arXiv subjects

J. Sedaghat

Publications and source records attributed to J. Sedaghat.

9 recordsLinked to original sources

arXiv2026

Microscopic Interaction versus Purely Gravitational Coupling in Strange Quark Stars Admixed with Dark Matter: A One-Fluid and Two-Fluid Comparison

In this study, we investigate strange quark stars (SQSs) admixed with scalar dark matter (DM), focusing on the role of microscopic interactions versus purely gravitational coupling. Our results demonstrate that while the interacting one-fluid model yields viable configurations with M_TOV > 2M_sun that satisfy current pulsar M-R measurements alongside the tidal deformability (Lambda) constraints from GW170817, the noninteracting two-fluid model more robustly meets both existing GW170817 limits and the tighter Lambda bounds anticipated from next-generation gravitational-wave detectors.

astro-ph.HE↗

arXiv2026

Two fluid CFL strange quark stars with scalar dark matter: critical mass and mass gap implications

We investigate the structure of strange quark stars (SQSs) in the color--flavor--locked (CFL) phase in the presence of scalar bosonic dark matter within a two--fluid formalism employing perturbative QCD. By considering different dark matter masses and varying the pairing gap $\Delta$ and {the central dark matter pressure fraction} $f_r$, we analyze the impact of dark matter on the structural properties of SQSs, including the maximum gravitational mass $M_{\mathrm{TOV}}$, the ratio of dark matter to strange-quark-matter radii $R_{\mathrm{DM}}/R_{\mathrm{SQM}}$, and the dimensionless tidal deformability $\Lambda$. We further examine the compatibility of the resulting mass--radius relations with the recent NICER measurements of compact stars. Within the parameter space considered in this study, we find that $M_{\mathrm{TOV}}$ exhibits a non-monotonic dependence on the dark matter mass, with a critical value beyond which $M_{\mathrm{TOV}}$ decreases. We also show that some pure CFL strange quark star configurations, particularly those associated with very stiff EOSs and larger maximum masses, may not simultaneously remain compatible with the $\Lambda$ range inferred from GW170817 while occupying the lower mass--gap region. In contrast, the inclusion of dark matter allows two-fluid CFL strange quark star configurations to reproduce the observed properties of massive compact objects in the lower mass--gap region, such as the secondary component of GW190814, while remaining qualitatively compatible with the $\Lambda$ range inferred from GW170817. We note, however, that the GW170817 constraints were originally inferred within single-fluid compact-star frameworks and therefore provide only {qualitative guidance} for the present two-fluid halo configurations. Our results suggest that exotic compact-star configurations may populate part of the conventionally defined lower mass--gap region.

astro-ph.HE↗

arXiv2026

Structure of Anisotropic Magnetized Neutron Stars in f(R,T) Gravity with Realistic Equation of State

In this study, within the framework of f(R,T) modified gravity, we investigate the influence of coupling parameter, magnetic field and anisotropy parameter on the neutron star structure. This work employs an accurate equation of state (EoS), derived from realistic microscopic calculations based on the AV18 nucleon-nucleon potential, to compute the structure of this compact object. Here, determination of Schwarzschild radius, compactness, gravitational surface redshift and Kretschmann scalar within the f(R, T) gravity, confirms that our theoretical results are consistent with the observational constraints. While established physical EoSs within the framework of Einstein gravity have successfully characterized a broad range of compact objects, they remain inadequate in explaining certain massive objects residing within the mass gap (2.5 to 5 Msun). We show that some compact objects residing in the mass gap interpreted as candidates of neutron stars within the framework of f(R, T) gravity. Finally, we compare our results with the observational data from LIGO/Virgo/KAGRA and NICER, setting the parameters of the f(R, T) theory and anisotropy to successfully reproduce the masses and radii of the GW170817, PSR J0952-0607 and PSR J0740+6620 and the masses of the secondary components of GW190814 and GW200210-092254.

gr-qc↗

arXiv2025

Influence of dark matter on the structure of strange quark stars in one-fluid model

This work studies the influence of scalar dark matter on the structural properties of strange quark stars (SQS) within a one-fluid framework, considering Yukawa interactions between dark matter and quark matter. Contributions from perturbative QCD, Yukawa interaction between scalar dark matter and quarks, and Bose-Einstein condensation of dark matter are included in the model. We first determine the allowable range of Yukawa interaction coupling by imposing the stability condition for strange quark matter (SQM). Using this range, we derive the equation of state (EOS) for different fractions of dark matter within the total pressure of SQS. These fractions are constrained by the tidal deformability limit from GW170817. The presence of dark matter alters the EOS, leading to changes in the mass-radius relationship, tidal deformability, and stability of SQS. We demonstrate that increasing the mass of dark matter softens the EOS, whereas higher fractions of dark matter lead to stiffer EOSs. We also explore the reasons behind this behavior. Our EOSs not only describe massive objects, such as PSR J0952-0607 and PSR J2215+5135, but also satisfy the tidal deformability constraint from GW170817. These results reveal that incorporating dark matter modifies the EOS, enabling the support of higher stellar masses while maintaining consistency with observational data.

hep-ph↗

arXiv2024

Constraint on the equation of state of strange quark star: Perturbative QCD along with a density-dependent bag constant

This study investigates the structural properties of strange quark stars (SQS) using a Quantum Chromodynamics (QCD) perturbative model combined with the latest Particle Data Group dataset. Given the energy scale present in compact stars, QCD perturbation theory alone may not fully explain their structure. To account for non-perturbative contributions, we incorporate a density-dependent effective bag parameter, $B$, and derive the equation of state (EOS) for strange quark matter (SQM). We start by demonstrating the limitations of EOSs with a constant $B$ in describing massive objects with $ M_{TOV}> 2M_{\odot} $. Subsequently, we show that considering $B$ as a density-dependent function significantly changes the results. Our definition of $B$ includes two parameters determined by both theoretical and observational constraints. We demonstrate that incorporating a density-dependent $B$ into the perturbative EOS can yield SQSs with masses exceeding $2M_{\odot}$, while complying with gravitational wave constraints such as tidal deformability, and thermodynamic considerations, including stability conditions and speed of sound behavior. Specifically, we show that massive compact objects like PSR J0952-0607, PSR J2215+5135, PSR J0740+6620, and the secondary mass of GW190814 can be SQSs. Additionally, we compare our EOS with the EOS of the authors who use a generalized polytropic form with adjustable parameters and obtain an interesting result.

astro-ph.HE↗

arXiv2024

Quark stars in massive gravity might be candidates for the mass gap objects

We have investigated the structural properties of strange quark stars (SQSs) in a modified theory of gravity known as massive gravity. In order to obtain the equation of state (EOS) of strange quark matter, we have employed a modified version of the Nambu-Jona-Lasinio model (MNJL) which includes a combination of NJL Lagrangian and its Fierz transformation by using weighting factors ($1-\alpha $) and $\alpha$. Additionally, we have also calculated dimensionless tidal deformability ($\Lambda$) in massive gravity. To constrain the allowed values of the parameters appearing in massive gravity, we have imposed the condition $\Lambda_{1.4 {M}_{\odot }}\lesssim580 $. Notably, in the MNJL model, the value of $\alpha$ varies between zero and one. As $\alpha$ increases, the EOS becomes stiffer, and the value of $\Lambda$ increases accordingy. We have demonstrated that by softening the EOS with increasing the bag constant, one can obtain objects in massive gravity that not only satisfy the constraint $\Lambda_{1.4 {M}% _{\odot }}\lesssim580$, but they also fall within the unknown mass gap region ($2.5{M}_{\odot}-5{M}_{\odot }$). To establish that the obtained objects in this region are not black holes, we have calculated Schwarzschild radius, compactness, and $\Lambda_{{M_{TOV}}}$ in massive gravity.

gr-qc↗

arXiv2023

Three-dimensional accelerating AdS black holes in $F(R)$ gravity

Considering a three-dimensional $C-$metric, we obtain the exact accelerating black holes in the $F(R)$ theory of gravity coupled with and without a matter field. First, we extract uncharged accelerating AdS black hole solutions in $F(R)$ gravity. Then, we study the effects of various parameters on metric function, roots, and the temperature of these black holes. The temperature is always positive for the radii less than $\frac{1}{α}$, and it is negative for the radii more than $\frac{1}{α}$. We extend our study by coupling nonlinear electrodynamics as a matter filed to $F(R)$ gravity to obtain charged black holes in this theory. Next, we evaluate the effects of different parameters such as the electrical charge, accelerating parameter, angular, $F(R)$ gravity, and scalar curvature on the obtained solutions, roots, and temperature of three-dimensional charged accelerating AdS black holes. The results indicate that there is a root in which it depends on various parameters. The temperature of these black holes is positive after this root.

gr-qc↗

arXiv2022

Is the remnant of GW190425 a strange quark star?

This study investigates the effects of different QCD models on the structure of strange quark stars (SQS). In these models, the running coupling constant has a finite value in the infrared region of energy. By imposing some constraints on the strange quark matter (SQM) and exploiting the analytic and background perturbation theories, the equations of states for the SQM are obtained. Then, the properties of SQSs in general relativity are evaluated. By using component masses of GW190425 \cite{Abbott2020ApJL} as well as some conversion relations between the baryonic mass and the gravitational mass, the remnant mass of GW190425 is obtained. Our results for the maximum gravitational mass of SQS are then compared with the remnant mass of GW190425. The results indicate that the obtained maximum gravitational masses are comparable to the remnant mass of GW190425. Therefore, it is proposed that the remnant mass of GW190425 might be a SQS.

gr-qc↗

arXiv2022

Structure of magnetized strange quark star in perturbative QCD

We have performed the leading order perturbative calculation to obtain the equation of state (EoS) of the strange quark matter (SQM) at zero temperature under the magnetic field B = 10^18 G. The SQM comprises two massless quark flavors (up and down) and one massive quark flavor(strange). Consequently, we have used the obtained EoS to calculate the maximum gravitational mass and the corresponding radius of the magnetized strange quark star (SQS). We have employed two approaches, including the regular perturbation theory (RPT) and the background perturbation theory (BPT). In RPT the infrared (IR) freezing effect of the coupling constant has not been accounted for, while this effect has been included in BPT. We have obtained the value of the maximum gravitational mass to be more than three times the solar mass. The validity of isotropic structure calculations for SQS has also been investigated. Our results show that the threshold magnetic field from which an anisotropic approach begins to be significant lies in the interval 2*10^18G < B < 3*10^18G. Furthermore, we have computed the redshift, compactness and Buchdahl-Bondi bound of the SQS to show that this compact object cannot be a black hole.

hep-ph↗