arXiv subjects

M. Sharif

Publications and source records attributed to M. Sharif.

At least 37 records · Page 2Linked to original sources

arXiv2025

Charged Anisotropic Pulsar SAX J1748.9-2021 in Non-Riemannian Geometry

In this paper, we investigate the impact of charge on the stability of the pulsar star SAX J1748.9-2021 within the context of $f(\mathbb{Q}, \mathcal{T})$ theory, where $\mathbb{Q}$ and $\mathcal{T}$ represent the non-metricity scalar and the energy-momentum tensor, respectively. To achieve this, we employ the Krori-Barua metric ansatz with anisotropic fluid. We obtain exact relativistic solutions for the corresponding field equations. Additionally, we examine its physical and geometric properties using astrophysical observations of the pulsar SAX J1748.9-2021. This approach provides a basis for connecting several physical quantities, including fluid parameters, anisotropy, mass-radius relationship, compactness, redshift, \emph{energy}, the Zeldovich and causality conditions, equation of state parameter, adiabatic index and the Tolman-Oppenheimer-Volkoff equation. Our findings align with observational evidence, indicating that the pulsar SAX J1748.9-2021 remains both feasible and stable under this modified theory.

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arXiv2025

Impact of Non-metricity and Matter Source on the Geometry of Anisotropic Spheres

This paper delves into the impact of extended symmetric teleparallel theory on anisotropic compact stellar structures. The explicit field equations were formulated by considering a minimum model of this extended gravity. Basically, the Darmois junction conditions are used to determine the unknown constants of metric coefficients. We explore some significant properties of the compact stars under consideration to check their viable existence in this modified framework. The Tolman-Oppenheimer-Volkoff equation assess the equilibrium state of the compact stars. Moreover, the stability analysis is defined by using methods based on sound speed (related to how disturbances propagate in the star) and adiabatic index (related to the thermodynamic behavior of the star). We find that the proposed compact stars in the $f(\mathbb{Q}, \mathbb{T})$ gravity are physically viable and stable.

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arXiv2025

Extended Black Hole Solutions in Rastall Theory of Gravity

We utilize the gravitational decoupling via the extended geometric deformation to extend the Schwarzschild vacuum solution to new black holes in Rastall theory. By employing linear transformations that deform both the temporal and radial coefficients of the metric, the field equations with a dual matter source are successfully decoupled into two sets. The first of these sets is described by the metric for the vacuum Schwarzschild spacetime, while the second set corresponds to the added extra source. Three extended solutions are obtained using two restrictions on the metric potentials and extra source, respectively. For selected values of the Rastall and decoupling parameters, we study the impact of the fluctuation of these parameters on the obtained models. We also investigate the asymptotic flatness of the resulting spacetimes by analysis of the metric coefficients. Finally, the nature of the additional source is explored for each model, via analysis of the energy conditions. It is found among other results that none of the obtained models satisfy the energy conditions, while only the model corresponding to the barotropic equation of state mimics an asymptotically flat spacetime.

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arXiv2025

Possible Existence of Ghost Stars in the context of Electromagnetic Field

In this paper, we discuss the existence of ghost star models in the Einstein-Maxwell framework. In order to explore these objects, we put forward the idea of Zeldovich and Novikov by keeping in mind that the energy density of such models lie in the negative range in some regions of the spacetime geometry. We proceed by taking into account a static sphere and develop the field equations for a charged anisotropic fluid configuration. The two generating functions are then considered and we rewrite the field equations in terms of the mass and these physical quantities. Afterwards, we formulate two different models using the conformally flatness condition along with the considered generating functions. Further, we adopt the vanishing complexity constraint as well as null active gravitational mass to find two more solutions. The energy density for all developed models is also graphically shown. We conclude that the ghost stars exist in the presence of charge as the energy density for all the resulting solutions lie in the negative region for a particular range of the radial coordinate.

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arXiv2025

Charged Gravastar Solutions in the Finch-Skea Framework with f(\mathbb{Q}) Gravity

In this study, we investigate the features of a charged gravastar within the framework of $f(\mathbb{Q})$ gravity ($\mathbb{Q}$ represents non-metricity) using the Finch-Skea metric. This metric is applied to both the interior and shell regions of the charged gravastar and the field equations are derived accordingly. For the exterior regions, we consider various black holes, i.e., Reissner-Nordstr$\ddot{o}$m, Bardeen and Hayward regular black holes. The interior and exterior layers are matched using the Israel junction conditions, which help to determine the surface energy density and surface pressure for these black holes. We examine some physical properties such as proper length, entropy, energy and the equation of state parameter. The stability of the developed gravastar model is discussed through the effective potential, the causality condition and adiabatic index. We conclude that the compact gravastar structure could be a viable alternative to black holes within this framework.

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arXiv2025

Analyzing Gravastar Structure with the Finch-Skea Metric in Extended Modified Symmetric Teleparallel Gravity

This study analyzes the physical features of a gravastar within the $f(\mathcal{Q}, \mathbb{T})$ gravity framework, where $\mathcal{Q}$ is the non-metricity scalar and $\mathbb{T}$ is the trace of the energy-momentum tensor. Gravastars present a viable alternative to black holes, featuring a central de Sitter core, a surrounding thin shell and a dynamic layer in the Schwarzschild exterior that separates these two regions. Using the Finch-Skea metric, the necessary field equations for the core and shell are derived, while the Israel junction conditions maintain a seamless connection between the inner and outer regions. This work extensively explores crucial aspects such as energy distribution, proper length, energy conditions, entropy and the equation of state parameter. The model's stability is studied through the effective potential, redshift, causality conditions and adiabatic index. Our results highlight the essential role of modified gravity in maintaining the structural viability and stability of gravastars.

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arXiv2025

Comprehensive Study of Generalized Ghost Dark Energy in $f(\textsl{Q}, \textsl{L}_{m})$ Gravity: New Insights into Cosmic Dynamics

This paper explores the generalized ghost dark energy model in the framework of $f(\textsl{Q}, \textsl{L}_{m})$ gravity, where $\textsl{Q}$ represents the non-metricity scalar and $\textsl{L}_{m}$ denotes the matter-Lagrangian density. We take the homogeneous and isotropic universe with an ideal matter distribution and examine a scenario with interacting dark energy and dark matter. We then reconstruct $f(\textsl{Q}, \textsl{L}_{m})$ model to examine the effects of this extended gravitational framework on the cosmic evolution. The behavior of numerous cosmic parameters are explored corresponding to distinct parametric values. The stability is evaluated by the squared sound speed method. The statefinder $(r,s)$ and standard diagnostic pairs $(ω_D-ω'_{D})$ are used to study the various cosmic eras. Our results align with recent observational evidence, indicating that the $f(\textsl{Q}, \textsl{L}_{m})$ model effectively characterizes dark energy and cosmic evolution.

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arXiv2025

New Agegraphic Dark Energy Model in Modified Symmetric Teleparallel Theory

In this manuscript, we examine the cosmological significance of the new agegraphic dark energy model by investigating different cosmological parameters such as the equation of state parameter, $ω_{D}-ω^{\prime}_{D}$ and the $r-s$ planes in the framework of $f(\mathcal{Q})$ theory. We consider flat Friedmann-Robertson-Walker universe model under interacting conditions between dark energy and dark matter. The equation of state parameter indicates a quintessence-like characteristic of the universe. The stability of the model is analyzed using the squared speed of sound parameter which demonstrates the unstable behavior of the new agegraphic dark energy model throughout the cosmic evolution. The freezing region is represented by the $ω_{D}-ω^{\prime}_{D}$ plane, while the Chaplygin gas model corresponds to the $r-s$ plane. It is worthwhile to mention here that the interacting new agegraphic dark energy model addresses the cosmic coincidence problem by allowing the energy density ratio between dark energy and dark matter to evolve slowly over cosmic time.

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arXiv2024

Extending Finch-Skea Isotropic Model to Anisotropic Domain in Modified $f(\mathcal{R},\mathcal{T})$ Gravity

This paper considers the Finch-Skea isotropic solution and extends its domain to three different anisotropic interiors by using the gravitational decoupling strategy in the context of $f(\mathcal{R},\mathcal{T})$ gravitational theory. For this, we consider that a static spherical spacetime is initially coupled with the perfect matter distribution. We then introduce a Lagrangian corresponding to a new gravitating source by keeping in mind that this new source produces the effect of pressure anisotropy in the parent fluid source. After calculating the field equations for the total matter setup, we apply a transformation on the radial component, ultimately providing two different systems of equations. These two sets are solved independently through different constraints that lead to some new solutions. Further, we consider an exterior spacetime to calculate three constants engaged in the seed Finch-Skea solution at the spherical interface. The estimated radius and mass of a star candidate LMC X-4 are utilized to perform the graphical analysis of the developed models. It is concluded that only the first two resulting models are physically relevant in this modified theory for all the considered parametric choices.

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arXiv2024

Minimally Deformed Regular Bardeen Black Hole Solutions in Rastall Theory

In this study, we utilize the minimal geometric deformation technique of gravitational decoupling to extend the regular Bardeen black hole, leading to the derivation of new black hole solutions within the framework of Rastall theory. By decoupling the field equations associated with an extended matter source into two subsystems, we address the first subsystem using the metric components of the regular Bardeen black hole. The second subsystem, incorporating the effects of the additional source, is solved through a constraint imposed by a linear equation of state. By linearly combining the solutions of these subsystems, we obtain two extended models. We then explore the distinct physical properties of these models for specific values of the Rastall and decoupling parameters. Our investigations encompass effective thermodynamic variables such as density and anisotropic pressure, asymptotic flatness, energy conditions, and thermodynamic properties including Hawking temperature, entropy, and specific heat. The results reveal that both models violate asymptotic flatness of the resulting spacetimes. The violation of energy conditions indicate the presence of exotic matter, for both models. Nonetheless, the energy density, radial pressure, as well as the Hawking temperature exhibit acceptable behavior, while the specific heat and Hessian matrix suggest thermodynamic stability.

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arXiv2024

Exploring the viability of charged Spheres admitting non-metricity and matter source

This research paper investigates the impact of non-metricity and matter source on the geometry of charged spheres in the presence of anisotropic matter configuration. We use a specific model of extended symmetric teleparallel theory to minimize the complexity of the field equations. Moreover, the feasible non-singular solutions are used to examine the interior composition of the charged spheres. The Darmois junction conditions are used to determine the unknown constants in the metric coefficients. We explore some significant properties in the interior of compact stars under consideration to check their viable existence in this modified framework. The equilibrium state of the charged spheres is discussed using the Tolman-Oppenheimer-Volkoff equation and stability is analyzed by sound speed and Herrera cracking approach. We find that the charged spheres in this theoretical framework are physically viable and stable.

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arXiv2024

Viable Wormhole Structures and Energy Conditions in f(Q,T) Theory

This paper explores static wormhole solutions in f(Q,T) theory, where Q is the non-metricity and T is the trace of energy-momentum tensor. We derive the field equations that describe gravitational phenomena in the existence of non-metricity and matter source terms. We examine different models of this theory to determine the explicit expressions of matter contents, which are useful for analyzing the wormhole structures. We investigate the existence of feasible traversable wormhole solutions for constant and variable redshift functions. To determine whether physically viable wormhole geometry exists, we examine the graphical interpretation of energy constraints for different values of model parameters. It is found that realistic traversable and stable wormhole solutions exist only for the first model of this gravity.

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arXiv2024

Applicability of Modified Gauss-Bonnet Gravity Models on the Existence of Stellar Structures

In this paper, we explore the existence of spherically symmetric strange quark configurations coupled with anisotropic fluid setup in the framework of modified Gauss-Bonnet theory. In this regard, we adopt two models such as \emph{(i)} $f(\mathcal{G})=β\mathcal{G}^2$, and \emph{(ii)} $f(\mathcal{G})=δ_{1}\mathcal{G}^{x}(δ_{2}\mathcal{G}^{y}+1)$, and derive the field equations representing a static sphere. We then introduce bag constant in the gravitational equations through the use of MIT bag model, so that the quarks' interior can be discussed. Further, we work out the modified equations under the use of Tolman IV ansatz to make their solution possible. Junction conditions are also employed to find the constants involved in the considered metric potentials. Afterwards, different values of model parameters and bag constant are taken into account to graphically exploring the resulting solutions. This analysis is done by considering five strange quark objects like Her X-I, LMC X-4, 4U 1820-30, PSR J 1614-2230, and Vela X-I. Certain tests are also applied on the developed models to check their physical feasibility. It is much interesting that this modified gravity under its both considered functional forms yield physically viable and stable results for certain parametric values.

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arXiv2024

Impact of Charge on the Stability of Pulsar SAX J1748.9-2021 in Modified Symmetric Teleparallel Gravity

In this paper, we explore the effect of charge on the stability of pulsar star SAX J1748.9-2021 in $f(Q)$ gravity, where $Q$ represents non-metricity. For this purpose, we apply the Krori-Barua metric ansatz with anisotropic fluid and use a linear $f(Q)$ model $f(Q)=ζQ$, where $ζ$ is a non-zero constant. We derive exact relativistic solutions of the corresponding field equations. Furthermore, we study its geometric and physical properties through astrophysical observations from the pulsar SAX J1748.9-2021, which is found in X-ray binary systems within globular clusters. We examine features like anisotropic pressure, the mass-radius relationship, redshift, the Zeldovich condition, energy and causality conditions, the adiabatic index, the Tolman-Oppenheimer-Volkoff equation, the equation of state parameter and compactness. Our findings align with the observational data which indicate that the pulsar SAX J1748.9-2021 is viable and stable under this modified theory of gravity.

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arXiv2024

Study of Cosmic Evolution admitting Thermodynamic Analysis

This article examines the cosmic evolution in the framework of symmetric teleparallel theory, characterized by the function of non-metricity scalar $(\mathcal{Q})$. We use the e-folding number and reconstruction method with a suitable parametrization of the scale factor to obtain the functional form of symmetric teleparallel theory. Using this reconstructed model, we examine the behavior of different cosmographic parameters to demonstrate the bouncing scenarios of the cosmos by considering the contraction and expansion phases of cosmos before and after the bouncing point, respectively. It is found that the null energy condition is violated which shows that the singularity issue can be resolved in this extended theoretical framework. Moreover, we observe that the acceleration occurs near the bouncing point and the reconstructed model aligns with the current cosmic expansion. Finally, we check the validity of second law of thermodynamics in the bouncing framework of our model.

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arXiv2024

Anisotropic Stellar Models with Tolman IV Spacetime in Non-minimally Coupled Theory

This article aims to investigate various anisotropic stellar models in the background of $f(\mathcal{R},\mathcal{T},\mathcal{Q})$ gravity, where $\mathcal{Q}=\mathcal{R}_{φ\vartheta}\mathcal{T}^{φ\vartheta}$. In this regard, we adopt two standard models as $\mathcal{R}+ζ\mathcal{Q}$ and $\mathcal{R}+ζ\mathcal{R}\mathcal{Q}$, where $ζ$ symbolizes an arbitrary coupling parameter. We take spherical interior geometry and find solution to the modified gravitational field equations corresponding to each model by employing the `Tolman IV' spacetime. We need an additional constraint to close the system of field equations, thus the $\mathbb{MIT}$ bag model equation of state is chosen. The effects of modified theory on physical properties of six compact stars like PSR J 1614 2230,~SMC X-1,~Cen X-3,~PSR J 1903+327,~SAX J 1808.4-3658 and 4U 1820-30 are analyzed by using their respective masses and radii. We also determine the values of three unknowns involving in Tolman IV solution as well as the bag constant for each star at the hypersurface. Furthermore, various characteristics of the resulting solutions are examined through graphical interpretation for $ζ=\pm5$. Finally, we explore the stability of the compact objects through two different approaches. We conclude that our model-I produces physically acceptable structures corresponding to each star candidate for both values of $ζ$ whereas model-II is stable only for $ζ=5$.

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arXiv2024

Anisotropic Spherical Solutions in Rastall Gravity by Gravitational Decoupling

In this paper, we extend the Finch-Skea isotropic ansatz representing a self-gravitating interior to two anisotropic spherical solutions within the context of Rastall gravity. For this purpose, we use a newly developed technique, named as gravitational decoupling approach through the minimal geometric deformation. The junction conditions that provide the governing rules for the smooth matching of the interior and exterior geometries at the hypersurface are formulated with the outer geometry depicted by the Schwarzschild spacetime. We check the physical viability of both solutions through energy conditions for two fixed values of the Rastall parameter. The behavior of the equation of state parameters, surface redshift and compactness function are also investigated. Finally, we study the stability of the resulting solutions through Herrera cracking approach and the causality condition. It is concluded that the chosen parametric values provide stable structure only for the solution corresponding to the pressure-like constraint.

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arXiv2024

Generalized Ghost Dark Energy Model in Extended Modified Theory of Symmetric Telleparallel Gravity

This paper focuses on developing a generalized ghost dark energy model $f\mathcal{(Q,T)}$ through the correspondence scheme for a non-interacting scenario involving pressureless matter and a power-law scale factor. We analyze the cosmological implications of our model using the equation of state parameter, $ω_{GGDE}-ω'_{GGDE}$ and the $r-s$ planes. We also examine stability of the model by considering squared speed of sound parameter. The equation of state parameter shows the phantom era, while the squared speed of sound indicates a stable generalized ghost dark energy model throughout the cosmic evolution. The $ω_{GGDE}-ω'_{GGDE}$ plane depicts a freezing region, whereas the $r-s$ plane corresponds to the Chaplygin gas model. We conclude that our results are consistent with the current observational data.

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