions of the baryonic number density. [ABSTRACT FROM AUTHOR]

The integral parameters of neutron stars are studied taking into account the hadron-quark phase transition, which leads to the formation of a core of quark matter in the central part of a star. The quark matter is described using the local Nambu-Jona-Lasinio (NJL) model. The thermodynamic characteristics of the hadron matter are calculated in the framework of an extended version of the relativistic mean field (RMF) model that includes the contribution of the scalar-isovector δ -meson effective field. A Maxwell construction is used to determine the parameters of the phase transition. It is shown that for the equation of state examined here, stable hybrid stars correspond to a narrow range of values for the central density ρc ∈ (1.71÷1.73]·1015 g/cm3. In our model hybrid stars lie on the same branch as neutron stars, so that a branch with a third family is not formed. The maximum mass of a stable hybrid star is found to be _ Mmax = 2.05M⨀. The configuration with the maximum mass has a quark core with mass Mcore ≈ 10-3 M⨀ and radius Rcore ≈ 0.6 km. [ABSTRACT FROM AUTHOR]

The Maxwell and Glendenning construction scenarios of deconfinement phase transition in neutron star matter are investigated. The hadronic phase is described within the relativistic mean-field (RMF) theory, if the scalar-isovector δ-meson field is also taken into account. The strange quark phase is described in the frame of MIT bag model, including the effect of perturbative one-gluon exchange interactions. The influence of the δ-meson field on the deconfinement phase transition boundary characteristics is discussed. [ABSTRACT FROM AUTHOR]

The equation of state of neutron star matter is examined in terms of the relativistic mean-field theory, including a scalar-isovector δ-meson effective field. The constants of the theory are determined numerically so that the empirically known characteristics of symmetric nuclear matter are reproduced at the saturation density. The thermodynamic characteristics of both asymmetric nucleonic matter and β-equilibrium hadron-electron npe-plasmas are studied. Assuming that the transition to strange quark matter is an ordinary first-order phase transition described by Maxwell's rule, a detailed study is made of the variations in the parameters of the phase transition owing to the presence of a δ-meson field. The quark phase is described using an improved version of the bag model, in which interactions between quarks are accounted for in a one-gluon exchange approximation. The characteristics of the phase transition are determined for various values of the bag parameter within the range B ∈ [60,120]MeV/fm3 and it is shown that including a δ-meson field leads to a reduction in the phase transition pressure P0 and in the concentrations n N and n Q at the phase transition point. [ABSTRACT FROM AUTHOR]

A broad sample of computed realistic equations of state of superdense matter with a quark phase transition is used to construct a series of models of neutron stars with a strange quark core. The integral characteristics of the stellar configurations are obtained: gravitational mass, rest mass, radius, relativistic moment of inertia, and red shift from the star’s surface, as well as the mass and radius of the quark core within the allowable range of values for the central pressure. The parameters of some of the characteristic configurations of the calculated series are also given and these are studied in detail. It is found that a new additional region of stability for neutron stars with strange quark cores may exist for some models of the equation of state. [ABSTRACT FROM AUTHOR]

An extensive set of realistic equations of state for superdense matter with a quark phase transition is derived on the basis of the three equations of state for neutron matter and the eight variants of strange quark-gluon plasmas in the MIT quark bag model. The characteristics of the phase transitions are described and the calculated equations of state with a density jump are studied in detail. [ABSTRACT FROM AUTHOR]

We consider an equation of state that leads to a first-order phase transition from the nucleon state to the quark state with a transition parameter λ > 3/2 (λ = ρ[sub Q]/(ρ[sub N] + P[sub 0]/c²)) in superdense nuclear matter. Our calculations of integrated parameters for superdense stars using this equation of state show that on the stable branch of the dependence of stellar mass on central pressure (dM/dP[sub c] > 0) in the range of low masses, a new local maximum with M[sub max] = 0.082[sub ⊙] and R = 1251 km appears after the formation of a toothlike kink (M = 0.08M[sub ⊙], R = 205 km) attributable to quark production. For such a star, the mass and radius of the quark core are M[sub core] = 0.005M[sub ⊙] and R[sub core] = 1.73 km, respectively. In the model under consideration, mass accretion can result in two successive transitions to a quark-core neutron star with energy release similar to a supernova explosion: initially, a low-mass star with a quark core is formed; the subsequent accretion leads to configurations with a radius of ∼ 1000 km; and, finally, the second catastrophic restructuring gives rise to a star with a radius of ∼ 100 km. [ABSTRACT FROM AUTHOR]