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M. Sharif

Publications and source records attributed to M. Sharif.

At least 73 records · Page 4Linked to original sources
arXiv2024

Viable and Stable Compact Stellar Structures in $f(\mathcal{Q},\mathcal{T})$ Theory

The main objective of this paper is to investigate the impact of $f(\mathcal{Q},\mathcal{T})$ gravity on the geometry of anisotropic compact stellar objects, where $\mathcal{Q}$ is non-metricity and $\mathcal{T}$ is the trace of the energy-momentum tensor. In this perspective, we use the physically viable non-singular solutions to examine the configuration of static spherically symmetric structures. We consider a specific model of this theory to examine various physical quantities in the interior of the proposed compact stars. These quantities include fluid parameters, anisotropy, energy constraints, equation of state parameters, mass, compactness and redshift. The Tolman-Oppenheimer-Volkoff equation is used to examine the equilibrium state of stellar models, while the stability of the proposed compact stars is investigated through sound speed and adiabatic index methods. It is found that the proposed compact stars are viable and stable in the context of this theory.

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arXiv2024

Decoupled Charged Anisotropic Spherical Solutions in Rastall Gravity

This paper uses the gravitational decoupling through the minimal geometric deformation approach and extends a known isotropic solution for a self-gravitating interior to two types of anisotropic spherical solutions in Rastall gravity in the presence of electromagnetic field. By deforming only the radial metric component, the field equations are decoupled into two sets, the first of which corresponds to an isotropic distribution of matter while the second set contains the anisotropic source. We obtain a solution of the first set by employing the charged isotropic Finch-Skea ansatz, whereas a solution for the second set is obtained by adopting two mimic constraints on the pressure and density. The matching conditions at the stellar surface are explored with the exterior geometry given by the deformed Reissner-Nordstr$\ddot{o}$m spacetime. For the two fixed values of the Rastall and charge parameters, we investigate physical features of both solutions through graphical analysis of the energy conditions, equation of state parameters, surface redshift and compactness function. The stability of both solutions is also studied through the Herrera cracking approach and causality condition. We deduce that while both solutions are physically viable, only the solution corresponding to the pressure-like constraint is stable.

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arXiv2024

Influence of $f(\mathcal{R},\mathcal{T},\mathcal{Q})$ Gravity on Cylindrical Collapse

This article examines the dynamics of gravitational collapse in $f(\mathcal{R},\mathcal{T},\mathcal{Q})$ gravity, where $\mathcal{Q}=\mathcal{R}_{\mathrm{ab}}\mathcal{T}^{\mathrm{ab}}$. We consider self-gravitating anisotropic cylindrical geometry whose interior is filled with dissipative matter configuration and match it with exterior cylindrically symmetric spacetime at the hypersurface through junction conditions. We employ the Misner-Sharp and Müler-Israel Stewart formalisms to derive the dynamical as well as transport equations corresponding to the model $\mathcal{R}+Φ\sqrt{\mathcal{T}}+Ψ\mathcal{Q}$, where $Φ$ and $Ψ$ are arbitrary coupling constants. We then establish some relations between these equations through which the impact of effective matter variables, heat dissipation and the bulk viscosity on the collapse rate is studied. Further, we express the Weyl scalar in terms of the effective matter sector. We also obtain the conformal flatness by applying some restrictions on the considered model and taking dust configuration into the account. Finally, we investigate various cases to check whether the modified corrections increase or decrease the collapse rate.

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arXiv2024

Isotropic Exact Solutions via Noether Symmetries in $f(R,T,R_{μν}T^{μν})$ Gravity

In this paper, we study cosmic evolutionary stages in the background of modified theory admitting non-minimal coupling between Ricci scalar, trace of the energy-momentum tensor, contracted Ricci and energy-momentum tensors. For dust distribution, we consider isotropic, homogeneous and flat cosmic model to determine symmetry generators, conserved integrals and exact solutions using Noether symmetry scheme. We find maximum symmetries for non-minimally interacting Ricci scalar and trace of the energy-momentum tensor but none of them correspond to any standard symmetry. For rest of the models, we obtain scaling symmetry with conserved linear momentum. The graphical analysis of standard cosmological parameters, squared speed of sound, viability conditions suggested by Dolgov-Kawasaki instability and state-finder parameters identify realistic nature of new models compatible with Chaplygin gas model, quintessence and phantom regions. The fractional densities relative to ordinary matter and dark energy are found to be consistent with Planck 2018 observational data. It is concluded that the constructed non-minimally coupled models successfully explore cosmic accelerated expansion.

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arXiv2024

Charged Anisotropic Spherical Collapse in $f(\mathcal{R},\mathcal{T},\mathcal{Q})$ Gravity

This paper discusses the gravitational collapse of dynamical self-gravitating fluid distribution in $f(\mathcal{R},\mathcal{T},\mathcal{Q})$ gravity, where $\mathcal{Q}=\mathcal{R}_{φ\vartheta}\mathcal{T}^{φ\vartheta}$. In this regard, we assume a charged anisotropic spherical geometry involving dissipation flux and adopt standard model of the form $\mathcal{R}+Φ\sqrt{\mathcal{T}}+Ψ\mathcal{Q}$, where $Φ$ and $Ψ$ symbolize real-valued coupling parameters. The Misner-Sharp as well as Müler-Israel Stewart mechanisms are employed to formulate the corresponding dynamical and transport equations. We then interlink these evolution equations which help to study the impact of state variables, heat dissipation, modified corrections and charge on the collapse rate. The Weyl scalar is further expressed in terms of the modified field equations. The necessary and sufficient condition of conformal flatness of the considered configuration and homogeneous energy density is obtained by applying some constraints on the model along with disappearing charge and anisotropy. Finally, we discuss different cases to investigate how the spherical matter source is affected by the charge and modified corrections.

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arXiv2023

Greybody Factor for a Non Accelerated Charged Modified Black Hole in anti-de Sitter Regime

This paper investigates the greybody factor for a non accelerated black hole with modified Maxwell electrodynamics in an anti-de Sitter regime. For this purpose, we compute the radial equation for a massless scalar field with the help of Klein-Gordon equation. We then formulate effective potential by transforming this equation into Schrodinger wave equation. We analyze the graphical behavior of effective potential for different values of mass, parameter characterizing the modified Maxwell theory, anti-de Sitter radius and electromagnetic charge parameters. The exact solutions are computed at two different horizons, i.e., event and cosmological horizons through the radial equation. Furthermore, we match the obtained solutions in an intermediate regime to enhance feasibility of the greybody factor over the entire domain and check its behavior graphically. It is found that the greybody factor has a direct relation with the radius, electromagnetic charge as well as angular momentum of the black hole and an inverse relation with the anti-de Sitter radius and modification parameter. We conclude that the modified Maxwell solution reduces the emission rate of the black hole.

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arXiv2023

Impact of Charge on Complexity Analysis and Isotropic Decoupled Solutions in $f(\mathbb{R},\mathbb{T})$ Gravity

In this paper, we formulate two exact charged solutions to the field equations by extending the domain of existing anisotropic models with the help of minimal gravitational decoupling in $f(\mathbb{R},\mathbb{T})$ theory. For this, the anisotropic fluid distribution is considered as a seed source that is extended through the inclusion of a new gravitational source. The influence of the later matter configuration is controlled by the decoupling parameter. We formulate the field equations corresponding to the total matter source that are then decoupled into two distinct sets by implementing a transformation only on the radial metric coefficient. Both of these under-determined sets correspond to their parent sources. Some well-behaved forms of the metric potentials are taken into account to deal with the first set of equations. On the other hand, we solve the second set corresponding to an additional source by taking different constraints on the matter sector. We then consider the radius and mass of a compact star $4U~1820-30$ to analyze the physical feasibility of the resulting solutions for a particular modified model. It is concluded that our resulting solutions show stable behavior for certain values of the decoupling parameter and charge.

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arXiv2023

Study of Charged Celestial Objects in Modified Gravity

In this paper, we assess different charged self-gravitating stellar models possessing anisotropic matter source in the background of $f(G,T)$ gravity. For this purpose, we choose a well-known model of this gravity, i.e., $f(G,T)=G^2+\varrho T$, where $\varrho$ stands for the coupling constant. The modified field equations are developed using MIT bag model equation of state, and their solution is found with the help of Tolman IV ansatz which contains three unknown constants. This solution is further exploited to examine the graphical behavior of Her X-I, PSR J1614-2230, 4U1820-30 and LMC X-4 celestial objects. We assume two different values of charge to figure out the pressure constituents, energy density, anisotropy and energy constraints graphically. We also discuss compactness, mass and redshift parameters. Finally, we explore stability of the considered stars through two different methods. It is concluded that all the star candidates are viable as well as stable for $\mathcal{Q}=0.1$. For the larger charge, the viable behavior is also observed for all stars but PSR J1614-2230 shows unstable trend.

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arXiv2023

Study of Viable Charged Wormhole Solutions in $f(R,G)$ Theory

In this paper, we investigate how charge and modified terms affect the viability and stability of traversable wormhole geometry in the framework of $f(R,G)$ theory, where $R$ is the Ricci scalar and $G$ is the Gauss-Bonnet term. For this purpose, we develop a shape function through the Karmarkar condition to examine the wormhole geometry. The resulting shape function satisfies all the necessary conditions and establishes a connection between the asymptotically flat regions of the spacetime. The behavior of energy conditions and sound speed is checked in the presence of higher-order curvature terms and electromagnetic field to analyze the existence of stable traversable wormhole geometry. It is found that the traversable wormhole solutions are viable and stable in this modified theory.

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arXiv2023

Complexity of Dynamical Dissipative Cylindrical System in Non-minimally Coupled Theory

This paper aims to formulate certain scalar factors associated with matter variables for self-gravitating non-static cylindrical geometry by considering a standard model $\mathcal{R}+ζ\mathcal{Q}$ of $f(\mathcal{R},\mathcal{T},\mathcal{Q})$ gravity, where $\mathcal{Q}=\mathcal{R}_{φ\vartheta}\mathcal{T}^{φ\vartheta}$ and $ζ$ is the arbitrary coupling parameter. We split the Riemann tensor orthogonally to calculate four scalars and deduce $\mathcal{Y}_{TF}$ as complexity factor for the fluid configuration. This scalar incorporates the influence of inhomogeneous energy density, heat flux and pressure anisotropy along with correction terms of the modified gravity. We discuss the dynamics of cylinder by considering two simplest modes of structural evolution. We then take $\mathcal{Y}_{TF}=0$ with homologous condition to determine the solution for dissipative as well as non-dissipative scenarios. Finally, we discuss the criterion under which the complexity-free condition shows stable behavior throughout the evolution. It is concluded that complex functional of this theory results in a more complex structure.

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arXiv2023

Impact of $f(\Re,\mathcal{T}^{2})$ Theory on Stable Finch-Skea Gravastar Model

This paper examines the structure of a gravitationally vacuum star (also known as gravastar) in the background of ${f}(\Re,\mathcal{T}^{2})$ theory. This hypothetical object can be treated as a substitute of a black hole, with three regions: (i) the internal region, (ii) the intrinsic shell and (iii) the outer region. We examine these geometries using Finch-Skea metric for radial metric component along with particular $f(\Re,\mathcal{T}^{2})$ model. We determine singularity-free solution for both the inner as well as thin-shell domains. The smooth matching of the interior region with external Schwarzschild spacetime is obtained through Israel matching constraints. Finally, we study various characteristics of gravastar domains including equation of state parameter, proper length, entropy, energy as well as surface redshift. It is found that the compact gravastar structure is a viable alternate to the black hole in the perspective of this gravity.

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arXiv2023

Effects of Charge and Gravitational Decoupling on Complexity and Isotropization of Anisotropic Models

This paper constructs two immediate extensions of the existing anisotropic solutions in the context of Einstein-Maxwell framework by employing minimal geometric deformation. To achieve this, we assume a static spherical interior initially filled with anisotropic fluid and call it a seed source. We extend this matter configuration by including a new source whose impact on the self-gravitating system is governed by a decoupling parameter. The charged field equations analogous to the total fluid source are formulated. We then implement a transformation on the radial metric potential that divides the field equations into two new under-determined systems, corresponding to the initial and new sources. The first of them is addressed by taking two well-known metric ansatz so that the number of unknowns can be tackled. Further, the vanishing of total anisotropy and complexity-free constraints are used to solve the second set. The estimated radius and mass of a compact star $4U~1820-30$ is utilized to interpret the resulting solutions graphically for different values of the charge and decoupling parameter $ω$. We conclude that our both developed models are physically acceptable for all parametric values except $ω=1$.

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arXiv2023

Analysis of Complexity Factor for Charged Dissipative Configuration in Modified Gravity

In this paper, we determine the electromagnetic effects on the complexity factor of radiating anisotropic cylindrical geometry in the background of $f(G,\mathcal{T})$ theory. The self-gravitating objects possessing inhomogeneous energy density, pressure anisotropy, heat flux, charge and correction terms appear to encounter the complexity producing phase. Herrera's orthogonal splitting method is used to identify the scalar functions in which the factor that incorporates all of the fundamental aspects of the system is assumed to be the complexity factor. We also look at the evolution of charged cylindrical matter source by selecting homologous pattern as the most basic evolutionary mode. In addition to this, homologous and complexity free conditions are utilized to address dissipative as well as non-dissipative scenarios. The complexity producing parameters throughout the evolutionary process are assessed at the end. It is concluded that the complexity of the astrophysical entities is elevated due to the contribution of charge and modified terms of this theory.

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arXiv2023

Charged Anisotropic Tolman IV Solution in Matter-Geometry Coupled Theory

This paper discusses the interior distribution of several anisotropic star models coupled with an electromagnetic field in the context of $f(\mathcal{R},\mathcal{T},\mathcal{Q})$ gravity, where $\mathcal{Q}=\mathcal{R}_{βξ}\mathcal{T}^{βξ}$. In this regard, a standard model of this modified gravity is taken as $\mathcal{R}+ν_{3}\mathcal{R}_{βξ}\mathcal{T}^{βξ}$, where $ν_{3}$ symbolizes an arbitrary coupling constant. We assume a charged spherically symmetric metric that represents the interior geometry of compact quark stars and develop the corresponding modified field equations. These equations are then solved with the help of metric potentials of Tolman IV spacetime and a linear bag model equation of state. We consider the experimental data (i.e., radii and masses) of different quark models such as SMC X-4, SAX J 1808.4-3658, Her X-I and 4U 1820-30 to analyze how the charge and modified corrections affect their physical characteristics. The viability and stability of the resulting model is also checked for the considered star candidates with two different values of $ν_{3}$. We conclude that only two models, Her X-I and 4U 1820-30 show stable behavior in this modified framework for both values of the coupling constant.

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arXiv2023

Impact of Charge on Traversable Wormhole Solutions in $f(R,T)$ Theory

This paper examines the effects of charge on traversable wormhole structure in $f(R,T)$ theory. For this purpose, we use the embedding class-I approach to build a wormhole shape function from the static spherically symmetric spacetime. The developed shape function satisfies all the required conditions and connects two asymptotically flat regions of spacetime. We consider different models of this modified theory to examine the traversable wormhole solutions through null energy condition and also check their stable state. We conclude that viable and stable wormhole solutions are obtained under the influence of charge in this gravitational theory.

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arXiv2023

Stellar Structures admitting Noether Symmetries in $f(\mathcal{R},\mathcal{T})$ Gravity

This paper investigates the geometry of compact stellar objects via Noether symmetry strategy in the framework of curvature-matter coupled gravity. For this purpose, we assume the specific model of this theory to evaluate Noether equations, symmetry generators and corresponding conserved parameters. We use conserved parameters to examine some fascinating attributes of the compact objects for suitable values of the model parameters. It is analyzed that compact objects in this theory depend on the conserved quantities and model parameters. We find that the obtained solutions provide the viability of this process as they are compatible with the astrophysical data.

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arXiv2023

Cosmological Solutions through Gravitational Decoupling in $f(\mathcal{R},\mathcal{T},\mathcal{R}_{\mathrm{a}\mathrm{b}}\mathcal{T}^{\mathrm{a}\mathrm{b}})$ Gravity

In this paper, we adopt minimal gravitational decoupling scheme to extend a non-static spherically symmetric isotropic composition to anisotropic interior in $f(\mathcal{R},\mathcal{T},\mathcal{R}_{\mathrm{a}\mathrm{b}}\mathcal{T}^{\mathrm{a}\mathrm{b}})$ theory. A geometric deformation is applied only on $g_{rr}$ metric component through which the modified field equations are separated into two sets, each of them correspond to their parent (seed and newly added) source. An isotropic model suggested by the Friedmann-Lemaitre-Robertson-Walker metric is adopted to reduce the unknowns in the first set. We then obtain an isotropic solution by making use of a linear equation of state and a particular form of the scale factor. A density-like constraint is chosen to solve the other sector containing the deformation function and multiple components of an additional matter source. Further, the graphical interpretation of the developed model is carried out to analyze how a decoupling parameter and modified gravity influence the evolutionary phases of the universe. It is concluded that only the radiation-dominated era meets stability criteria everywhere in this matter-geometry coupled theory.

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arXiv2023

Decoupled Quark Stars Relativistic Models in the Regime of Self-interacting Brans-Dicke Gravity

In this work, we generate two static anisotropic solutions for a sphere containing quark matter in the framework of self-interacting Brans-Dicke theory. For this purpose, we add an anisotropic source in the seed distribution and decouple the field equations through deformation in the radial metric function. As a result of this transformation, the field equations are disintegrated into two systems which separately include the effects of isotropic and anisotropic sources. The system related to the additional source is solved via the MIT bag model equation of state. We consider Tolman V spacetime and Karmarkar condition to formulate two solutions for the isotropic sector which are extended to the anisotropic domain via decoupling technique. The junction conditions at the boundary determine the unknown parameters in terms of mass and radius of the spherical object. We investigate the viability and stability of the constructed strange star models in the presence of massive scalar field corresponding to three strange star candidates: Her X-1, PSR J1614-2230 and 4U 1608-52. It is concluded that the anisotropic models are well-behaved as they fulfill the necessary requirements for lower as well as higher values of the decoupling parameter.

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