arXiv subjects

G. B. Alaverdyan

Publications and source records attributed to G. B. Alaverdyan.

14 recordsLinked to original sources

arXiv2022

Properties of Hot Quark Matter with Neutrino Confinement In the NJL Model

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 $T \in [20 ÷100]$ MeV and baryon number densities $n_B \in [0 ÷1.8]$ 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. Keywords: hot quark matter: neutrino confinement: NJL model: equation of state.

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arXiv2022

Quark Matter in the NJL Model with a Vector Interaction and the Structure of Hybrid Stars

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 $G_V$, 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 $P_0$ 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 $P_c$. It is shown that when $G_V$ 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 NASA's Neutron star Interior Composition Explorer (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.

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arXiv2021

Hot Quark Matter with Neutrino Confinement in the Framework of the Local Nambu--Jona-Lasinio SU(3) Model

The thermodynamic characteristics of hot $β$-equilibrium electrically neutral three-flavor quark matter at neutrino confinement are investigated. For the thermodynamic description of such a quark-lepton system, the local SU (3) Nambu--Jona-Lasinio (NJL) model is used, in which also takes into account the 't Hooft interaction, leading to the quark flavor mixing effect. The energy density $\varepsilon$ and pressure $P$ of quark matter are numerically determined for different values of the baryon number density in the range $n_B\in[0.02÷1.8]$ fm$^{-3}$ and temperatures in the range $T\in[0÷100]$ MeV. The results obtained are compared with the results of cold quark matter calculated within the framework of the same model, but under the assumption that all neutrinos have already left the system. The dependence of the contribution of individual quark flavors to the baryon charge of the system at different temperatures is discussed. Both isothermal and adiabatic speeds of sound in hot quark matter are determined depending on the baryon number density.

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arXiv2019

Maximum Mass of Hybrid Stars in the Quark Bag Model

The effect of model parameters in the equation of state for quark matter on the magnitude of the maximum mass of hybrid stars is examined. Quark matter is described in terms of the extended MIT bag model including corrections for one-gluon exchange. For nucleon matter in the range of densities corresponding to the phase transition, a relativistic equation of state is used that is calculated with two particle correlations taken into account based on using the Bonn meson-exchange potential. The Maxwell construction is used to calculate the characteristics of the first order phase transition and it is shown that for a fixed value of the strong interaction constant $α_s$, the baryon concentrations of the coexisting phases grow monotonically as the bag constant B increases. It is shown that for a fixed value of the strong interaction constant $α_s$, the maximum mass of a hybrid star increases as the bag constant $B$ decreases. For a given value of the bag parameter $B$, the maximum mass rises as the strong interaction constant $α_s$ increases. It is shown that the configurations of hybrid stars with maximum masses equal to or exceeding the mass of the currently known most massive pulsar are possible for values of the strong interaction constant $α_s>0.6$ and sufficiently low values of the bag constant.

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arXiv2019

Hybrid Stars in the Framework of the Local Nambu - Jona-Lasinio Model for Quark Matter

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. In our model hybrid stars lie on the same branch as neutron stars, so that a branch with a third family is not formed. 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 $ρ_c\in(1.71 ÷1.73]\cdot 10^{15}$ g/cm$^3$. 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 $M_{max} = 2.05 M_\odot$. The configuration with the maximum mass has a quark core with mass $M_{core} \approx 10^{-3} M_\odot$ and radius $R_{core} \approx 0.6$ km.

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arXiv2012

Deconfinement Phase Transition in Neutron Stars and δ-Meson Field

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 also the scalar-isovector δ-meson field is 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.

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arXiv2012

Energy Release Associated with Quark Phase Transition in Neutron Stars: Comparative Analysis of Maxwell and Glendenning Scenarios

We study the compact stars internal structure and observable characteristics alterations due to the quark deconfinement phase transition. To proceed with, we investigate the properties of isospin-asymmetric nuclear matter in the improved relativistic mean-field (RMF) theory, including a scalar-isovector δ-meson effective field. In order to describe the quark phase, we use the improved version of the MIT bag model, in which the interactions between u, d and s quarks inside the bag are taken into account in the one-gluon exchange approximation. We compute the amount of energy released by the corequake for both cases of deconfinement phase transition scenarios, corresponding to the Maxwellian type ordinary first-order phase transition and the phase transition with formation of a mixed quark-hadron phase (Glendenning scenario).

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arXiv2010

Influence of scalar-isovector delta-meson field on quark phase structure in neutron stars

The deconfinement phase transition from hadronic matter to quark matter in the interior of compact stars is investigated. The hadronic phase is described in the framework of relativistic mean-field (RMF) theory, when also the scalar-isovector delta-meson effective field is taken into account. The MIT bag model for describing a quark phase is used. The changes of the parameters of phase transition caused by the presence of delta-meson field are explored. Finally, alterations in the integral and structural parameters of hybrid stars due to both deconfinement phase transition and inclusion of delta-meson field are discussed.

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arXiv2009

Quark Deconfinement Phase Transition in Neutron Stars

The hadron-quark phase transition in the interior of compact stars is investigated, when the transition proceeds through a mixed phase. The hadronic phase is described in the framework of relativistic mean-field theory, when also the scalar-isovector delta-meson mean-field is taken into account. The changes of the parameters of phase transition caused by the presence of delta-meson field are explored. The results of calculation of structure of the mixed phase (Glendenning construction) are compared with the results of usual first-order phase transition (Maxwell construction).

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arXiv2009

Quark Phase Transition Parameters and $δ$-Meson Field in RMF Theory

The deconfinement phase transition from hadronic matter to quark matter in the interior of compact stars is investigated. The hadronic phase is described in the framework of relativistic mean-field (RMF) theory, when also the scalar- isovector $δ$-meson effective field is taken into account. To describe a quark phase the MIT bag model is used. The changes of the mixed phase threshold parameters caused by the presence of $δ$-meson field are investigated.

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arXiv2009

Relativistic Mean-Field Theory Equation of State of Neutron Star Matter and a Maxwellian Phase Transition to Strange Quark Matter

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 $B\in[60,120]$ $MeV/fm^{3}$ and it is shown that including a $δ$-meson field leads to a reduction in the phase transition pressure $P_{0}$ and in the concentrations $n_{N}$ and $n_{Q}$ at the phase transition point.

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arXiv2004

Neutron Stars with a Quark Core. II.Basic Integral and Structural parameters

A broad sample of computed realistic equations of state of superdense matter with quark phase transition is used to construct a series of models 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 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.

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arXiv2004

Neutron Stars With A Quark Core. I. Equations Of State

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.

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arXiv2004

Low-Mass Quark Stars or Quark White Dwarfs

An equation of state is considered that, in superdense nuclear matter, results in a phase transition of the first kind from the nucleon state to the quark state with a transition parameter Lambda> 3/2. A calculation of the integrated parameters of superdense stars on the basis of this equation of state shows that on the stable branch of the dependence of stellar mass on central pressure (dM/dPc> 0), in the low-mass range, following the formation of a tooth-shaped break (M = 0.08Msun, R = 200 km) due to quark formation, a new local maximum with Mmax = 0.082Msun and R = 1251 km is also formed. The mass and radius of the quark core of such a star turn out to be Mcore = 0.005Msun and Rcore = 1.7 km, respectively. Mass accretion in this model can result in two successive transitions to a neutron star with a quark core, with energy release like supernova outbursts.

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