arXiv subjects

H. C. Das

Publications and source records attributed to H. C. Das.

At least 37 records · Page 2Linked to original sources

arXiv2023

Impacts of dark matter interaction on nuclear and neutron star matter within the relativistic mean-field model

This thesis explores the effects of dark matter (DM) on neutron stars (NSs) using the relativistic mean-field (RMF) model. The effects of DM on NS properties, including the mass-radius relation, the moment of inertia, and tidal deformability, are calculated by varying its fraction. The study found that the EOS becomes softer with increasing DM momentum, and the DM has marginal effects on nuclear matter properties, except for the EOSs and binding energy per particle. The study also calculated the properties of isolated, static, and rotating DM admixed NS and found that the DM has significant effects on both static and rotating NS. We have also observed that a tiny amount of DM can accumulate inside the NS, and more amount of it makes the NS unstable. The study also suggests that the secondary component might be a NS with DM content if the underlying nuclear EOS is sufficiently stiff. The $f$-mode oscillations of the DM admixed hyperon stars are calculated and found that there exist a correlation between canonical $f$-mode frequency and the dimensionless tidal deformability parameter ($Λ_{1.4}$) and we have put a constraint on $f$-mode frequency using GW170817 data. Finally, we have calculated the DM admixed binary NS properties and found that the binary system becomes less deformed and sustains more time in its inspiral phases with the addition of DM. Therefore, we suggest that one can take DM inside the compact objects while modeling the inspiral waveforms for the BNS systems.

nucl-th↗

arXiv2023

Constraining the Surface Curvature of an Anisotropic Neutron Star

The anisotropy of pressure arises due to the various complex phenomena that happen inside the neutron star (NS). In this study, we calculate the degree of anisotropy inside the NS using the scalar pressure anisotropy model. Macroscopic properties such as mass, radius, compactness, redshift, tidal deformability, the moment of inertia, and surface curvature (SC) are computed for the anisotropic NS with the equation of states spanning from relativistic to nonrelativistic cases. The variation of SC as the functions of the above-mentioned quantities are computed by changing the degree of anisotropy. Pressure anisotropy has significant effects on the magnitude of SC. The universal relations between the canonical SC$-Λ$ and SC$-\bar{I}$ are studied. From the GW170817 tidal deformability data constraints on SC are found to be SC$_{1.4}(10^{14}) = 3.44_{-1.0}^{+0.4}, 2.85_{-1.20}^{+0.62}, \ {\rm and} \ 2.52_{-1.02}^{+0.61}$ for $λ_{\rm BL} = 0.0, 1.0$, and $2.0$ respectively.

astro-ph.HE↗

arXiv2023

Magnetised neutron star crust within effective relativistic mean-field model

Even though the crystallize nature of the neutron star crust plays a pivotal role in describing various fascinating astrophysical observations, its microscopic structure is not fully understood in the presence of a colossal magnetic field. In the present work, we study the crustal properties of a neutron star within an effective relativistic mean field framework in the presence of magnetic field strength $\sim 10^{17}$G. We calculate the equilibrium composition of the outer crust by minimizing the Gibbs free energy using the most recent atomic mass evaluations. The magnetic field significantly affects the equation of state (EoS) and the properties of the outer crust, such as neutron drip density, pressure, and melting temperature. For the inner crust, we use the compressible liquid drop model for the first time to study the crustal properties in a magnetic environment. The inner crust properties, such as mass and charge number distribution, isospin asymmetry, cluster density, etc., show typical quantum oscillations (De Haas-van Alphen effect) sensitive to the magnetic field's strength. The density-dependent symmetry energy influences the magnetic inner crust like the field-free case. We study the probable modifications in the pasta structures and it is observed that their mass and thickness changes by $\sim 10-15 \%$ depending upon the magnetic field strength. The fundamental torsional oscillation mode frequency is investigated for the magnetized crust in the context of quasiperiodic oscillations (QPO) in soft gamma repeaters. The magnetic field strengths considered in this work influences only the EoS of outer and shallow regions of the inner crust, which results in no significant change in global neutron star properties. However, the outer crust mass and its moment of inertia increase considerably with increase in magnetic field strength.

astro-ph.HE↗

arXiv2022

$I-$Love$-C$ relation for an anisotropic neutron star

One of the most common assumptions has been made that the pressure inside the star is isotropic in nature. However, the pressure is locally anisotropic in nature which is a more realistic case. In this study, we investigate certain properties of anisotropic neutron stars with the scalar pressure anisotropy model. Different perfect fluid conditions are tested within the star with the relativistic mean-field model equation of states (EOSs). The anisotropic neutron star properties such as mass ($M$), radius ($R$), compactness ($C$), Love number ($k_2$), dimensionless tidal deformability ($Λ$), and the moment of inertia ($I$) are calculated. The magnitude of the quantities as mentioned above increases (decreases) with the positive (negative) value of anisotropy except $k_2$ and $Λ$. The Universal relation $I-$Love$-C$ is calculated with almost 58 EOSs spans from relativistic to non-relativistic cases. We observed that the relations between them get weaker when we include anisotropicity. With the help of the GW170817 tidal deformability limit and radii constraints from different approaches, we find that the anisotropic parameter is less than 1.0 if one uses the BL model. Using the universal relation and the tidal deformability bound given by the GW170817, we put a theoretical limit for the canonical radius, $R_{1.4}=10.74_{-1.36}^{+1.84}$ km, and the moment of inertia, $I_{1.4} = 1.77_{-0.09}^{+0.17}\times10^{45}$ g cm$^2$ with 90\% confidence limit for isotropic stars. Similarly, for anisotropic stars with $λ_{\rm BL}=1.0$, the values are $R_{1.4}=11.74_{-1.54}^{+2.11}$ km, $I_{1.4} = 2.40_{-0.08}^{+0.17} \times10^{45}$ g cm$^2$ respectively.

gr-qc↗

arXiv2022

Pasta properties of the neutron star within effective relativistic mean-field model

We study the properties of pasta structures and their influence on the neutron star observables employing the effective relativistic mean-field (E-RMF) model. The compressible liquid drop model is used to incorporate the finite size effects, considering the possibility of nonspherical structures in the inner crust. The unified equation of states are constructed for several E-RMF parameters to study various properties such as pasta mass and thickness in the neutron star's crust. The majority of the pasta properties are sensitive to the symmetry energy in the subsaturation density region. Using the results from Monte Carlo simulations, we estimate the shear modulus of the crust in the context of quasiperiodic oscillations from soft gamma-ray repeaters and calculate the frequency of fundamental torsional oscillation mode in the inner crust. Global properties of the neutron star such as mass-radius profile, the moment of inertia, crustal mass, crustal thickness, and fractional crustal moment of inertia are worked out. The results are consistent with various observational and theoretical constraints.

nucl-th↗

arXiv2022

Thermal Relaxation of Dark Matter Admixed Neutron Star

Motivated by the various theoretical studies regarding the efficient capturing of dark matter by neutron stars, we explore the possible indirect effects of captured dark matter on the cooling mechanism of a neutron star. The equation of states for different configurations of dark matter admixed star at finite temperature is obtained using the relativistic mean-field formalism with the IOPB-I parameter set. We show that the variation in the dark matter momentum vastly modifies the neutrino emissivity through specific neutrino generating processes of the star. The specific heat and the thermal conductivity of a dark matter admixed star have also been investigated to explore the propagation of cooling waves in the interior of the star. The dependence of theoretical surface temperature cooling curves on the equation of state and chemical composition of the stellar matter has also been discussed along with the observational data of thermal radiation from various sources. We observed that the dark matter admixed canonical stars with $k_{f}^{\rm DM} > 0.04$ comply with the fast cooling scenario. Further, the metric for internal thermal relaxation epoch has also been calculated with different dark matter momentum and we deduced that increment of dark matter segment amplify the cooling and internal relaxation rates of the star.

astro-ph.HE↗

arXiv2022

Systematic study for the surface properties of neutron star

[Background] In our earlier work {\bf [Phys. Rev. C 104, 055804 (2021)]}, we studied the surface properties of a neutron star, assuming it as a huge finite nucleus containing protons, neutrons, electrons, and muons. For the first time, we reported these results of a neutron star for a few representative masses. In the present paper, we give a detailed study of these quantities to draw definite conclusions. [Method]To carry forward our earlier idea, the energy density functional of the momentum space of neutron star matter is converted to the coordinate space in a local density approximation. This functional is again used to derive the neutron star surface properties within the coherent density fluctuation model using the weight function obtained from the density profile of the neutron star using the recently developed G3 and widely used NL3 and IU-FSU parameter sets in the context of relativistic mean-field formalism. [Results] The systematic surface properties of the neutron star, such as incompressibility, symmetry energy, slope parameter, and curvature coefficient, is calculated. The volume and surface components of the total symmetry energy are decomposed with the help of the $κ$ factor obtained from the volume to surface ratio of the symmetry energies in the liquid drop limit of Danielewicz. The magnitude of the computed surface quantities increases with the neutron star's mass. [Conclusion] The incompressibility $K^{\rm star}$, symmetry energy $S^{\rm star}$, slope parameter $L_{\rm sym}^{\rm star}$ and curvature coefficient $K_{\rm sym}^{\rm star}$ of the neutron stars with different mass are analyzed and found to be model dependent. NL3 is the stiffest equation of state endue us with the higher magnitude of surface quantities as compared to the G3 and IU-FSU forces.

nucl-th↗

arXiv2022

Crustal properties of a neutron star within an effective relativistic mean-field model

We use the effective relativistic mean-field (E-RMF) model to study the crustal properties of the neutron star. The unified equations of state (EoS) are constructed using recently developed E-RMF parameter sets, such as FSUGarnet, IOPB-I, and G3. The outer crust composition is determined using the atomic mass evaluation 2020 data [Chinese Physics C {\bf 45}, 030002 (2021)] along with the available Hartree-Fock-Bogoliubov mass models [Phys. Rev. C {\bf 88}, 024308 (2013)] for neutron-rich nuclei. The structure of the inner crust is estimated by performing the compressible liquid drop model calculations using the same E-RMF functional as that for the uniform nuclear matter in the liquid core. Various neutron star properties such as mass-radius ($M-R$) relation, the moment of inertia ($I$), the fractional crustal moment of inertia ($I_{crust}/I$), mass ($M_{crust})$ and thickness ($l_{crust}$) of the crust are calculated with three unified EoSs. The crustal properties are found to be sensitive to the density-dependent symmetry energy and slope parameter advocating the importance of the unified treatment of neutron star EoS. The three unified EoSs, IOPB-I-U, FSUGarnet-U, and G3-U, reproduced the observational data obtained with different pulsars, NICER, and glitch activity and are found suitable for further description of the structure of the neutron star.

nucl-th↗

arXiv2022

Dark Matter Effects on the Compact Star Properties

The neutron star properties are generally determined by the equation of state of $β$-equilibrated dense matter. In this work, we consider the interaction of fermionic dark matter (DM) particles with the nucleons via Higgs exchange and investigate its effect on the neutron star properties with the relativistic mean-field model equation of state coupled with DM. We deduce that DM significantly affects the neutron star properties, such as considerably reduce the maximum mass of the star, which depends on the percentage of the DM considered inside the neutron star. The tidal Love numbers both for electric and magnetic cases and surficial Love numbers are also studied for DM admixed NS. It is observed that the magnitude of tidal and surficial Love numbers increase with more DM percentage. Further, we point out that post-Newtonian tidal corrections to gravitational waves decreased by increasing DM percentage. Also, the DM effect on the GW signal is significant during the late inspiral and merger stages of binary evolution for GW frequencies >500 Hz.

astro-ph.HE↗

arXiv2021

BigApple force and its implications to finite nuclei and astrophysical objects

The secondary component of the GW190814 event left us with a question, "whether it is a supermassive neutron star or lightest black-hole?". Recently, Fattoyev et al. have obtained an energy density functional (EDF) named as BigApple, which reproduces the mass of the neutron star is 2.60 $M_\odot$ which is well consistent with GW190814 data. This study explores the properties of finite nuclei, nuclear matter, and neutron stars by using the BigApple EDF along with four well-known relativistic mean-field forces, namely NL3, G3, IOPB-I, and FSUGarnet. The finite nuclei properties like binding energy per particle, skin thickness, charge radius, single-particle energy, and two-neutron separation energy are well predicted by the BigApple for a series of nuclei. The calculated nuclear matter quantities such as incompressibility, symmetry energy, and slope parameters at saturation density are consistent with the empirical or experimental values where ever available. The predicted canonical tidal deformability by the BigApple parameter set is well-matched with the GW190814 data. Also, the dimensionless moment of inertia lies in the range given by the analysis of PSR J0737-3039A.

nucl-th↗

arXiv2021

Impacts of dark matter on the $f$-mode oscillation of hyperon star

We investigate the $f$-mode oscillation of the dark matter admixed hyperon star within the relativistic Cowling approximation. The macroscopic properties are calculated with the relativistic mean-field equation of states by assuming that the dark matter particles are inside the star. The $f$-mode oscillation frequencies (only for $l=2$) are calculated with four different neutron star equation of states. We also check the effects of hyperons/dark matter and hyperons with dark matter equation of states on the $f$-mode oscillations varying with different astrophysical quantities such as mass ($M$), radius ($R$), compactness ($M/R$), surface red-shift ($Z_s$), average density ($\barρ$), dimensionless tidal deformability ($Λ$) of the neutron star. Significant changes have been seen in the $f$-mode frequencies with and without hyperons/dark matter or hyperons+dark matter. Substantial correlations are observed between canonical frequencies and $Λ$ ($f_{1.4}-Λ_{1.4}$) and maximum frequencies and canonical $Λ$ ( $f_{max}-Λ_{1.4}$).

nucl-th↗

arXiv2021

Impacts of dark matter on the curvature of the neutron star

The effects of dark matter (DM) on the curvatures of the neutron star (NS) are examined by using the stiff and soft relativistic mean-field equation of states. The curvatures of the NSs are calculated with the variation of baryon density. Also, it is found that the radial variation of the different curvatures significantly affected by the presence of DM inside the NS. The effects of DM are less pronounced on the compactness of the maximum NS mass, but still significant. The NS surface curvature is found to be more remarkable for the massive star. The binding energy of the NSs become positive with the increasing DM momentum and makes the system unstable.

nucl-th↗

arXiv2021

Effects of dark matter on the nuclear and neutron star matter

We study the dark matter effects on the nuclear matter parameters characterising the equation of states of super dense neutron-rich nucleonic-matter. The observables of the nuclear matter, i.e. incompressibility, symmetry energy and its higher-order derivatives in the presence dark matter for symmetric and asymmetric nuclear matter are analysed with the help of an extended relativistic mean-field model. The calculations are also extended to beta-stable matter to explore the properties of the neutron star. We analyse the dark matter effects on symmetric nuclear matter, pure neutron matter and neutron star using NL3, G3 and IOPB-I forces. The binding energy per particle and pressure are calculated with and without considering the dark matter interaction with the nuclear matter systems. The influences of dark matter are also analysed on the symmetry energy and its different coefficients. The incompressibility and the skewness parameters are affected considerably due to the presence of dark matter in the nuclear matter medium. We extend the calculations to the neutron star and find its mass, radius and the moment of inertia for static and rotating neutron star with and without dark matter contribution. The mass of the rotating neutron star is considerably changing due to rapid rotation with the frequency in the mass-shedding limit. The effects of dark matter are found to be important for some of the nuclear matter parameters, which are crucial for the properties of astrophysical objects.

nucl-th↗

arXiv2021

Incompressibility and Symmetry Energy of Neutron Star

We trace a systematic and consistent method to precisely numerate the magnitude range for various structural and isospin compositional properties of the neutron star. Incompressibility, symmetry energy, slope parameter and curvature of a neutron star are investigated using the relativistic energy density functional within the framework of coherent density fluctuation model. The analytical expression for the energy density functional of the neutron star matter is motivated from the Br$\ddot{u}$ckner functional and acquired by the polynomial fitting of the saturation curves for three different relativistic mean-field parameter sets (NL3, G3 and IU-FSU). The modified functional is folded with the neutron star's density-dependent weight function to calculate the numerical values for incompressibility and symmetry energy using the coherent density fluctuation model. NL3 parameter set, being the stiffest equation of state, endue us with a higher magnitude of all the properties compared to the other two parameter sets.

nucl-th↗

arXiv2021

Constraining nuclear matter parameters and neutron star observables using PREX-2 and NICER data

We try to constraints some of the nuclear matter parameters such as symmetry energy ($J$) and its slope ($L$) from the recent inferred data of the PREX-2. Other nuclear matter parameters are adopted from {\bf [Phys. Rev. C 85 035201 (2012), Phys. Rev. C 90 055203 (2014)]} papers and the linear correlation among them are checked by using the Pearson's formula. We find the correlation between $J-L$, $K_τ-J$ and $K_τ-L$ with coefficients 0.85, 0.81 and 0.76 respectively. The neutron star properties such as mass and radius are calculated with 50 unified equation of states. The results are consistent with recently observed pulsars and NICER data except few exceptions. From the radii constraints, we find that the new NICER data allows a narrow radius range contrary to a large range of PREX-2 and the old NICER data leaving us an inconclusive determination of the neutron star radius.

nucl-th↗

arXiv2021

Rotating neutron stars with quark cores

The rotating neutron star properties are studied with a phase transition to quark matter. The density-dependent relativistic mean-field model (DD-RMF) is employed to study the hadron matter, while the Vector-Enhanced Bag model (vBag) model is used to study the quark matter. The star matter properties like mass, radius,the moment of inertia, rotational frequency, Kerr parameter, and other important quantities are studied to see the effect on quark matter. The maximum mass of rotating neutron star with DD-LZ1 and DD-MEX parameter sets is found to be around 3$M_{\odot}$ for pure hadronic phase and decreases to a value around 2.6$M_{\odot}$ with phase transition to quark matter, which satisfies the recent GW190814 constraints. For DDV, DDVT, and DDVTD parameter sets, the maximum mass decreases to satisfy the 2$M_{\odot}$. The moment of inertia calculated for various DD-RMF parameter sets decreases with the increasing mass satisfying constraints from various measurements. Other important quantities calculated also vary with the bag constant and hence show that the presence of quarks inside neutron stars can also allow us to constraint these quantities to determine a proper EoS. Also, the theoretical study along with the accurate measurement of uniformly rotating neutron star properties may offer some valuable information concerning the high-density part of the equation of state.

nucl-th↗

arXiv2021

Thermal impacts on the properties of nuclear matter and young neutron star

We present a methodical study of the thermal and nuclear properties for the hot nuclear matter using relativistic-mean field theory. We examine the effects of temperature on the binding energy, pressure, thermal index, symmetry energy, and its derivative for the symmetric nuclear matter using temperature-dependent relativistic mean-field formalism for the well-known G2$^{*}$ and recently developed IOPB-I parameter sets. The critical temperature for the liquid-gas phase transition in an asymmetric nuclear matter system has also been calculated and collated with the experimentally available data. We investigate the approach of the thermal index as a function of nucleon density in the wake of relativistic and non-relativistic formalism. The computation of neutrino emissivity through the direct Urca process for the supernovae remnants has also been performed, which manifests some exciting results about the thermal stabilization and evolution of the newly born proto-neutron star. The central temperature and the maximum mass of the proto-neutron star have also been calculated for different entropy values.

hep-ph↗

arXiv2021

Effects of dark matter on the in-spiral properties of the binary neutron stars

Using the relativistic mean-field model, we calculate the properties of binary neutron star (BNS) in the in-spiral phase. Assuming the dark matter (DM) particles are accreted inside the neutron star (NS) due to its enormous gravitational field, the mass $M$, radius $R$, tidal deformability $λ$ and dimensionless tidal deformability $Λ$ are calculated at different DM fractions. The value of $M$, $R$, $λ$ and $Λ$ decreases with the increase of DM percentage inside the NS. The in-spiral phase properties of the BNS are explored within the post-Newtonian (PN) formalism, as it is suitable up to the last orbits in the in-spiral phase. We calculate the strain amplitude of the polarization waveform $h_+$ and $h_\times$, (2,2) mode waveform $h_{22}$, orbital phase $Φ$, frequency of the gravitational wave $f$ and PN parameter $x$ with DM as an extra candidate inside the NS. The magnitude of $f$, $Φ$ and $x$ are almost the same for all assumed forces; however, the in-spiral time duration in the last orbit is different. We find that the BNS with soft equation of state and a high fraction of DM sustains more time in their in-spiral phase. We suggest that one should take DM inside the NS when they modelling the in-spiral waveforms for the BNS systems.

astro-ph.HE↗