arXiv subjects

S. M. Zebarjad

Publications and source records attributed to S. M. Zebarjad.

At least 19 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 $Δ$ 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 $Λ$. 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 $Λ$ 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 $Λ$ 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↗

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↗

arXiv2025

The effect of three-body nucleon-nucleon interaction on the ground state binding energy of the light nuclei

We calculate the ground state binding energies of the light nuclei such as 4He, 6Li, 12C and 14N by considering the effect of three-body nucleon-nucleon interaction. We use the effective twobody potential obtained from the lowest order constrained variational (LOCV) calculations of the nuclear matter for the Reid68, AV14, UV14, and AV18 nuclear potentials in different channels. To calculate the ground state binding energy, we implement the local density approximation by using the harmonic oscillator wave functions while the effect of three-body interaction is considered by employing the UIX potential. We compare the obtained two-body ground state binding energy with the energy related to the three-body effect. We also compare the obtained values with the experimental data and also work of others, and show that the results are relatively acceptable. We compute the root mean-square radius Rrms of the above nuclei for the Reid68, AV14, UV14, and AV18 potentials and compare the results with the experiment. We also obtain the contribution of different channels by matching to the experimental values of the quadrupole moments and magnetic dipole moments. Furthermore, we calculate the three-body cluster energy of the above nuclei and compare the results with that of nuclear matter. According to the obtained results, we see that the three-body cluster energy contribution is small. For example, for 4He nuclide, this value is 0.079 MeV with the Reid68 potential.

nucl-th↗

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 ($1-α$) and $α$. Additionally, we have also calculated dimensionless tidal deformability ($Λ$) in massive gravity. To constrain the allowed values of the parameters appearing in massive gravity, we have imposed the condition $Λ_{1.4 {M}_{\odot }}\lesssim580 $. Notably, in the MNJL model, the value of $α$ varies between zero and one. As $α$ increases, the EOS becomes stiffer, and the value of $Λ$ 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 $Λ_{1.4 {M}% _{\odot }}\lesssim580$, 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 $Λ_{M_{TOV}}$ in massive gravity.

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↗

arXiv2020

Thermodynamics and reentrant phase transition for logarithmic nonlinear charged black holes in massive gravity

We investigate a new class of $(n+1)$-dimensional topological black hole solutions in the context of massive gravity and in the presence of logarithmic nonlinear electrodynamics. Exploring higher dimensional solutions in massive gravity coupled to nonlinear electrodynamics is motivated by holographic hypothesis as well as string theory. We first construct exact solutions of the field equations and then explore the behavior of the metric functions for different values of the model parameters. We observe that our black holes admit the multi-horizons caused by a quantum effect called anti-evaporation. Next, by calculating the conserved and thermodynamic quantities, we obtain a generalized Smarr formula. We find that the first law of black holes thermodynamics is satisfied on the black hole horizon. We study thermal stability of the obtained solutions in both canonical and grand canonical ensembles. We reveal that depending on the model parameters, our solutions exhibit a rich variety of phase structures. Finally, we explore, for the first time without extending thermodynamics phase space, the critical behavior and reentrant phase transition for black hole solutions in massive gravity theory. We realize that there is a zeroth order phase transition for a specified range of charge value and the system experiences a large/small/large reentrant phase transition due to the presence of nonlinear electrodynamics.

gr-qc↗

arXiv2015

Lepton polarization and CP-violating effects in $\overline{B}\rightarrow \overline{K}_{0}^{*}(1430) \ell^+\ell^-$ Decay in Standard and Two Higgs Doublet Model

In this paper we analyze the dilepton mass square $q^2$ dependency of single lepton polarization asymmetries and CP violation for $\overline{B}\rightarrow \overline{K}_0^{*}(1430) \ell^+\ell^-, \ell=μ,τ)$ in the 2HDM context. Also, we study the averages of these asymmetries in the domain $4 m_{\ell}^2<q^2< (m_B-m_{{K}_0^{*}})^2$. Our study manifests that the investigation of the above-mentioned asymmetries for $\overline{B}\rightarrow \overline{K}_0^*(1430) \ell^+\ell^-$ processes could provide useful information for probing new Higgs bosons in the future B-physics experiments.

hep-ph↗

arXiv2008

Double-Lepton Polarization Asymmetries in $B_s \rar ϕ\ell^+ \ell^-$ Decay in the Fourth-Generation Standard Model

In this paper, we investigate the effects of the fourth generation of quarks on the double-lepton polarization asymmetries in the $B_s \rar ϕ\ell^+ \ell^-$ decay. It is shown that these asymmetries in $B_s \rar ϕ\ell^+ \ell^-$ decay compared with those of $B \rar K \ell^+ \ell^-$ decay are more sensitive to the fourth-generation parameters. We conclude that an efficient way to establish the existence of the fourth generation of quarks could be the study of these asymmetries in the $B_s \rar ϕ\ell^+ \ell^-$ decay.

hep-ph↗

arXiv2008

Lowest Order Constrained Variational Calculation of Structure Properties of Protoneutron Star

We calculate the structure properties of protoneutron star such as equation of state, maximum mass, radius and temperature profile using the lowest order constrained variational method. We show that the mass and radius of protoneutron star decrease by decreasing both entropy and temperature. For the protoneutron star, it is shown that the temperature is nearly constant in the core and drops rapidly near the crust.

astro-ph↗

arXiv2008

Critical Behavior of Liquid 3He

We investigate the liquid-gas second-order phase transition in liquid $^3He$ using the variational calculations based on the cluster expansion of the energy functional. We also compute the critical point exponents of liquid $^3He$ which are in agreement with experimental data.

cond-mat.stat-mech↗

arXiv2008

Spin polarized liquid 3He

We have employed the constrained variational method to study the influence of spin polarization on the ground state properties of liquid $^3{\rm He}$. The spin polarized phase, we have found, has stronger correlation with respect to the unpolarized phase. It is shown that the internal energy of liquid $^3{\rm He}$ increases by increasing polarization with no crossing point between polarized and unpolarized energy curves over the liquid density range. The obtained internal energy curves show a bound state, even in the case of fully spin polarized matter. We have also investigated the validity of using a parabolic formula for calculating the energy of spin polarized liquid $^3{\rm He}$. Finally, we have compared our results with other calculations.

cond-mat.stat-mech↗

arXiv2008

Analysis of the Rare $B_c \to D_{s,d}^{*} l^+ l^-$ Decays in QCD

The rare $B_c \to D_{s,d}^{*} l^+ l^-$ decays are investigated in the framework of the three point QCD sum rules approach. Considering the gluon condensate corrections to the correlation function, the form factors relevant to these transitions are calculated. The total decay width and branching ratio for these decays are also evaluated. The results for the branching ratios are in good agreement with the quark models.

hep-ph↗

arXiv2008

The Effects of Fourth Generation on the double Lepton Polarization in B \rar K \ell^+ \ell^- decay

This study investigates the influence of the fourth generation quarks on the double lepton polarizations in B \rar K \ell^+ \ell^- decay. Taking |V_{t's}V_{t'b}|\sim \{0.01-0.03\} with phase about 100^\circ, which is consistent with the b\to s\ell^+\ell^- rate and the B_s mixing parameter Delta m_{B_s}$, we obtain that the double lepton(muon and tau) polarizations are quite sensitive to the existence of fourth generation. It can serve as a good tool to search for new physics effects, precisely, to indirect search for the fourth generation quarks(t', b').

hep-ph↗

arXiv2004

Relativistic Kinetic Vertex in Positronium

We derive Spinless Salpeter equation for the positronium using the NRQED Lagrangian. Consequently, we consider the Spinless Salpeter wavefunction instead of the Schrodinger wavefunction to show that the NRQED calculation can be done easier. We also discuss that the singularity of the Spinless Salpeter wavefunction at the origin is necessary to cancel the ultraviolet divergence in the NRQED calculations.

hep-ph↗

arXiv2002

Soliton Decay in Coupled System of Scalar Fields

A system of coupled scalar fields is introduced which possesses a spectrum of massive single-soliton solutions. Some of these solutions are unstable and decay into lower mass stable solitons. Some properties of the solutions are obtained using general principles including conservations of energy and topological charges. Rest energies are calculated via a variational scheme, and the dynamics of the coupled fields are obtained by solving the field equations numerically.

hep-th↗