arXiv subjects

Pinku Routaray

Publications and source records attributed to Pinku Routaray.

10 recordsLinked to original sources

arXiv2025

General relativistic study of $f$-mode oscillations in neutron stars with gravitationally bound dark matter

A comprehensive investigation of nonradial oscillations in neutron star (NS) admixed with gravitationally bounded dark matter (DM) is carried out within the framework of full general relativity. The relativistic mean field (RMF) formalism is employed to illustrate the hadronic equation of state (EOS), while a physically motivated, gravitationally captured, non-uniform fermionic Higgs-portal DM component is incorporated to model DM-admixed NS. The DM distribution is characterized by two free parameters: $\alpha M_\chi$, an effective control parameter that combines the DM concentration and the DM candidate mass, and $\beta$, a steepness parameter controlling the DM density distribution. The quasi normal mode (QNM) characteristics such as fundamental ($f$) mode frequency and its corresponding gravitational-wave (GW) damping time ($\tau$) is calculated for DM-admixed NS by solving the general relativistic perturbed equations involving axial as well as polar modes. The study demonstrates how the inclusion of DM distribution modifies the $f$-mode frequency and enhances the damping rate, reflecting a stronger coupling between matter and spacetime perturbations. Considering DM effects, the correlation analysis among DM model parameters, NS observables and QNM characteristics also carried out. Analytic fits for the $f-C-\tau$ and $f-\Lambda -\tau$ relations are constructed and calibrated for DM-admixed NS models. Building upon asteroseismic universal relations (URs), multimessenger constraint from the GW170817 event is employed by mapping the tidal deformability $\Lambda_{1.4}$ into the $(f_{1.4},\tau_{1.4})$ space, thereby providing observational bounds on the oscillation properties of canonical DM-admixed NS model.

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arXiv2024

Effects of asymmetric dark matter on a magnetized neutron star: A two-fluid approach

We study the interaction between dark matter (DM) and highly magnetized neutron stars (NSs), focusing on how DM particle mass, mass fraction, and magnetic field (MF) strength affect NS structure and stability. We consider self-interacting, nonannihilating, asymmetric fermionic DM that couples to NSs only through gravitational interaction. Using the Quantum Monte Carlo Relativistic Mean Field (QMC-RMF4) model with density-dependent magnetic fields, we investigate the magnetized equation of state and examine the accumulation of DM under various conditions. Our results show that as the DM fraction increases, the maximum gravitational mass of the NS decreases, especially for heavier DM particles, while lighter DM particles can induce a transition from a dark core to a halo structure, increasing the maximum mass. Strong MFs soften the equation of state and reduce the dark mass a NS core can retain before transitioning to a halo. By comparing our results with observations from Neutro Star Interior Composition Explorer and GW170817, we identify the possible range of DM parameters for these objects. We find that the magnetic field slightly changes these limits, mainly affecting the maximum NS mass and tidal deformability. These findings provide key insights into how DM and MF jointly shape the mass-radius relation and the stability of DM-admixed magnetized NSs.

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arXiv2024

Decoding Dark Matter Admixed Neutron Stars: From Static Structure to Rotational Deformation

In this study, we investigate the impacts of dark matter (DM) on the properties of both static and rotating neutron stars utilizing a self-interacting DM model, motivated by the neutron decay anomaly. DM-admixed NSs are modeled by assuming chemical equilibrium between ordinary matter and the dark sector, treating a single-fluid Tolman-Oppenheimer-Volkoff (TOV) framework. By treating the DM interaction strength ($G$) as a free parameter, we explore its influence on NS properties, considering a broad range of equations of state (EoSs). Using the mass-radius constraints from NICER pulsar measurements, we constrain the DM interaction strength for each EoS via a likelihood analysis. Extending this model to rotating NSs, we analyze how centrifugal forces associated with increasing angular velocity ($\Omega$) enhance both mass and radius, causing deformation. We assess the impact of DM on rotational deformation by calculating the eccentricity, highlighting the interplay between DM and rotational forces. Since both DM and rotation simultaneously influence NS properties, we compute the relative changes in mass and radius across varying $G$ and $\Omega$ values to quantify their combined effects.

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arXiv2024

Exploring the Macroscopic Properties and Nonradial Oscillations of Proto-Neutron Stars: Effects of Temperature, Entropy, and Lepton Fraction

Neutron stars (NSs) have traditionally been viewed as cold, zero-temperature entities. However, recent progress in computational methods and theoretical modelling has opened up the exploration of finite temperature effects, marking a novel research frontier. This study examines Proto-Neutron Stars (PNSs) using the BigApple parameter set to investigate their macroscopic properties. Two approaches are employed: one with constant temperatures (10-50 MeV) and the other fixing entropy per baryon (S) at predefined levels (S = 1 and S = 2). Notably, S remains constant with increasing baryon density due to electron-positron pair formation at finite temperatures. Analysis of PNS mass-radius profiles, considering neutrino trapping and temperature effects, reveals flattened curves and expanded radii with increasing temperature, resulting in slightly higher masses compared to zero temperature. The influence of lepton fraction ($Y_l$) on maximum PNS mass is explored, indicating that higher $Y_l$ values lead to a softer Equation of State (EoS), reducing maximum mass and increasing the canonical radius ($R_{1.4}$). Further investigation of a constant entropy EoS demonstrates that higher entropy is associated with increased maximum PNS masses and flatter mass-radius curves. Central temperature versus maximum mass relationships suggest a correlation between NS mass and temperature. Lastly, we investigate the behaviour of $f$-mode frequencies in PNS. It reveals that the frequency of these modes decreases with increasing entropy and temperature, reflecting complex thermodynamic interactions within the stars.

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arXiv2024

The Impact of Anisotropy on Neutron Star Properties: Insights from I-f-C Universal Relations

This study presents a universal relation for anisotropic neutron stars, called the $I-f-C$ relation, which accounts for the local anisotropic pressure using the Quasi-Local (QL) Model proposed by Horvat et al. \cite{QL_Model} to describe the anisotropy inside the neutron star. This study analyzes approximately 60 unified tabulated EoS-ensembles, spanning from relativistic to non-relativistic mean-field models, that comply with multimessenger constraints and cover a broad range of stiffness. The results indicate that the relationship between the parameters becomes more robust with positive anisotropy, while it weakens with negative anisotropy. With the help of the GW170817 \& GW190814 tidal deformability limit, a theoretical limit for the canonical $f$-mode frequency for both isotropic and anisotropic stars is established. For isotropic case the canonical $f$-mode frequency for event GW170817 \& GW190814 is $f_{1.4} = 2.605^{+0.487} _ {-0.459}\ \mathrm{kHz}$ and $ f_{1.4} = 2.093^{+0.150} _ {-0.125} \ \mathrm{kHz}$ respectively. These established relationships have the potential to serve as a reliable tool to limit the equation of state of nuclear matter when measurements of relevant observables are obtained.

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arXiv2023

Investigating Dark Matter-Admixed Neutron Stars with NITR Equation of State in Light of PSR J0952-0607

The fastest and heaviest pulsar, PSR J0952-0607, with a mass of $M=2.35\pm0.17 \ M_\odot$, has recently been discovered in the disk of the Milky Way Galaxy. In response to this discovery, a new RMF model, `NITR' has been developed. The NITR model's naturalness has been confirmed by assessing its validity for various finite nuclei and nuclear matter properties, including incompressibility, symmetry energy, and slope parameter values of 225.11, 31.69, and 43.86 MeV, respectively. These values satisfy the empirical/experimental limits currently available. The maximum mass and canonical radius of a neutron star (NS) calculated using the NITR model parameters are 2.355 $M_\odot$ and 13.13 km, respectively, which fall within the range of PSR J0952-0607 and the latest NICER limit. This study aims to test the consistency of the NITR model by applying it to various systems. As a result, its validity is extensively calibrated, and all the nuclear matter and NS properties of the NITR model are compared with two established models such as IOPB-I and FSUGarnet. In addition, the NITR model equation of state (EOS) is employed to obtain the properties of a dark matter admixed NS (DMANS) using two approaches (I) single-fluid and (II) two-fluid approaches. In both cases, the EOS becomes softer due to DM interactions, which reduces various macroscopic properties such as maximum mass, radius, tidal deformability, etc. The various observational data such as NICER and HESS are used to constrain the amount of DM in both cases. Moreover, we discuss the impact of dark matter (DM) on the nonradial $f$-mode frequency of the NS in a single fluid case only and try to constrain the amount of DM using different theoretical limits available in the literature.

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arXiv2023

Probing the Impact of WIMP Dark Matter on Universal Relations, GW170817 Posterior and Radial Oscillations

In this study, we investigate the impact of Weakly Interacting Massive Particles (WIMPs) dark matter (DM) on $C-Λ$ universal relations, GW170817 posterior and radial oscillations of neutron stars (NSs) by considering the interactions of uniformly trapped neutralinos as a DM candidate with the hadronic matter through the exchange of the Higgs boson within the framework of the Next-to-Minimal Supersymmetric Standard Model (NMSSM). The hadronic equation of state (EOS) is modeled using the relativistic mean-field (RMF) formalism with IOPB-I, G3, and QMC-RMF series parameter sets. Presence of DM softens the EOS at both the background and the perturbation levels that implies a small shift to the left in the posterior accompanied by a much larger jump in the left of the mass-radius curves with increasing DM mass. It is observed that EOSs with DM also satisfy the $C-Λ$ universality relations among their-selves but get slightly shifted to the right in comparison to that without considering DM. Additionally, we find that the inclusion of DM allows the mass-radius ($M-R$) curves to remain consistent with observational constraints for HESS J1731-347, indicating the possibility of classifying it as a dark matter-admixed neutron star (DMANS). Moreover, we explore the impact of DM on the radial oscillations of pulsating stars and investigate the stability of NSs. The results demonstrate a positive correlation between the mass of DM and the frequencies of radial oscillation modes.

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arXiv2023

Probing the impact of Delta-Baryons on Nuclear Matter and Non-Radial Oscillations in Neutron Stars

The presence of heavy baryons, such as $\Delta$-baryons and hyperons can significantly impact various properties of Neutron Stars (NSs), like oscillation frequencies, dimensionless tidal deformability, mass, and radii. We explored these effects within the Density-Dependent Relativistic Mean Field formalism. Our analysis considered $\Delta$-admixed NS matter in both hypernuclear and hyperon-free scenarios, providing insights into particle compositions and their effects on NS properties. Our study of non-radial $f$-mode oscillations revealed a distinct increase in frequency due to the additional baryons. The degree of increase was significantly influenced by the meson-baryon coupling strengths. Notably, the coupling between $\Delta$-resonances and $\sigma$-mesons played a highly influential role. In some cases, it led to an approximately 20\% increase in the $f$-mode oscillation frequency of canonical NSs. These couplings also affect other bulk properties of NSs, including mass, radii, and dimensionless tidal deformability ($\Lambda$). Comparing our results with available observational data from pulsars (NICER) and gravitational waves (LIGO-VIRGO collaboration), we found strong agreement, particularly concerning $\Lambda$.

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arXiv2023

Constraining neutron star properties and dark matter admixture with the NITR-I equation of state: Insights from observations and universal relations

A recent observational study has constrained the maximum mass of neutron stars (NSs), with particular attention to PSR J0952-0607 and the compact star remnant HESS J1731-347, especially in the low-mass regime. Building on our earlier work, which developed the NITR energy density functional (EDF) to reproduce the mass limit of PSR J0952-0607 but did not satisfy other observational constraints, this study introduces a refined EDF named ``NITR-I". NITR-I successfully reconciles the PSR J0952-0607 mass limit with observational data, including radius measurements from NICER+XMM and tidal deformability constraints from GW170817, demonstrating its robustness. The low-mass constraint associated with HESS J1731-347 indicates diverse NS compositions. Since NITR-I alone cannot satisfy this constraint, we explore the role of dark matter (DM) within NSs to bridge the gap. Incorporating DM, particularly at specific Fermi momentum values, enables the model to address this constraint. We further analyze the influence of DM on various NS properties, such as tidal deformability and non-radial $f$-mode oscillations, across multiple relativistic mean-field models. The presence of DM suggests a reduction in tidal deformability and shifts in oscillation frequencies, potentially offering detectable signatures in gravitational wave observations from neutron star mergers. Additionally, we investigate universal relations (URs) for DM-admixed NSs, focusing on correlations such as compactness versus tidal deformability and $f$-mode frequency versus tidal deformability. Canonical values for these properties are estimated using GW170817 data, offering further insights into the structure and composition of neutron stars.

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arXiv2022

Radial oscillations in neutron stars from unified hadronic and quarkyonic equation of states

We study radial oscillations in non-rotating neutron stars by considering the unified equation of states (EoSs), which support the 2 M$_\odot$ star criterion. We solve the Sturm-Liouville problem to compute 20 lowest radial oscillation modes and their eigenfunctions for neutron star modelled with eight selected unified EoSs from distinct Skyrme-Hartree Fock, Relativistic Mean-Field and quarkyonic models. We compare the behavior of the computed eigenfrequency for NS modelled with hadronic to that with quarkyonic EoSs while varying central densities. The lowest order, f-mode frequency varies substantially between the two classes of the of EoS at 1.4 M$_\odot$ but vanishes at their respective maximum masses, consistent with the stability criterion $\partial M/\partialρ_c > 0$. Moreover, we also computed large frequency separation and discovered that higher-order mode frequencies are significantly reduced by incorporating crust in the EoS.

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