scholarly journals Anisotropic neutron stars with hyperons: implication of the recent nuclear matter data and observations of neutron stars

2020 ◽  
Vol 80 (8) ◽  
Author(s):  
A. Rahmansyah ◽  
A. Sulaksono ◽  
A. B. Wahidin ◽  
A. M. Setiawan
Keyword(s):  
Equation Of State ◽  
Neutron Stars ◽  
Mean Field ◽  
Coupling Constants ◽  
Anisotropic Pressure ◽  
Recent Experimental Data ◽  
Observation Data ◽  
Anisotropic Model ◽  
Mean Field Model ◽  
Anisotropic Models

Abstract Motivated by a recent report by Biwas and Bose (Phys Rev D 99:104002, 2019) that the observations of GW170817 to constrain the extent of pressure anisotropy in neutron stars within Bower–Liang anisotropic model, we systematically study the effects of anisotropic pressure on properties of the neutron stars with hyperons. The equation of state is calculated using the relativistic mean-field model with a BSP parameter set to determine nucleonic coupling constants and by using SU(6) and hyperon potential depths to determine hyperonic coupling constants. We investigate three models of anisotropic pressure known in literature namely Bowers and Liang (Astrophys J 88:657, 1974), Horvat et al. (Class Quant Grav 28:025009, 2011), and Cosenza et al. (J Math Phys (NY) 22:118, 1981). The reliability of the equation of state used is checked by comparing the parameters of the corresponding EOS to recent experimental data. The mass–radius, moment of inertia, and tidal deformability results of Bowers–Liang, Horvat et al., and Cosenza et al. anisotropic models are compared to the corresponding recent results extracted from the analysis of some NS observation data. We have found that the radii predicted by anisotropic NS are sensitive to the anisotropic model used and the results obtained by using the model proposed by Horvat et al. with anisotropic free parameter $$\varUpsilon ~\approx -$$Υ≈- 1.15 are relative compatible with all taken constraints.

scholarly journals Effects of symmetry energy on the radius and tidal deformability of neutron stars in the relativistic mean-field model

2020 ◽  
Vol 2020 (4) ◽  
Author(s):  
Jinniu Hu ◽  
Shishao Bao ◽  
Ying Zhang ◽  
Ken’ichiro Nakazato ◽  
Kohsuke Sumiyoshi ◽  
...  
Keyword(s):  
Neutron Stars ◽  
Symmetry Energy ◽  
Binary Star ◽  
Mean Field ◽  
Mass Region ◽  
Saturation Density ◽  
Coupling Constants ◽  
Mean Field Model ◽  
Relativistic Mean Field ◽  
The Family

Abstract The radii and tidal deformabilities of neutron stars are investigated in the framework of the relativistic mean-field (RMF) model with different density-dependent behaviors of symmetry energy. To study the effects of symmetry energy on the properties of neutron stars, $\omega$ meson and $\rho$ meson coupling terms are included in a popular RMF Lagrangian, i.e., the TM1 parameter set, which is adopted for the widely used supernova equation of state (EoS) table. The coupling constants relevant to the vector–isovector meson, $\rho$, are refitted by a fixed symmetry energy at subsaturation density and its slope at saturation density, while other coupling constants remain the same as the original ones in TM1 so as to update the supernova EoS table. The radius and mass of maximum neutron stars are not so sensitive to the symmetry energy in these family TM1 parameterizations. However, the radii in the intermediate-mass region are strongly correlated with the slope of symmetry energy. Furthermore, the dimensionless tidal deformabilities of neutron stars are also calculated within the associated Love number, which is related to the quadrupole deformation of the star in a static external tidal field and can be extracted from the observation of a gravitational wave generated by a binary star merger. We find that its value at $1.4 \mathrm{M}_\odot$ has a linear correlation to the slope of symmetry energy, unlike that previously studied. With the latest constraints of tidal deformabilities from the GW170817 event, the slope of symmetry energy at nuclear saturation density should be smaller than $60$ MeV in the family TM1 parameterizations. This fact supports the usage of a lower symmetry energy slope for the updated supernova EoS, which is applicable to simulations of neutron star mergers. Furthermore, an analogous analysis is also done within the family IUFSU parameter sets. It is found that the correlations between the symmetry energy slope with the radius and tidal deformability at $1.4 \mathrm{M}_\odot$ have very similar linear relations in these RMF models.

scholarly journals Mass correction and deformation of slowly rotating anisotropic neutron stars based on Hartle–Thorne formalism

2021 ◽  
Vol 81 (8) ◽  
Author(s):  
M. L. Pattersons ◽  
A. Sulaksono
Keyword(s):  
Equation Of State ◽  
Neutron Stars ◽  
Strong Field ◽  
Mean Field ◽  
Anisotropic Model ◽  
Relativistic Stars ◽  
Relativistic Mean Field ◽  
Mass Correction ◽  
The One ◽  
The Impact

AbstractDue to their compactness, neutron stars are the best study matter in high density and strong-field gravity. Hartle and Thorne have proposed a good approximation or perturbation procedure within general relativity for slowly rotating relativistic stars by assuming the matter inside the stars is an ideal isotropic fluid. This study extends the analytical Hartle–Thorne formalism for slowly rotating neutron stars, including the possibility that the neutron star pressure can be anisotropic. We study the impact of neutron stars’ anisotropy pressure on mass correction and deformation numerically. For the anisotropic model, we use the Bowers-Liang model. For the equation of state of neutron stars, we use a relativistic mean-field BSP parameter set with the hyperons, and for the crust equation of state, we use the one of Miyatsu et al. We have found that the mass of neutron stars increases but the radius decreases by increasing $$\lambda _{BL}$$ λ BL value. Therefore, the NS compactness increases when $$\lambda _{BL}$$ λ BL becomes larger. This fact leads to a condition in which NS is getting harder to deformed when the $$\lambda _{BL}$$ λ BL increased.

scholarly journals Equation of State of Hot Dense Hyperonic Matter in the Quark-Meson-Coupling (QMC-A) model

2021 ◽  
Author(s):  
J R Stone ◽  
V Dexheimer ◽  
P A M Guichon ◽  
A W Thomas ◽  
S Typel
Keyword(s):  
Equation Of State ◽  
Neutron Stars ◽  
Nuclear Physics ◽  
Density Functional ◽  
Mean Field ◽  
Baryon Number ◽  
Mean Field Model ◽  
Meson Coupling ◽  
New Equation ◽  
Increasing Temperature

Abstract We report a new equation of state (EoS) of cold and hot hyperonic matter constructed in the framework of the quark-meson-coupling (QMC-A) model. The QMC-A EoS yields results compatible with available nuclear physics constraints and astrophysical observations. It covers the range of temperatures from T=0 to 100 MeV, entropies per particle S/A between 0 and 6, lepton fractions from YL=0.0 to 0.6, and baryon number densities nB=0.05-1.2 fm-3. Applications of the QMC-A EoS are made to cold neutron stars (NS) and to hot proto-neutron stars (PNS) in two scenarios, (i) lepton rich matter with trapped neutrinos (PNS-I) and (ii) deleptonized chemically equilibrated matter (PNS-II). We find that the QMC-A model predicts hyperons in amounts growing with increasing temperature and density, thus suggesting not only their presence in PNS but also, most likely, in NS merger remnants. The nucleon-hyperon phase transition is studied through the adiabatic index and the speed of sound cs. We observe that the lowering of (cs/c)2 to and below the conformal limit of 1/3, is strongly correlated with the onset of hyperons. Rigid rotation of cold and hot stars, their moments of inertia and Kepler frequencies are also explored. The QMC-A model results are compared with two relativistic models, the chiral mean field model (CMF), and the generalized relativistic density functional (GRDF) with DD2 (nucleon-only) and DD2Y-T (full baryon octet) interactions. Similarities and differences are discussed.

scholarly journals The I-Love-Q Relations for Superfluid Neutron Stars

Universe ◽  
2021 ◽  
Vol 7 (4) ◽  
pp. 111
Author(s):  
Cheung-Hei Yeung ◽  
Lap-Ming Lin ◽  
Nils Andersson ◽  
Greg Comer
Keyword(s):  
Fluid Dynamics ◽  
Equation Of State ◽  
Neutron Stars ◽  
Quadrupole Moment ◽  
Fluid Model ◽  
Normal Component ◽  
Approximate Equation ◽  
Mean Field Model ◽  
Polytropic Model ◽  
Two Fluid

The I-Love-Q relations are approximate equation-of-state independent relations that connect the moment of inertia, the spin-induced quadrupole moment, and the tidal deformability of neutron stars. In this paper, we study the I-Love-Q relations for superfluid neutron stars for a general relativistic two-fluid model: one fluid being the neutron superfluid and the other a conglomerate of all charged components. We study to what extent the two-fluid dynamics might affect the robustness of the I-Love-Q relations by using a simple two-component polytropic model and a relativistic mean field model with entrainment for the equation-of-state. Our results depend crucially on the spin ratio Ωn/Ωp between the angular velocities of the neutron superfluid and the normal component. We find that the I-Love-Q relations can still be satisfied to high accuracy for superfluid neutron stars as long as the two fluids are nearly co-rotating Ωn/Ωp≈1. However, the deviations from the I-Love-Q relations increase as the spin ratio deviates from unity. In particular, the deviation of the Q-Love relation can be as large as O(10%) if Ωn/Ωp differ from unity by a few tens of percent. As Ωn/Ωp≈1 is expected for realistic neutron stars, our results suggest that the two-fluid dynamics should not affect the accuracy of any gravitational waveform models for neutron star binaries that employ the relation to connect the spin-induced quadrupole moment and the tidal deformability.

scholarly journals Nuclear equation of state and neutron star cooling

2017 ◽  
Vol 26 (04) ◽  
pp. 1750015 ◽  
Author(s):  
Yeunhwan Lim ◽  
Chang Ho Hyun ◽  
Chang-Hwan Lee
Keyword(s):  
Neutron Star ◽  
Equation Of State ◽  
Neutron Stars ◽  
Nuclear Matter ◽  
Thermal Evolution ◽  
Observation Data ◽  
Nuclear Equation Of State ◽  
The Core ◽  
Dense Nuclear Matter ◽  
Nuclear Models

In this paper, we investigate the cooling of neutron stars with relativistic and nonrelativistic models of dense nuclear matter. We focus on the effects of uncertainties originated from the nuclear models, the composition of elements in the envelope region, and the formation of superfluidity in the core and the crust of neutron stars. Discovery of [Formula: see text] neutron stars PSR J1614−2230 and PSR J0343[Formula: see text]0432 has triggered the revival of stiff nuclear equation of state at high densities. In the meantime, observation of a neutron star in Cassiopeia A for more than 10 years has provided us with very accurate data for the thermal evolution of neutron stars. Both mass and temperature of neutron stars depend critically on the equation of state of nuclear matter, so we first search for nuclear models that satisfy the constraints from mass and temperature simultaneously within a reasonable range. With selected models, we explore the effects of element composition in the envelope region, and the existence of superfluidity in the core and the crust of neutron stars. Due to uncertainty in the composition of particles in the envelope region, we obtain a range of cooling curves that can cover substantial region of observation data.

scholarly journals Constraining bag constant for hybrid neutron stars

2020 ◽  
Vol 29 (07) ◽  
pp. 2050044
Author(s):  
Ishfaq A. Rather ◽  
Ankit Kumar ◽  
H. C. Das ◽  
M. Imran ◽  
A. A. Usmani ◽  
...  
Keyword(s):  
Neutron Stars ◽  
Mean Field ◽  
Effective Field ◽  
Mean Field Model ◽  
Relativistic Mean Field ◽  
Hadron Phase ◽  
Neutron Star Mass ◽  
Mit Bag Model ◽  
Quark Phase ◽  
Bag Constant

We study the star matter properties for Hybrid equation of state (EoS) by varying the bag constant. We use the effective field theory motivated relativistic mean field model (E-RMF) for hadron phase with recently reported FSUGarnet, G3 and IOPB-I parameter sets. The results of NL3 and NL3[Formula: see text] sets are also shown for comparison. The simple MIT bag model is applied for the quark phase to construct the hybrid EoS. The hybrid neutron star mass and radius are calculated by varying with [Formula: see text] to constrain the [Formula: see text] values. It is found that [Formula: see text]–160[Formula: see text]MeV is suitable for explaining the quark matter in neutron stars.

scholarly journals SYMMETRIC GROUND STATES FOR A STATIONARY RELATIVISTIC MEAN-FIELD MODEL FOR NUCLEONS IN THE NON-RELATIVISTIC LIMIT

2012 ◽  
Vol 24 (10) ◽  
pp. 1250025 ◽  
Author(s):  
MARIA J. ESTEBAN ◽  
SIMONA ROTA NODARI
Keyword(s):  
Nuclear Physics ◽  
Field Model ◽  
Mean Field ◽  
Ground States ◽  
Good Choice ◽  
Coupling Constants ◽  
Mean Field Model ◽  
Relativistic Limit ◽  
Relativistic Mean Field ◽  
The One

In this paper, we consider a model for a nucleon interacting with the ω and σ mesons in the atomic nucleus. The model is relativistic, but we study it in the nuclear physics non-relativistic limit, which is of a very different nature from the one of the atomic physics. Ground states with a given angular momentum are shown to exist for a large class of values for the coupling constants and the mesons' masses. Moreover, we show that, for a good choice of parameters, the very striking shapes of mesonic densities inside and outside the nucleus are well described by the solutions of our model.

HYPERON DENSITY DEPENDENCE OF HYPERON-NUCLEON INTERACTIONS IN NEUTRON STARS

2008 ◽  
Vol 17 (09) ◽  
pp. 1720-1728
Author(s):  
L. DANG ◽  
P. YUE ◽  
L. LI ◽  
P. Z. NING
Keyword(s):  
Equation Of State ◽  
Neutron Stars ◽  
Density Dependence ◽  
Mean Field ◽  
Density Dependent ◽  
Effective Potentials ◽  
Relativistic Mean Field ◽  
Nucleon Interactions ◽  
Dependent Factor ◽  
Rmf Model

The hyperon density dependence (YDD) of hyperon-nucleon interactions are studied in the relativistic mean field (RMF) model and their influences on the properties of neutron stars are studied. The extended RMF considered the interior quarks coordinates of hyperon and bring a hyperon density dependent factor, f(ρY), to the meson-hyperon coupling vertexes. The hyperon density dependence of YN interaction affect the properties of neutron stars only after the corresponding hyperon appears. Then, the influences of the density dependence factors are almost ignored at low densities, which are clear at high densities. The compositions and properties of neutron stars are studied with and without the YDD of YN interactions for the different Σ--nucleus effective potentials, (30, 0, -30)MeV. The calculated results indicated that the YDD of YN interaction soften the equation of state of neutron stars at high densities.

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