arXiv subjects

G. Mustafa

Publications and source records attributed to G. Mustafa.

At least 73 records · Page 4Linked to original sources

arXiv2024

Influence of pressure anisotropy and non-metricity parameter on mass-radius relation and stability of millisecond pulsar in $f(Q)$ gravity

In this study we explore the astrophysical implications of pressure anisotropy on the physical characteristics of millisecond pulsars within the framework of $f(Q)$ gravity, {in particular $f(Q)=-α\, Q - β$, where $α$ and $β$ are constants.} Starting off with the field equations for anisotropic matter configurations, we adopt the physically salient Durgapal-Fuloria ansatz together with a well-motivated anisotropic factor for the interior matter distribution. This leads to a nonlinear second order differential equation which is integrated to give the complete gravitational and thermodynamical properties of the stellar object. The resulting model is subjected to rigorous tests to ensure that it qualifies as a physically viable compact object within the $f(Q)$-gravity framework. We study in detail the impact of anisotropy on the mass, radius and stability of the star. Our analyses indicate that our models are well-behaved, singularity-free and can account for the existence of a wide range of observed pulsars with masses ranging from 2.08 to 2.67 $M_{\odot}$, with the upper value being in the so-called {\em mass gap} regime observed in gravitational events such as GW190814. {A comparison of the so-called {\em Symmetric Teleparallel Equivalent to GR} (STEGR) models with classical General Relativity (GR) models reveal that the anisotropy parameter and the sign of $β$ impact on the predicted radii of pulsars. In particular, STEGR models have larger radii than their GR counterparts.

gr-qc↗

arXiv2024

Observational Constraints on the Parameters of Hořava-Lifshitz Gravity

This study investigates the accelerated cosmic expansion within the Hořava-Lifshitz Model. To constrain the cosmological parameters of this model, we incorporate 17 Baryon Acoustic Oscillation points, 31 Cosmic Chronometer points, 40 Type Ia Supernovae points, 24 quasar Hubble diagram points, and 162 Gamma Ray Bursts points, along with the latest Hubble constant measurement (R22). We treat $r_{d}$ as a free parameter to extract $H_{0}$ and $r_{d}$ using late-time datasets, aiming for optimal fitting values in each model. Treating $r_{d}$ as free improves precision, reduces bias, and enhances dataset compatibility. The obtained values of $H_{0}$ and $r_{d}$ are compared to the $Λ$CDM model, showing consistency with previous estimates from Planck and SDSS studies. The Akaike Information Criterion (AIC) and Bayesian Information Criterion (BIC) favor the Hořava-Lifshitz model, with the $Λ$CDM model having the lowest AIC. Additionally, we conduct $Δ$AIC and $Δ$BIC analyses to assess model preference.} Validation using the reduced $χ_{red}^{2}$ statistic indicates satisfactory fits for the Hořava-Lifshitz model, while recognizing $Λ$CDM as the preferred model. Extensions of the analysis warrant further investigation.

astro-ph.CO↗

arXiv2024

Addressing the $r_{d}$ Tension using Late-Time Observational Measurements in a Novel deceleration Parametrization

This paper introduces a novel cosmological model aimed at probing the accelerated expansion of the late Universe through a unique parametrization of the deceleration parameter. We aim to constrain key cosmic parameters by integrating recent measurements of the Hubble parameter obtained from various observational methods, including cosmic chronometers, Type Ia Supernovae, Gamma-Ray Bursts (GRB), Quasars, and Baryon Acoustic Oscillations (BAO) from recent galaxy surveys. With a redshift range spanning $0.106 < z < 2.33$ and incorporating the latest Hubble constant measurement from Riess in 2022, our analysis yields optimal fit values for the Hubble parameter $H_{0}$ and sound horizon $r_{d}$. Notably, we uncover an inconsistency in $H_{0}$ values derived from late-time observational measurements, reflecting the well-known $H_{0}$ tension. In terms of $r_{d}$, while there is close agreement between Joint analysis and Joint analysis with R22, discrepancies arise upon gradual inclusion of BAO and BAO with R22 datasets. Our model demonstrates excellent fit to observed data and aligns well with the standard $Λ$CDM paradigm at higher redshifts. However, its most intriguing aspect lies in predicting a super-accelerated expansion in the distant future, in contrast to the de Sitter phase predicted by $Λ$CDM. Additionally, unique behaviors in the jerk parameter hint at novel dynamics beyond traditional cosmological models. Statefinder and $O_{m}$ Diagnostics tests were conducted, and comparison using the Akaike information criterion indicates neither model can be ruled out based on the latest observational measurements. These findings propose our cosmological model as a compelling alternative to $Λ$CDM, offering fresh insights into dark energy's nature and the cosmos' future.

gr-qc↗

arXiv2024

Constraining Cosmological Parameters with Viscous Modified Chaplygin Gas and Generalized Cosmic Chaplygin Gas Models in Horava-Lifshitz Gravity: Utilizing Late-time Datasets

This study examines accelerated cosmic expansion using the Viscous Modified Chaplygin Gas (VMMG) and Generalized Cosmic Chaplygin Gas (GCCM) within Horava-Lifshitz gravity. Our aim is to constrain essential cosmological parameters, such as the Hubble Parameter ($H_{0}$) and Sound Horizon ($r_{d}$). We utilize late-time datasets: 17 Baryon Acoustic Oscillation observations, 33 Cosmic Chronometer measurements, 40 Type Ia Supernovae data points, 24 quasar Hubble diagram data points, and 162 Gamma Ray Bursts data points, along with the latest determination of the Hubble constant (R22). Treating $r_{d}$ as a free parameter offers several advantages, including mitigating bias, enhancing precision, and improving compatibility with various datasets. By introducing random correlations in the covariance matrix during simulation, errors are effectively reduced. Our estimated values of the Hubble constant ($H_0$) and $r_{d}$ consistently align with measurements from both the Planck and SDSS experiments. Cosmographic tests provide valuable insights into the dynamics of various cosmological models, enriching our understanding of cosmic evolution. Statefinder diagnostics offer deeper insights into cosmic expansion dynamics, aiding in distinguishing between cosmological frameworks. Furthermore, the $o_{m}$ diagnostic test reveals that at late times, VMMG falls into the phantom region, while GCCM falls into the quintessence region. The Akaike Information Criterion (AIC) and Bayesian Information Criterion (BIC) support all models, indicating plausible explanations. Notably, the $Λ$CDM model emerges with the lowest AIC score, suggesting its relatively superior fit. Validation via the reduced $χ_{\text{red}}^{2}$ statistic confirms satisfactory fits across all models, reinforcing their credibility.

astro-ph.CO↗

arXiv2024

Gravitational Lensing of Dark Energy Models and $Λ$CDM Using Observational data in Loop Quantum Cosmology

This paper investigates the accelerated cosmic expansion in the late Universe by examining two dark energy models, viscous modified Chaplygin gas (VsMCG) and variable modified Chaplygin gas (VMCG), within loop quantum cosmology alongside the $Λ$CDM model. The objective is to constrain cosmic parameters using the $Λ$CDM model and 30 of the latest $H(z)$ measurements from cosmic chronometers (CC), including Type Ia Supernovae, Gamma-Ray Bursts (GRB), Quasars, and 24 uncorrelated baryon acoustic oscillations (BAO) measurements across a redshift range from 0.106 to 2.33. The latest Hubble constant measurement from Riess in 2022 is included to enhance constraints. In the $Λ$CDM, VsMCG, and VMCG frameworks, best-fit parameters for the Hubble parameter ($H_0$) and sound horizon ($r_d$) are obtained. The results highlight significant disparities between $H_0$ and $r_d$ values from late-time observational measurements, reflecting the known $H_0$ and $r_d$ tensions. The gravitational lensing optical depth of the two dark energy models is studied by plotting $\log(τ(z_l)/H_0^{-3} τ_N)$ vs $z_l$. The probability of finding gravitational lenses (optical depth) in both models increases with lens redshift $z_l$. The change in optical depth behavior for different parameter constraints is graphically analyzed. A joint analysis of VsMCG and VMCG with $Λ$CDM is conducted. While the models diverge in the early Universe, they are indistinguishable at low redshift. Using the Akaike information criteria, the analysis indicates that neither dark energy model can be

gr-qc↗

arXiv2024

Diagnostic and Comparative Analysis of Dark Energy Models with $q(z)$ Parametrizations

This manuscript presents a diagnostic analysis of three dark energy models resulting from the parametrization of the deceleration parameter. These models exhibit intriguing features, including late-time acceleration and a cosmological phase transition from early deceleration to late acceleration. The analysis utilizes parametrizations of the deceleration parameter, $q(z)$, and employs Cosmic Chronometers (CC), Type Ia supernovae (SNIa), Gamma Ray Bursts (GRB), Quasar (Q) and Baryon Acoustic Oscillations (BAO) datasets to constrain the models and determine the best-fitting values of the model parameters. Additionally, the evolution of kinematic cosmographic parameters is investigated. The study focuses on discussing the statefinder and Om diagnostic analyses of the considered models, comparing them with the well-established $Λ$CDM and SCDM models. By utilizing information criteria, the viability of the models is examined, assessing their goodness of fit and their ability to explain the observed data. The results provide valuable insights into the behavior and characteristics of the dark energy models. The comparison with the standard models sheds light on the similarities and differences, while the information criteria analysis offers a quantitative assessment of their suitability. This analysis contributes to our understanding of the dynamics and evolution of the universe, furthering our knowledge of dark energy and its role in shaping the cosmos.

gr-qc↗

arXiv2024

Shadow and strong gravitational lensing of new wormhole solutions supported by embedding Class-I condition

This study deals with the new class of embedded wormhole solutions in the background of general relativity. Two newly calculated wormhole solutions satisfy all the required properties. All the energy conditions are discussed through their validity regions for the different ranges of involved parameters. In maximum regions, all energy conditions are violated. We investigate the shadow and strong gravitational lensing by the wormhole throat for the two new wormhole models, namely Model-I and Model-II. The present paper considers the wormhole throat to act as a photon sphere. We first derive null geodesics using the Hamilton-Jacobi separation method to investigate the shadow and strong gravitational lensing caused by the wormhole throat. We then numerically obtain the radius of wormhole shadow, strong deflection angle, and various lensing observables by taking the example of supermassive black M87* and Sgr A* in the context of both Model-I and Model-II. Keeping all other parameters fixed, it is observed that the parameters $ζ_1$ and $ζ_2$ for Model-I; and $χ_1$ and $χ_2$ for Model-II have significant effects on the wormhole shadow and strong gravitational lensing phenomena. Our conclusion is that it is possible to detect relativistic images, such as Einstein rings, produced by wormholes with throat radii of $r_{th}=3M$. Additionally, current technology enables us to test hypotheses related to astrophysical wormholes.

gr-qc↗

arXiv2024

The estimation of parameters of generalized cosmic Chaplygin gas and viscous modified Chaplygin gas and Accretions around Black Hole in the background of Einstein-Aether gravity

In this paper, we have investigated the phenomenon of accelerated cosmic expansion in the late universe and the mass accretion process of a 4-dimensional Einstein-Aether black hole. Starting with the basics of Einstein-Aether gravity theory, we have first considered the field equations and two eminent models of Chaplygin gas, viz. generalized cosmic Chaplygin gas model and viscous modified Chaplygin gas model. Then, we obtained the energy density and Hubble parameters equations for these models in terms of some dimensionless density parameters and some unknown parameters. After finding the required parameters, we proceeded with the mass accretion process. For both models, we obtained the equation of mass in terms of the redshift function and represented the change of mass of the black hole graphically with redshift. At the same time, we have made a graphical comparison between the above-mentioned models and the $Λ$CDM model of the universe. Eventually, we have concluded that the mass of a 4-dimensional black hole will increase along the universe's evolution in the backdrop of Einstein-Aether gravity.

gr-qc↗

arXiv2024

Constraining study of charged gravastars solutions in symmetric teleparallel gravity

This study explores the effect of charge on a special astronomical object known as a gravastar, which is viewed as an alternative to a black hole. Based on the conjecture put out by Mazur and Mottola in general relativity, the study primarily focuses on the consequences of $f(Q)$ gravity. The internal domain, the intermediate shell, and the external domain are the three separate sections that make up a gravastar. Using a particular $f(Q)$ gravity model that includes conformal Killing vectors to analyze these areas, we discover that the inner domain shows a repulsive force on the spherical shell since it is assumed that pressure is equivalent to negative energy density. The intermediate shell is made up of ultrarelativistic plasma and pressure, which is proportional to energy density and balances the repulsive force from the interior domain. For exterior region, we use two appraoches as first we calculate the vacuum exact solution and secondly considered as the Reissner-Nordström metric. Then, we match these spacetimes through junction condition and explore the stability constraints for both cases. Our results show that charged gravastar solutions with non-singular physical parameters including length, energy, entropy, and equation of state parameter are physically realistic.

gr-qc↗

arXiv2024

Imprints of dark energy models on structural properties of charged gravastars in extended teleparallel gravity

A gravastar comprises three distinct sections: the interior zone, the middle shell, and its outer region. By considering a specific extended teleparallel gravity model that incorporates conformal Killing vectors and provides the field equations. We observe that the interior part exhibits a repellent force acting on the shell. This is based on the assumption that pressure is analogous to negative energy density. The middle shell consists of ultrarelativistic plasma and pressure, which is directly proportional to the matter density and counteracts the repellent force exerted by the inner zone. In the outer zone, we compute the precise solution in a vacuum and then connect these spacetimes using junction conditions to investigate stability limits. We aim to investigate the influence of dark energy models on the stable characteristics of gravastar configurations. It is worth noting that the phantom field exhibits the highest stable configurations for all physically viable selections of physical parameters. We additionally investigate the influence of physical parameters on the correct length, entropy, and energy of the gravastar.

gr-qc↗

arXiv2024

New embedded wormhole solutions in Ricci inverse gravity

In this letter, we obtain two new embedded WH solutions by using the class-I approach in the background of newly fourth-order Ricci inverse gravity. We show that the combination of these newly calculated shape functions and Ricci inverse gravity provides us with the possibility of obtaining traversable wormholes. All the required wormhole properties are discussed, along with flaring out and flatness conditions. The embedded diagrams within the scope of upper and lower universes are provided under the effect of both newly calculated embedded shape functions. All the energy conditions are explored with valid and negative regions. The presence of exotic matter is confirmed due to the negative region in all the energy conditions, specifically in the null energy condition. The Doppler effect through the red-blue shifts function is also discussed. Several key findings from the current research are described that demonstrate the validity of these wormhole solutions in Ricci inverse gravity.

gr-qc↗

arXiv2024

Dynamical stability of new wormhole solutions via cold dark matter and solitonic quantum wave halos in $f(\mathcal{R},\mathcal{L}_m)$ gravity

This current analysis offers novel wormhole solutions in the background of newly developed extended $f(\mathcal{R},\mathcal{L}_m)$ gravity. We use an anisotropic matter source and a particular type of energy density demonstrating cold dark matter halo and quantum wave dark matter halo to calculate two different wormhole solutions. The properties of the exotic matter within the wormhole geometry and the matter contents via energy conditions are studied in detail, both analytically and graphically, by showing valid and invalid regions. The calculated shape functions of wormhole geometry satisfy the required conditions in both cases. Further, we investigate the stability of the shell around wormhole structures by considering black hole solutions in the framework of cold dark matter halo and quantum wave dark matter by assuming matter contents located at the shell follow the phantom-like equations of state. Then, for quintessence and phantom energy type equations of state, the choice of cold dark matter halo has maximum stability at lower equilibrium shell radii and declines as the radius rises. More petite wormhole throats have an unstable configuration for the dark energy matter content, while higher wormhole throat radius has the lowest stability. For the choice of quantum wave dark matter, the shell around the wormhole structure is unstable for both quintessence and phantom energy, while dark energy shows a stable configuration for smaller values of wormhole throat.

gr-qc↗

arXiv2024

Cosmological Test of Dark Energy Parametrizations in Horava-Lifshitz Gravity

In this work, we assume the FRLW Universe which is filled with dark matter along with dark energy in the framework of Horava-Lifshitz (HL) gravity. The dark energy is considered as the Linear (Model I) and CPL (Model II) parametrizations of the equation of state parameter. For both models, we express the Hubble parameter $H(z)$ in terms of the model parameters and redshift $z$. To rigorously constrain the model, we have employed a comprehensive set of recent observational datasets including cosmic chronometers (CC), Type Ia Supernovae (SNIa), Baryon Acoustic Oscillations (BAO), Gamma-ray Burst (GRB), Quasar (Q) and Cosmic Microwave Background Radiation (CMB). Through the joint analysis of this diverse collection of datasets, we have achieved tighter constraints on the model's parameters. This, in turn, allows us to delve into both the physical and geometrical aspects of the model with greater precision. Furthermore, our analysis has enabled us to determine the present values of crucial cosmological parameters, including $H_{0}$, $Ω_{m0}$, $Ω_{k0}$ and $Ω_{\Lambda0}$. It's noteworthy that our results are consistent with recent findings from Planck 2018, underscoring the reliability and relevance of our models in the current cosmological context. We also conduct analysis of cosmographic parameters and apply statefinder and diagnostic tests to explore the evolution of the Universe. In addition, the AIC and BIC suggest that the $Λ$CDM model is the preferred model among all our considered models. Our investigation into the models has unveiled intriguing features of the late universe

gr-qc↗

arXiv2024

Constraints on the parameters of modified Chaplygin-Jacobi and modified Chaplygin-Abel gases in $f(T)$ gravity

In this study, we investigate two dark energy models, MCJG and MCAG, in the context of $f(T)$ gravity within a non-flat FLRW Universe. Our analysis considers radiation, dark matter, and dark energy components. We compare the equation of state for MCJG and MCAG with $f(T)$ gravity. Using recent astronomical data (e.g., $H(z)$, type Ia supernovae, Gamma Ray Bursts, quasars, and BAO), we constrain the models' parameters and explore the Universe's behavior. The reduced Hubble parameter is expressed in terms of observable parameters like $Ω_{r0}$, $Ω_{m0}$, $Ω_{k0}$, $Ω_{CJ0}$, $Ω_{CA0}$, and $H_0$. We investigate cosmic evolution using deceleration, $\mathrm{Om}$, and statefinder diagnostics. Information criteria are employed to assess model viability, comparing against the standard $Λ$CDM model. Our objective is to deepen our understanding of dark energy, its relation to $f(T)$ gravity, and the mechanisms governing the accelerated expansion of the Universe.

gr-qc↗

arXiv2024

Impact of energy-momentum conservation violation on the configuration of compact stars and their GW echoes

This work investigates the impacts of energy-momentum conservation violation on the configuration of strange stars constraint with gravitational wave (GW) event GW190814 as well as eight recent observations of compact objects. The GW echoes from these interesting classes of compact objects are also calculated. To describe the matter of strange stars, we have used two different equations of state (EoSs): first an ad-hoc exotic EoS, the stiffer MIT Bag model and next realistic CFL phase of quark matter EoS. We choose Rastall gravity as a simple model with energy-momentum conservation violation with a set of model parameter values. Our results show that this gravity theory permits stable solutions of strange stars and the resulting structures can foster GW echoes. We illustrate the implication of the gravity theory and found that the negative values of the Rastall parameter result in more compact stellar configurations and lower GW echo frequency. With an increase in the Rastall parameter, both the compactness of the stellar configurations and echo time decrease. It is worth mentioning here that with the chosen set of some probable strange star candidates from observational data and also in light of GW 190814, we have evaluated the radii of stellar models. Also, the GW echo frequencies associated with strange stars are found to be in the range of {$\approx 9-27$ kHz} for both cases. {From this work, it is also inferred that the assumption regarding the equivalence of Rastall's theory to Einstein's theory is refuted as we have noticed many deviations in the physical properties of the considered compact stars.

gr-qc↗

arXiv2024

Probing black hole in Starobinsky-Bel-Robinson gravity with thermodynamical analysis, effective force and gravitational weak lensing

In this work, we investigate the effects of plasma and the coupling parameter $β>0$, on the thermodynamic properties and weak gravitational lensing by the Schwarzschild-like black hole in the Starobinsky-Bel-Robinson gravity (SBRG). We observe that the horizon radius and the corrected entropy of the Schwarzschild-like black hole in the SBRG are not much sensitive to the parameter $β$. On contrary the energy emission rate of the Schwarzschild-like black hole in the SBRG is sensitive to the parameter $β$ and decreases with increase in the values of the parameter $β$. We see that the Schwarzschild-like black hoe in the SBRG is stable as the thermodynamicl temperature is positive for different values of the parameter $β$. Moreover we observe that the deflection angle of photon beam by the black hole in uniform plasma, nonuniform self-interacting scalar plasma and non-singular isothermal gas sphere reduces with the parameter $β$, against the impact parameter $b$. We see that the deflection angle enhances with increase in the concentration of the plasma fields for all the three types of plasma media. Further we find that the magnification of the image due to lensing increases in a higher concentration of plasma field. It is interesting to notice that the image magnification in uniform plasma is much higher as compared to the one in nonuniform plasma field. We compare our results with those for the Schwarzschild black hole of General Relativity. Further, effective force is also calculated for the current analysis.

gr-qc↗

arXiv2024

Exploring wormhole solutions in curvature-matter coupling gravity supported by noncommutative geometry and conformal symmetry

This article explores new physically viable wormhole solutions within the framework of f(R,Lm) gravity theory, incorporating noncommutative backgrounds and conformal symmetries. The study investigates the impact of model parameters on the existence and properties of wormholes. The derived shape function is found to obey all the required criteria. Specific attention is given to traceless wormholes with Gaussian and Lorentzian distributions, investigating the behavior of the shape functions and energy conditions. In both cases, the presence of exotic fluid is confirmed.

gr-qc↗

arXiv2024

Thermal analysis and Joule-Thomson expansion of black hole exhibiting metric-affine gravity

This study examines a recently hypothesized black hole, which is a perfect solution of metric-affine gravity with a positive cosmological constant, and its thermodynamic features as well as the Joule-Thomson expansion. We develop some thermodynamical quantities, such as volume, Gibbs free energy, and heat capacity, using the entropy and Hawking temperature. We also examine the first law of thermodynamics and thermal fluctuations, which might eliminate certain black hole instabilities. In this regard, a phase transition from unstable to stable is conceivable when the first law order corrections are present. Besides that, we study the efficiency of this system as a heat engine and the effect of metric-affine gravity for physical parameters $q_e$, $q_m$, $κ_{\mathrm{s}}$, $κ_{\mathrm{d}}$ and $κ_{\mathrm{sh}}$. Further, we study the Joule-Thomson coefficient, and the inversion temperature and also observed the isenthalpic curves in the $T_i -P_i$ plane. In metric-affine gravity, a comparison is made between the Van der Waals fluid and the black hole to study their similarities and differences.

gr-qc↗