A POLYTROPIC APPROACH TO NEUTRON STARS

2010 ◽  
Vol 19 (08n10) ◽  
pp. 1569-1574 ◽  
Author(s):  
L. FERRARI ◽  
P. C. R. ROSSI ◽  
M. MALHEIRO
Keyword(s):  
Neutron Stars ◽  
Sound Velocity ◽  
Equations Of State ◽  
Mass Density ◽  
Mean Field ◽  
Hadronic Matter ◽  
Relativistic Mean Field ◽  
Baryonic Density ◽  
Neutron Star Mass ◽  
Mean Field Equation

We analyze here whether polytropic equations of state can be a good approximation for neutron stars. Dividing the matter in the star interior in different regions that can be well-reproduced by different polytropics and imposing the continuity of the pressure among the regions, we obtain the corresponding neutron star mass–radius diagram. A comparison with the results obtained with the polytropic approximation and the exact relativistic mean-field equation of state (EoS) is shown for two compositions of the hadronic matter. We conclude that with more than one polytropic EoS, it is possible to obtain a good fit to neutron stars only if the pressure is written as a power-law in the energy density (or mass density) and not in the baryonic density (the usual polytropic). We also found a correlation between the sound velocity at the star center and its mass. The sound velocity at the interface between the polytropic regions shows a small discontinuity that is greater for the hadronic matter including hyperons.

FINITE TEMPERATURE EQUATIONS OF STATE FOR MIXED STARS

2004 ◽  
Vol 13 (07) ◽  
pp. 1249-1253
Author(s):  
DÉBORA P. MENEZES ◽  
C. PROVIDÊNCIA
Keyword(s):  
Field Theory ◽  
Neutron Stars ◽  
Quark Matter ◽  
Finite Temperature ◽  
Equations Of State ◽  
Mean Field Theory ◽  
Mean Field ◽  
Relativistic Mean Field Theory ◽  
Relativistic Mean Field

We investigate the properties of mixed stars formed by hadronic and quark matter in β-equilibrium described by appropriate equations of state (EOS) in the framework of relativistic mean-field theory. The calculations were performed for T=0 and for finite temperatures and also for fixed entropies with and without neutrino trapping in order to describe neutron and proto-neutron stars. The star properties are discussed. Maximum allowed masses for proto-neutron stars are much larger when neutrino trapping is imposed.

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 Constraints on Microscopic and Phenomenological Equations of State of Dense Matter from GW170817

Universe ◽  
2019 ◽  
Vol 5 (10) ◽  
pp. 204 ◽  
Author(s):  
Domenico Logoteta ◽  
Ignazio Bombaci
Keyword(s):  
Neutron Star ◽  
Neutron Stars ◽  
Equations Of State ◽  
Mean Field ◽  
Dense Matter ◽  
Neutron Star Matter ◽  
Field Approach ◽  
Relativistic Mean Field ◽  
Three Body ◽  
Good Agreement

We discuss the constraints on the equation of state (EOS) of neutron star matter obtained by the data analysis of the neutron star-neutron star merger in the event GW170807. To this scope, we consider two recent microscopic EOS models computed starting from two-body and three-body nuclear interactions derived using chiral perturbation theory. For comparison, we also use three representative phenomenological EOS models derived within the relativistic mean field approach. For each model, we determine the β -stable EOS and then the corresponding neutron star structure by solving the equations of hydrostatic equilibrium in general relativity. In addition, we calculate the tidal deformability parameters for the two neutron stars and discuss the results of our calculations in connection with the constraints obtained from the gravitational wave signal in GW170817. We find that the tidal deformabilities and radii for the binary’s component neutron stars in GW170817, calculated using a recent microscopic EOS model proposed by the present authors, are in very good agreement with those derived by gravitational waves data.

EFFECTS OF Δ-BARYON INTERACTION STRENGTH ON NEUTRON STARS PROPERTIES

2007 ◽  
Vol 16 (02n03) ◽  
pp. 175-183 ◽  
Author(s):  
J. C. T. DE OLIVEIRA ◽  
S. B. DUARTE ◽  
H. RODRIGUES ◽  
M. CHIAPPARINI ◽  
M. KYOTOKU
Keyword(s):  
Equation Of State ◽  
Neutron Stars ◽  
Mean Field Theory ◽  
Mean Field ◽  
Interaction Strength ◽  
Hadronic Matter ◽  
Resonance Neutron ◽  
Baryon Interaction ◽  
Relativistic Mean Field ◽  
Central Regions

We investigate the effect of Δ-resonance interaction strength on the equation of state of asymmetric hadronic matter and neutron stars structure. We discuss Δ-matter formation at high densities in the context of a relativistic mean field theory. We show that the attractive nature of the Δ-baryon interaction can induce a phase transition accompanying Δ-matter formation, at values of densities presumably existing in central regions of neutron stars. The possibility of a rich Δ-resonance neutron star is presented using the proposed equation of state.

SIGNATURES OF ISOVECTOR COMPONENTS OF THE SCALAR σ-MESON IN NEUTRON STARS

2004 ◽  
Vol 13 (07) ◽  
pp. 1255-1259 ◽  
Author(s):  
EDUARDO LÜTZ ◽  
MOISÉS RAZEIRA ◽  
CÉSAR A. Z. VASCONCELLOS ◽  
MANFRED DILLIG
Keyword(s):  
Neutron Star ◽  
Scalar Field ◽  
Neutron Stars ◽  
Mean Field ◽  
Hadronic Matter ◽  
Field Approach ◽  
Relativistic Mean Field ◽  
Intermediate States

Based on non-crossed, crossed and correlated ππ exchanges with irreducible N, Δ intermediate states, we predict an isovector component for the σ meson. We study dense hadronic matter in a generalized relativistic mean field approach with nonlinear self-couplings of the I=0,1 components of the scalar field and compare its predictions for neutron star properties with results from different models found in the literature.

scholarly journals Properties of rotating neutron star in density-dependent relativistic mean-field models

2020 ◽  
pp. 2150001
Author(s):  
Rashid Riahi ◽  
Seyed Zafarollah Kalantari
Keyword(s):  
Neutron Star ◽  
Neutron Stars ◽  
Quadrupole Moment ◽  
Stability Region ◽  
Equations Of State ◽  
Mean Field ◽  
Low Frequency ◽  
Density Dependent ◽  
Relativistic Mean Field ◽  
Limit Value

Equilibrium sequences were developed for rotating neutron stars in the relativistic mean-field interaction framework using four density-dependent equations of state (EOSs) for the neutron star matter. These sequences were constructed for the observed rotation frequencies of 25, 317, 346, 716 and 1122[Formula: see text]Hz. The bounds of sequences, the secular axisymmetric instability, static and Keplerian sequences were calculated in each model to determine the stability region. The gravitational mass, quadrupole moment, polar, forward and backward redshifts, and Kerr parameter were calculated according to this stability region, and the allowable range of these quantities was then determined for each model. According to the results, DDF and DD-ME[Formula: see text] were unable to properly describe the low-frequency neutron stars, PSR J0348+432, PSR J1614-2230 and PSR J0740+6620 rotate at a frequency of 25, 317 and 346[Formula: see text]Hz, respectively. On the other hand, all the selected EOSs properly described the rotation of PSR J1748-244ad and PSR J1739-285 at a frequency of 716 and 1122[Formula: see text]Hz, respectively. The mass of these stars was, therefore, in the range of [Formula: see text] and [Formula: see text], respectively. The polar, forward and backward redshifts, and the quadrupole moment were calculated in all the selected rotating frequencies and the Keplerian sequence. The results were consistent with observations. Confirming the mass of [Formula: see text] for EXO 0748-676, our result, [Formula: see text], will be close to the observed value, and the EOSs used in this study properly describe this star. Interestingly, the extremum of Kerr parameter, polar, forward and backward redshifts in all models reached constant values of, [Formula: see text], [Formula: see text], [Formula: see text] and [Formula: see text], respectively. These behaviors of redshifts and Kerr parameter are approximately independent of EOS. The observed behaviors must evaluate by other EOSs to find universal relations for these quantities. Also, a limit value was found for each of these parameters. In this case where these parameters are greater than the limit value, the star can rotate at a frequency equal to or greater than [Formula: see text][Formula: see text]Hz.

scholarly journals Deconfinement of nonstrange hadronic matter with nucleons and Δ baryons to quark matter in neutron stars

2019 ◽  
Vol 28 (02) ◽  
pp. 1950040 ◽  
Author(s):  
Debashree Sen ◽  
T. K. Jha
Keyword(s):  
Neutron Star ◽  
Neutron Stars ◽  
Quark Matter ◽  
Mean Field ◽  
Static Condition ◽  
Hadronic Matter ◽  
Chiral Model ◽  
Vector Coupling ◽  
Binary Neutron Star ◽  
Relativistic Mean Field

We explore the possibility of formation of [Formula: see text] baryons (1232[Formula: see text]MeV) in neutron star matter in an effective chiral model within the relativistic mean-field framework. With variation in delta-meson couplings, consistent with the constraints imposed on them, the resulting equation-of-state (EoS) is obtained and the neutron star properties are calculated for static and spherical configuration. Within the framework of our model, the critical densities of formation of [Formula: see text] and the properties of neutron stars (NS) are found to be very sensitive to the iso-vector coupling compared to the scalar or vector couplings. We revisit the [Formula: see text] puzzle and look for the possibility of phase transition from nonstrange hadronic matter (including nucleons and [Formula: see text]) to deconfined quark matter, based on QCD theories. The resultant hybrid star configurations satisfy the observational constraints on mass from the most massive pulsars PSR J1614-2230 and PSR J0348+0432 in static condition obtained with the general hydrostatic equilibrium based on GTR. Our radius estimates are well within the limits imposed from observational analysis of QLMBXs. The obtained values of [Formula: see text] are in agreement with the recent bounds specified from the observation of gravitational wave (GW170817) from binary neutron star merger. The constraint on baryonic mass from the study of binary system PSR J0737-3039 is also satisfied with our hybrid EoS.

scholarly journals PROPERTIES OF MAGNETIZED QUARK-HYBRID STARS

2011 ◽  
Vol 20 (supp02) ◽  
pp. 25-28
Author(s):  
MILVA ORSARIA ◽  
IGNACIO F. RANEA-SANDOVAL ◽  
H. VUCETICH ◽  
FRIDOLIN WEBER
Keyword(s):  
Magnetic Field ◽  
Field Equation ◽  
Equation Of State ◽  
Uniform Magnetic Field ◽  
Mean Field ◽  
Hadronic Matter ◽  
Relativistic Mean Field ◽  
Standard Neutron ◽  
Hybrid Stars ◽  
Mean Field Equation

The structure of a magnetized quark-hybrid stars (QHS) is modeled using a standard relativistic mean-field equation of state (EoS) for the description of hadronic matter. For quark matter we consider a bag model EoS which is modified perturbatively to account for the presence of a uniform magnetic field. The mass-radius (M-R) relationship, gravitational redshift and rotational Kepler periods of such stars are compared with those of standard neutron stars (NS).

NONLINEAR σ, δ DERIVATIVE SELF-COUPLINGS IN A RMFT FOR NEUTRON STARS

2004 ◽  
Vol 13 (07) ◽  
pp. 1485-1491 ◽  
Author(s):  
SÉRGIO S. ROCHA ◽  
MOISÉS RAZEIRA ◽  
CÉSAR A. Z. VASCONCELLOS ◽  
MANFRED DILLIG
Keyword(s):  
Neutron Stars ◽  
Nuclear Matter ◽  
Mean Field ◽  
Hadronic Matter ◽  
Field Approach ◽  
Relativistic Mean Field ◽  
Global Properties ◽  
Substantial Modification ◽  
Nonlinear Couplings

We study dense hadronic matter in a generalized relativistic mean field approach which contains nonlinear couplings of the σ, ω, ϱ, δ fields and compare its predictions for properties of neutron stars with the corresponding results from different models found in the literature. Our predictions indicate a substantial modification in static global properties of nuclear matter and neutron stars with the inclusion of the δ meson into the formalism.

scholarly journals Phases of Hadron-Quark Matter in (Proto) Neutron Stars

Universe ◽  
2019 ◽  
Vol 5 (7) ◽  
pp. 169 ◽  
Author(s):  
Fridolin Weber ◽  
Delaney Farrell ◽  
William M. Spinella ◽  
Germán Malfatti ◽  
Milva G. Orsaria ◽  
...  
Keyword(s):  
Neutron Stars ◽  
Quark Matter ◽  
Mean Field Theory ◽  
Mean Field ◽  
Hadronic Matter ◽  
Relativistic Mean Field ◽  
Quark Flavor ◽  
Flavor Mixing ◽  
Non Local ◽  
Quark Deconfinement

In the first part of this paper, we investigate the possible existence of a structured hadron-quark mixed phase in the cores of neutron stars. This phase, referred to as the hadron-quark pasta phase, consists of spherical blob, rod, and slab rare phase geometries. Particular emphasis is given to modeling the size of this phase in rotating neutron stars. We use the relativistic mean-field theory to model hadronic matter and the non-local three-flavor Nambu–Jona-Lasinio model to describe quark matter. Based on these models, the hadron-quark pasta phase exists only in very massive neutron stars, whose rotational frequencies are less than around 300 Hz. All other stars are not dense enough to trigger quark deconfinement in their cores. Part two of the paper deals with the quark-hadron composition of hot (proto) neutron star matter. To this end we use a local three-flavor Polyakov–Nambu–Jona-Lasinio model which includes the ’t Hooft (quark flavor mixing) term. It is found that this term leads to non-negligible changes in the particle composition of (proto) neutron stars made of hadron-quark matter.

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