arXiv subjects

A. Sulaksono

Publications and source records attributed to A. Sulaksono.

At least 37 records · Page 2Linked to original sources

arXiv2018

Compactness, masses and radii of compact stars within the Eddington-inspired Born-Infeld theory

We investigate the compactness, masses and radii of realistic neutron stars (NSs) and quark stars (QSs) within the Eddington-inspired Born-Infeld (EiBI) theory of gravity, and the energy conditions of their apparent equation of states (EOSs). We show that the maximum compactness and maximum masses constraints extracted from the recent pulsars masses and radii observations can provide the upper and lower limits of $κ$ value of EiBI theory. By using BSP parameter set of relativistic mean field (RMF) model to describe NS core EOS including hyperons, it can be estimated that $ (2.7 \le κ_g \le 7.9) \times$ $\rm 10^{-2} m^5 kg^{-1} s^{-2}$. If we use confined-isospin-density-dependent-mass (CIDDM) model with additional scalar Coulomb term with QSK046 parameter set to describe QS EOS, we can obtain lesser value i.e., $ (1.6 \le κ_g\le 2.2) \times$ $\rm 10^{-2} m^5 kg^{-1} s^{-2}$. We have also observed that for large $κ$ values, mass-radius relations of NSs and QSs do not exceed causality restrictions because the compactness of NS and QS are saturated after passing certain large critical value. This observation is in agreement with the results obtained in Ref.\cite{Delsate12} for the case of pressure-less stars. We have also found that if $κ$ larger than certain non-zero value, the CIDDM with vector Coulomb model prediction of QS can reach the maximum mass $\gtrsim$ 2 $M_\odot$. We have found also that if the NS or QS EOS becomes stiffer, the upper limit of $κ$ from compactness constraint becomes smaller and lower limit of $κ$ from maximum masses constraint becomes larger. We also observe that the uncertainty of the systematic in canonical mass compact stars radii measurements data can affect the $κ$ range. It is also shown that the non-physical apparent EOS of NSs and QSs can satisfy the energy conditions.

gr-qc↗

arXiv2017

Information-Entropic Method: Stability of Stars and Modified Gravity Theories

We study the stability of non-relativistic polytropic stars within two modified gravity theories i.e., Beyond Horndeski gravity and Eddington inspired Born Infeld theories using the configuration entropy method. We use spatially localized bounded function of energy density as solutions from stellar effective equations to construct the corresponding configuration entropy. We use the same argument as the one used by the authors of Refs. [1,2] that the stars are stable if there is peak in configuration entropy as a function of adiabatic index curve. Specifically, the boundary between stable and unstable regions which corresponds to Chandrasekhar stability bound is indicated from the existence of the maximum peak while the most stable polytropic stars is indicated by minimum peak in the corresponding curve. We have found that the value of critical adiabatic indexes of Chandrasekhar stability bound and the most stable polytropic stars predicted by non-relativistic limit of Beyond Horndeski Gravity and Eddington inspired Born Infeld theories are different to those predicted by general relativity where the corresponding differences depend on the free parameter of both theories.

gr-qc↗

arXiv2017

Neutron stars in the braneworld within the Eddington-inspired Born-Infeld gravity

We propose the disappearance of "the hyperon puzzle" in neutron star (NS) by invoking two new-physics prescriptions: modified gravity theory and braneworld scenario. By assuming that NS lives on a $3$-brane within a $5d$ empty AdS bulk, gravitationally governed by Eddington-inspired Born-Infeld (EiBI) theory, the field equations can be effectively cast into the usual Einstein's with "apparent" anisotropic energy-momentum tensor. Solving the corresponding brane-TOV equations numerically, we study its mass-radius relation. It is known that the appearance of finite brane tension $λ$ reduces the compactness of the star. The compatibility of the braneworld results with observational constraints of NS mass and radius can be restored in our model by varying the EiBI's coupling constant, $κ$. We found that within the astrophysically-accepted range of parameters ($0<κ<6\times10^6\text{m}^2$ and $λ\gg1~ \text{MeV}^4$) the NS can have mass $\sim2.1~ \text{M}_\odot$ and radius $\sim10$ km.

astro-ph.CO↗

arXiv2017

Imprint of Nucleon Radius on the Slowly Rotating Neutron Star Properties

We have studied the effect of free space nucleon radius on the nuclear matter and slowly rotating neutron star properties within a relativistic mean field model with the inclusion of omega-rho mixing nonlinear term. We use the same density dependent radius as in our previous work. However, in the present work we utilize the parameter sets with more proper symmetric nuclear matter (SNM) predictions for a number of different nucleon radii. To this end, the isoscalar parameters in each parameter set and the cutoff parameter $β$ are adjusted by fitting the corresponding SNM properties at sub-saturation density to the prediction of IUFSU parameter set. We have obtained that the assumption of composite nucleons with free space radius $r \le 0.83$ fm is still compatible with the currently acceptable nuclear matter (NM) properties beyond the saturation density. We have also found that the effect of free space nucleon radius could be imprinted in the radius, moment of inertia, and crust properties of the slowly rotating neutron star.

nucl-th↗

arXiv2016

Strong correlations of neutron star radii with the slopes of nuclear matter incompressibility and symmetry energy at saturation

We examine the correlations of neutron star radii with the nuclear matter incompressibility, symmetry energy, and their slopes, which are the key parameters of the equation of state (EoS) of asymmetric nuclear matter. The neutron star radii and the EoS parameters are evaluated using a representative set of 24 Skyrme-type effective forces and 18 relativistic mean field models, and two microscopic calculations, all describing 2$M_\odot$ neutron stars. Unified EoSs for the inner-crust-core region have been built for all the phenomenological models, both relativistic and non-relativistic. Our investigation shows the existence of a strong correlation of the neutron star radii with the linear combination of the slopes of the nuclear matter incompressibility and the symmetry energy coefficients at the saturation density. Such correlations are found to be almost independent of the neutron star mass in the range $0.6\text{-}1.8M_{\odot}$. This correlation can be linked to the empirical relation existing between the star radius and the pressure at a nucleonic density between one and two times saturation density, and the dependence of the pressure on the nuclear matter incompressibility, its slope and the symmetry energy slope. The slopes of the nuclear matter incompressibility and the symmetry energy coefficients as estimated from the finite nuclei data yield the radius of a $1.4M_{\odot}$ neutron star in the range $11.09\text{-}12.86$ km.

nucl-th↗

arXiv2016

Impacts of the tensor couplings of $ω$ and $ρ$ mesons and Coulomb exchange terms on super-heavy nuclei and their relation to symmetry energy

We have studied the effects of tensor coupling of $ω$ and $ρ$ meson terms, Coulomb exchange term in local density approximation and various isoscalar-isovector coupling terms of relativistic mean field model on the properties of nuclear matter, finite nuclei, and super-heavy nuclei. We found that for the same fixed value of symmetry energy $J$ or its slope $L$ the presence of tensor coupling of $ω$ and $ρ$ meson terms and Coulomb exchange term yields thicker neutron skin thickness of $^{208}$Pb. We also found that the roles of tensor coupling of $ω$ and $ρ$ meson terms, Coulomb exchange term in local density approximation and various isoscalar-isovector coupling terms on the bulk properties of finite nuclei varies depending on the corresponding nucleus mass. However, on average, tensor coupling terms play a significant role in predicting the bulk properties of finite nuclei in a quite wide mass range especially in binding energies. We also observed that for some particular nuclei, the corresponding experimental data of binding energies is rather less compatible with the presence of Coulomb exchange term in local density approximation and they tend to disfavor the presence of isoscalar-isovector coupling term with too high $Λ$ value. Furthermore, we have found that these terms influence the detail properties of $^{292}$120 super-heavy nucleus such as binding energies, the magnitude of two nucleon gaps, single particle spectra, neutron densities, neutron skin thicknesses and mean square charge radii. However, the shell closure predictions of $^{208}$Pb and $^{292}$120 nuclei is not affected by the presence of these terms.

nucl-th↗

arXiv2016

Quark Matter at High Density based on Extended Confined-isospin-density-dependent-mass Model

We investigate the effect of the inclusion of relativistic Coulomb terms in a confined-isospin-density-dependent-mass (CIDDM) model of strange quark matter (SQM). We found that if we include Coulomb term in scalar density form, SQM equation of state (EOS) at high densities is stiffer but if we include Coulomb term in vector density form is softer than that of standard CIDDM model. We also investigate systematically the role of each term of the extended CIDDM model. Compared with what was reported in Ref.~\cite {ref:isospin}, we found the stiffness of SQM EOS is controlled by the interplay among the the oscillator harmonic, isospin asymmetry and Coulomb contributions depending on the parameter's range of these terms. We have found that the absolute stable condition of SQM and the mass of 2 $M_\odot$ pulsars can constrain the parameter of oscillator harmonic $κ_1$ $\approx 0.53$ in the case Coulomb term excluded. If the Coulomb term is included, for the models with their parameters are consistent with SQM absolute stability condition, the $2.0~M_{\odot}$ constraint more prefer the maximum mass prediction of model with scalar Coulomb term than that of model with vector Coulomb term. On contrary, the high densities EOS predicted by model with vector Coulomb is more compatible with recent pQCD result \cite{ref:pressure} than that predicted by model with scalar Coulomb. Furthermore, we also observed the quark composition in a very high density region depends quite sensitively on the kind of Coulomb term used.

nucl-th↗

arXiv2016

Hyperons in neutron stars within Eddington-inspired Born-Infeld theory of gravity

We investigate the mass-radius relation of neutron star (NS) with hyperons inside its core by using the Eddington-inspired Born-Infeld (EiBI) theory of gravity. The equation of state of the star is calculated by using the relativistic mean field model under which the standard SU(6) prescription and hyperons potential depths are used to determine the hyperon coupling constants. We found that, for $4\times 10^{6}~\rm{m^2}~\lesssim~κ\lesssim~6\times 10^{6}~\rm{m^2}$, the corresponding NS mass and radius predicted by the EiBI theory of gravity is compatible with observational constraints of maximum NS mass and radius. The corresponding $κ$ value is also compatible with the $κ$ range predicted by the astrophysical-cosmological constraints. We also found that the parameter $κ$ could control the size and the compactness of a neutron star.

astro-ph.SR↗

arXiv2016

Correlation of the neutron star crust-core properties with the slope of the symmetry energy and the lead skin thickness

The correlations of the crust-core transition density and pressure in neutron stars with the slope of the symmetry energy and the neutron skin thickness are investigated, using different families of relativistic mean field parametrizations with constant couplings and non-linear terms mixing the $σ$, $ω$ and $ρ$-meson fields. It is shown that the modification of the density dependence of the symmetry energy, involving the $σ$ or the $ω$ meson, gives rise to different behaviors: the effect of the $ω$-meson may also be reproduced within non-relativistic phenomenological models, while the effect of the $σ$-meson is essentially relativistic. Depending on the parametrization with $σ-ρ$ or $ω-ρ$ mixing terms, different values of the slope of the symmetry energy at saturation must be considered in order to obtain a neutron matter equation of state compatible with results from chiral effective field theory. This difference leads to different pressures at the crust-core transition density. A linear correlation between the transition density and the symmetry energy slope or the neutron skin thickness of the $^{208}$Pb nucleus is obtained, only when the $ω$-meson is used to describe the density dependence of the symmetry energy. A comparison is made between the crust-core transition properties of neutron stars obtained by three different methods, the Relativistic Random Phase Approximation (RRPA), the Vlasov equation and Thermodynamical method. It is shown that the RRPA and the Vlasov methods predict similar transition densities for $pne$ $β$-equilibrium stellar matter.

nucl-th↗

arXiv2015

Diversities in the properties of neutron stars at a fixed neutron-skin thickness in $^{208}$Pb nucleus

We study the diversities in the properties of the neutron stars arising due to the different choices for the cross-coupling between various mesons which governs the density dependence of the nuclear symmetry energy in the extended relativistic mean-field(RMF) model. For this purpose, we obtain two different families of the extended RMF model corresponding to different non-linear cross-coupling term in the isovector part of the effective Lagrangian density. The lowest order contributions for the $δ$ mesons are also included. The different models within the same family are so obtained that they yield wide variation in the value of neutron-skin thickness in the $^{208}$Pb nucleus. These models are employed to compute the neutron star properties such as, core-crust transition density, radius and red shift at canonical mass ($1.4M_{\odot}$), tidal polarizability parameter, and threshold mass required for the enhanced cooling through direct Urca process. Most of the neutron star properties considered are significantly different(10\%-40\%) for the different families of models at a smaller neutron-skin thickness ($\sim 0.15$ fm) in the $^{208}$Pb nucleus.

nucl-th↗

arXiv2014

Anisotropic pressure and hyperons in neutron stars

We study the effects of anisotropic pressure on properties of the neutron stars with hyperons inside its core within the framework of extended relativistic mean field. It is found that the main effects of anisotropic pressure on neutron star matter is to increase the stiffness of the equation of state, which compensates for the softening of the EOS due to the hyperons. The maximum mass and redshift predictions of anisotropic neutron star with hyperonic core are quite compatible with the result of recent observational constraints if we use the parameter of anisotropic pressure model $h \le 0.8$[1] and $Λ\le -1.15$ [2]. The radius of the corresponding neutron star at $M$=1.4 $M_\odot$ is more than 13 km, while the effect of anisotropic pressure on the minimum mass of neutron star is insignificant. Furthermore, due to the anisotropic pressure in the neutron star, the maximum mass limit of higher than 2.1 $M_\odot$ cannot rule out the presence of hyperons in the neutron star core.

nucl-th↗

arXiv2014

Boson star at finite temperature

By using a simple thermodynamical method we confirm the finding of Chavanis and Harko that stable Bose-Einstein condensate stars can form. However, by using a thermodynamically consistent boson equation of state, we obtain a less massive Bose-Einstein condensate star compared to the one predicted by Chavanis and Harko. We also obtain that the maximum mass of a boson star is insensitive to the change of matter temperature. However, the mass of boson star with relatively large radius depends significantly on the temperature of the boson matter.

astro-ph.SR↗

arXiv2014

Core-crust transition properties of neutron stars within systematically varied extended relativistic mean-field model

The model dependence and the symmetry energy dependence of the core-crust transition properties for the neutron stars are studied using three different families of systematically varied extended relativistic mean field model. Several forces within each of the families are so considered that they yield wide variations in the values of the nuclear symmetry energy $a_{\rm sym}$ and its slope parameter $L$ at the saturation density. The core-crust transition density is calculated using a method based on random-phase-approximation. The core-crust transition density is strongly correlated, in a model independent manner, with the symmetry energy slope parameter evaluated at the saturation density. The pressure at the transition point dose not show any meaningful correlations with the symmetry energy parameters at the saturation density. At best, pressure at the transition point is correlated with the symmetry energy parameters and their linear combination evaluated at the some sub-saturation density. Yet, such correlations might not be model independent. The correlations of core-crust transition properties with the symmetry energy parameter are also studied by varying the symmetry energy within a single model. The pressure at the transition point is correlated once again with the symmetry energy parameter at the sub-saturation density.

nucl-th↗

arXiv2013

Constraining the density dependence of symmetry energy from nuclear masses

Empirically determined values of the nuclear volume and surface symmetry energy coefficients from nuclear masses are expressed in terms of density distributions of nucleons in heavy nuclei in the local density approximation. This is then used to extract the value of the symmetry energy slope parameter $L$. The density distributions in both spherical and well deformed nuclei calculated within microscopic framework with different energy density functionals give $L = 59.0 \pm 13.0$ MeV. Application of the method also helps in a precision determination of the neutron skin thickness of nuclei that are difficult to measure accurately.

nucl-th↗

arXiv2013

Nonidentical protons

We have calculated the proton charge radius by assuming that the real proton radius is not unique and the radii are randomly distributed in a certain range. This is performed by averaging the elastic electron-proton differential cross section over the form factor cut-off. By using a dipole form factor and fitting the middle value of the cut-off to the low $Q^2$ Mainz data, we found the lowest $χ^2/N$ for a cut-off $Λ=0.8203\pm 0.0003$ GeV, which corresponds to a proton charge radius $r_E=0.8333\pm 0.0004$ fm. The result is compatible with the recent precision measurement of the Lamb shift in muonic hydrogen as well as recent calculations using more sophisticated techniques. Our result indicates that the relative variation of the form factor cut-off should be around 21.5%. Based on this result we have investigated effects of the nucleon radius variation on the symmetric nuclear matter (SNM) and the neutron star matter (NSM) by considering the excluded volume effect in our calculation. The mass-radius relation of neutron star is found to be sensitive to this variation. The nucleon effective mass in the SNM as well as the equation of state of both the SNM and the NSM exhibit a similar sensitivity.

nucl-th↗

arXiv2012

Existence of hyperons in the pulsar PSRJ1614-2230

The possibility of existence of hyperons in the recently measured $2M_\odot$ pulsar PSRJ1614-2230 is explored using a diverse set of nuclear equations of state calculated within the relativistic mean-field models. Our results indicate that the nuclear equations of state compatible with heavy-ion data allow the hyperons to exist in the PSRJ1614-2230 only for significantly larger values for the meson-hyperon coupling strengths. The maximum mass configurations for these cases contain sizable hyperon fractions ($\sim 60%$) and yet masquared their counterpart composed of only nucleonic matter.

nucl-th↗

arXiv2012

Optimization of relativistic mean field model for finite nuclei to neutron star matter

We have optimized the parameters of extended relativistic mean-field model using a selected set of global observables which includes binding energies and charge radii for nuclei along several isotopic and isotonic chains and the iso-scalar giant monopole resonance energies for the $^{90}$Zr and $^{208}$Pb nuclei. The model parameters are further constrained by the available informations on the energy per neutron for the dilute neutron matter and bounds on the equations of state of the symmetric and asymmetric nuclear matter at supra-nuclear densities. Two new parameter sets BSP and IUFSU* are obtained, later one being the variant of recently proposed IUFSU parameter set. The BSP parametrization uses the contributions from the quartic order cross-coupling between $ω$ and $σ$ mesons to model the high density behaviour of the equation of state instead of the $ω$ meson self-coupling as in the case of IUFSU* or IUFSU. Our parameter sets yield appreciable improvements in the binding energy systematics and the equation of state for the dilute neutron matter. The importance of the quartic order $ω-σ$ cross coupling term of the extended RMF model, as often ignored, is realized.

nucl-th↗

arXiv2009

Criteria for nonlinear parameters of relativistic mean field models

Based on the properties of the critical and the actual effective masses of sigma and omega mesons, criteria to estimate the values of the isoscalar nonlinear terms of the standard relativistic mean field model that reproduce stable equations of state in respect to particle hole excitation at high densities are derived. The relation between nuclear matter stability and the symmetric nuclear matter properties are shown. The criteria are used to analyze in a more systematic way the high-density longitudinal and transverse instabilities of some parameter sets of relativistic mean field models. The critical role of the vector and vector-scalar nonlinear terms is also discussed quantitatively.

nucl-th↗