Nuclear Theory·nucl-th

Wednesday·September 14, 2022

8 papers—5 primary·3 cross-listed

01
Massive relativistic compact stars from SU(3) symmetric quark models
Han Rui Fu (Southwest U.)🇨🇳 · Jia Jie Li (Southwest U.)🇨🇳 · Armen Sedrakian (FIAS and Wroclaw U.)🇩🇪 · Fridolin Weber (San Diego State U. and San Diego, CASS)🇺🇸
We construct a set of hyperonic equations of state (EoS) by assuming SU(3) symmetry within the baryon octet and by using a covariant density functional (CDF) theory approach. The low-density regions of our EoS are constrained by terrestrial experiments, while the high-density regime is modeled by systematically varying the nuclear matter skewness coefficient $Q_{sat}$ and the symmetry energy slope $L_{sym}$ . The sensitivity of the EoS predictions is explored in terms of $z$ parameter of the SU(3) symmetric model that modifies the meson-hyperon coupling constants away from their SU(6) symmetric values. Our results show that model EoS based on our approach can support static Tolman-Oppenheimer-Volkof (TOV) masses in the range $2.3$ - $2.5 M_{⊙}$ in the large- $Q_{sat}$ and small- $z$ regime, however, such stars contain only a trace amount of hyperons compared to SU(6) models. We also construct uniformly rotating Keplerian configurations for our model EoS for which the masses of stellar sequences may reach up to $3.0 M_{⊙}$ . These results are used to explore the systematic dependence of the ratio of maximum masses of rotating and static stars, the lower bound on the rotational frequency of the models that will allow secondary masses in the gravitational waves events to be compact stars with $M_{2} ≲ 3.0 M_{⊙}$ and the strangeness fraction on the model parameters. We conclude that very massive stellar models can be, in principle, constructed within the SU(3) symmetric model, however, they are nucleonic-like as their strangeness fraction drops below 3\%.
nucl-thastro-ph.HEPLB(2022)·16 citations
02
Stability of spherical nuclei in the inner crust of neutron stars
Nikita A. Zemlyakov · Andrey I. Chugunov
Neutron stars are the densest objects in the Universe. In this paper we consider so-called inner crust - the layer, where neutron-excess nuclei are immersed into degenerate gas of electrons and sea of quasi-free neutrons. It was generally believed that spherical nuclei become unstable with respect to quadrupole deformations at high densities and here we consider this instability. Within perturbative approach we show that spherical nuclei with equilibrium number density are, in fact, stable with respect to infinitesimal quadrupole deformation. This is due to background of degenerate electrons and associated electrostatic potential which maintain stability of spherical nuclei. However, if the number of atomic nuclei per unit volume is much less than the equilibrium value, instability can arise. To avoid confusion we stress that our results are limited to infinitesimal deformations and do not guaranty strict thermodynamic stability of spherical nuclei. In particular, they does not exclude that substantially non-spherical nuclei (so-called pasta phase) represent thermodynamic equilibrium state of the densest layers of neutron star crust. Rather our results points that spherical nuclei can be metastable even if they are not energetically favourable and the timescale of transformation of spherical nuclei to the pasta phases should be estimated subsequently.
nucl-thastro-ph.HEParticles(2022)·6 citations
03
Kinetics of the chiral phase transition in a quark-meson $σ$ model
H. van Hees🇩🇪 · A. Meistrenko🇩🇪 · C. Greiner🇩🇪
Using the two-particle irreducible (2PI) $Φ$ -functional formalism for self-consistent approximations of a linear- $σ$ model for quarks and mesons in and out of equilibrium, the build-up of fluctuations of net-baryon number during the time evolution of an expanding fireball is studied within a kinetic theory for the order parameter ( $σ$ field) and quark distribution functions. Initializing the system with purely Gaussian fluctuations a fourth-order cumulant is temporarily built up due to the evolution of the $σ$ -field. This is counterbalanced, however, by the dissipative evolution due to collisions between quarks, anti-quarks, mesons, and the mean field, depending on the speed of the fireball expansion.
nucl-thActa Phys.Polon.Supp.(2023)·0 citations
04
Magnetic-Field Induced Deformation in Hybrid Stars
Ishfaq A. Rather🇵🇹 · Asloob A. Rather🇮🇳 · V. Dexheimer🇺🇸 · Ilídio Lopes🇵🇹 · A. A. Usmani🇮🇳 · S. K. Patra🇮🇳
The effects of strong magnetic fields on the deconfinement phase transition expected to take place in the interior of massive neutron stars are studied in detail for the first time. For hadronic matter, the very general density-dependent relativistic mean-field (DD-RMF) model is employed, while the simple, but effective vector-enhanced bag model (vBag) model is used to study quark matter. Magnetic-field effects are incorporated into the matter equation of state and in the general-relativity solutions, which also satisfy Maxwell's equations. We find that for large values of magnetic dipole moment, the maximum mass, canonical mass radius, and dimensionless tidal deformability obtained for stars using spherically symmetric Tolman-Oppenheimer-Volkoff (TOV) equations and axisymmetric solutions attained through the LORENE library differ considerably. The deviations depend on the stiffness of the equation of state and on the star mass being analyzed. This points to the fact that, unlike what was assumed previously in the literature, magnetic field thresholds for the approximation of isotropic stars and the acceptable use of TOV equations depend on the matter composition and interactions.
nucl-thastro-ph.HEApJ(2023)·18 citations
05
Polytropic fits of modern and unified equations of state
Lami Suleiman🇵🇱 · Morgane Fortin🇵🇱 · Julian-Leszek Zdunik🇵🇱 · Constanca Providencia🇵🇹
Equations of state for a cold neutron star's interior are presented in three-column tables that relate the baryonic density, the energy density, and the pressure. A few analytical expressions for those tables have been established these past two decades, as a convenient way to present a large number of nuclear models for neutron star matter. Some of those analytical representations are based on nonunified equations of state, in the sense that the high and the low density part of the star are not computed with the same nuclear model. Fits of equations of state based on a piecewise polytropic representation are revised by using unified tables of equations of state, that is to say models which have been calculated consistently for the core and the crust. A set of 52 unified equations of state is chosen. Each one is divided in seven polytropes via an adaptive segmentation, and two parameters per polytrope are fitted to the tabulated equation of state. The total mass, radius, tidal deformability and moment of inertia of neutron stars are modelled from the fits and compared with the quantities calculated from the original tables to ensure the accuracy of the fits on macroscopic parameters. We provide the polytropes parameters for 15 nucleonic relativistic mean field models, seven hyperonic relativistic mean field models, five hybrid relativistic mean-field models, 24 nucleonic Skyrme models, and one ab initio model. The fit error on the macroscopic parameters of neutron stars is small and well within the estimated measurement accuracy from current and next generation telescopes.
nucl-thastro-ph.HEastro-ph.SRPRC(2022)·16 citations

Affiliations

first authorsco-authorsvia INSPIRE

Massive relativistic compact stars from SU(3) symmetric quark models

Stability of spherical nuclei in the inner crust of neutron stars

Kinetics of the chiral phase transition in a quark-meson σ model

Magnetic-Field Induced Deformation in Hybrid Stars

Polytropic fits of modern and unified equations of state

Affiliations

Kinetics of the chiral phase transition in a quark-meson $σ$ model