arXiv subjects

M. Sharif

Publications and source records attributed to M. Sharif.

At least 91 records · Page 5Linked to original sources

arXiv2023

Influence of Charge on Anisotropic Class-one Solution in Non-minimally Coupled Gravity

This paper studies charged star models associated with anisotropic matter distribution in $f(\mathcal{R},\mathcal{T},\mathcal{Q})$ theory, where $\mathcal{Q}=\mathcal{R}_{ϕψ}\mathcal{T}^{ϕψ}$. For this purpose, we take a linear model of this gravity as $\mathcal{R}+ζ\mathcal{Q}$, where $ζ$ represents a coupling constant. We consider a self-gravitating spherical geometry in the presence of electromagnetic field and generate solution to the modified field equations by using the ``embedding class-one'' condition and $\mathbb{MIT}$ bag model equation of state. The observational data (masses and radii) of four different stellar models like 4U 1820-30,~SAX J 1808.4-3658,~SMC X-4 and Her X-I is employed to analyze the effects of charge on their physical properties. Finally, the effect of the coupling constant is checked on the viability, hydrostatic equilibrium condition and stability of the resulting solution. We conclude that the considered models show viable and stable behavior for all the considered values of charge and $ζ$.

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arXiv2023

Scalar Field Cosmology via Noether Symmetries in Energy-Momentum Squared Gravity

This article examines the analytic solutions of isotropic spacetime with the minimal coupling of scalar field and matter in the context of energy-momentum squared gravity. The scalar field includes quintessence and phantom dark energy models. We evaluate solutions of a physical system through the Noether symmetry approach that provide some viable constraints to choose the cosmological models on the basis of current observations. We consider different models of this theory to establish Noether equations, symmetry generators and corresponding conserved quantities. We compute analytic solutions and examine their graphical representation for various cosmological quantities. The behavior of these quantities is found to be consistent with current observations implying that this theory shows expanding behavior of the universe. We find that symmetry generators and their conserved parameters exist in all cases.

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arXiv2023

Complexity of Charged Dynamical Spherical System in Modified Gravity

In this paper, we consider the effect of electromagnetic field to the definition of complexity in the context of $f(G,T)$ gravity, where $G$ and $T$ express the Gauss-Bonnet term and energy-momentum tensor, respectively. The physical parameters such as anisotropic pressure, charge, energy density inhomogeneity, heat dissipation and correction terms are found responsible to induce complexity within the self-gravitating objects. The scalar functions are determined using Herrera's orthogonal splitting approach, which results in a complexity factor that includes all of the system's essential features. Furthermore, we investigate the dynamics of charged spherical distribution by choosing homologous mode as the simplest evolutionary pattern. Dissipative and non-dissipative cases associated with complexity free and homologous conditions are also discussed. Finally, we study the components responsible for producing complexity during the evolution process. We deduce that the inclusion of extra curvature terms and charge in $f(G, T)$ gravity enhances the complexity of the self-gravitating structure.

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arXiv2023

Charged Anisotropic Models with Complexity-free Condition

This paper uses the definition of complexity for a static spherically symmetric spacetime and extends it to the case of charged distribution. We formulate the Einstein-Maxwell field equations corresponding to the anisotropic interior and calculate two different mass functions. We then take Reissner-Nordström metric as an exterior spacetime to find the matching conditions at the spherical boundary. Some scalars are developed from the orthogonal splitting of the curvature tensor, and we call one of them, i.e., $\mathcal{Y}_{TF}$ as the complexity factor for the considered setup. Further, the three independent field equations are not enough to close the system, therefore, we adopt the complexity-free condition. Along with this condition, we consider three constraints that lead to different models. We also present the graphical interpretation of the resulting solutions by choosing some particular values of parameters. We conclude that the models corresponding to $p_r=0$ and a polytropic equation of state show viable and stable behavior everywhere.

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arXiv2023

Compact Objects admitting Finch-Skea Symmetry in $f(\mathcal{R},T^2)$ Gravity

This paper investigates the viability and stability of anisotropic compact stars in the framework of $f(\mathcal{R},\mathrm{T}^{2})$ theory ($\mathcal{R}$ is the Ricci scalar and $\mathrm{T}^{2}=\mathrm{T}_{τ\upsilon}\mathrm{T}^{τ\upsilon}$). In this perspective, we use Finch-Skea symmetry and consider different $f(\mathcal{R},\mathrm{T}^{2})$ models to examine physical characteristics of compact stars. We match interior spacetime with the exterior region to find the values of unknown constants. Further, we analyze the behavior of several physical quantities such as effective matter variables, energy bounds, anisotropic factor and equation of state parameters in the interior of Vela X-1, SAX J 1808.4-3658, Her X-1 and PSR J0348+0432 stars. The equilibrium state of these compact stars is examined through the Tolman-Oppenheimer-Volkoff equation and their stability is checked by causality condition, Herrera cracking approach and adiabatic index. It is found that all the required conditions are fulfilled for the considered models. We can conclude that more viable and stable compact stars are obtained in this modified theory.

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arXiv2023

Noether Symmetries and Anisotropic Universe in Energy-Momentum Squared Gravity

This paper explores exact cosmological solutions of anisotropic universe model through Noether symmetry technique in energy-momentum squared gravity. This theory resolves the primordial singularity and provides viable cosmological consequences in the early universe. We consider specific models of this theory and evaluate Noether equations, symmetry generators and corresponding conserved parameters. We then find exact solutions through conserved parameters and analyze their graphical behavior for different cosmological parameters. It is found that the behavior of these parameters is consistent with recent observations indicating that this theory supports current cosmic accelerated expansion. We conclude that conserved parameters are very helpful to obtain exact cosmological solutions.

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arXiv2023

Study of Decoupled Cosmological Solutions in $f(\mathbb{R},\mathbb{T})$ Theory

In this paper, we consider a non-static spherical geometry and formulate its extension for the case of anisotropic matter configuration through minimal gravitational decoupling in $f(\mathbb{R},\mathbb{T})$ theory. We apply a particular transformation only on the radial metric function that divides the modified field equations into two distinct sectors corresponding to their parent (original and additional) sources. The unknowns in the first (isotropic) set are reduced by taking the Friedmann-Lemaitre-Robertson-Walker cosmic model. We then obtain the isotropic solution by employing a linear equation of state and power-law form of the scale factor. The other set involves the decoupling function and components of an extra source, therefore we adopt a density-like constraint to close it. Finally, we analyze the role of this modified gravity and the decoupling parameter on three different eras of the cosmos by graphically observing the developed extended solution. It is concluded that the resulting solutions fulfill all the physical requirements only for the matter and radiation-dominated eras.

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arXiv2023

Traversable Wormhole Solutions admitting Noether Symmetry in $f(\mathcal{R,}\mathcal{T}^{2})$ Theory

This paper uses the Noether symmetry approach to examine the viable and stable traversable wormhole solutions in the framework of $f(\mathcal{R,}\mathcal{T}^{2})$ theory, where $\mathcal{R}$ is the Ricci scalar and $\mathcal{T}^{2}=\mathcal{T}_{μν}\mathcal{T}^{μν}$ is the self-contraction of stress-energy tensor. For this purpose, we consider a specific model of this modified theory to obtain exact solutions of the Noether equations. Further, we formulate the generators of Noether symmetry and first integrals of motion. We analyze the presence of viable and stable traversable wormhole solutions corresponding to different redshift functions. In order to determine whether this theory provides physically viable and stable wormhole geometry or not, we check the graphical behavior of null energy constraint, causality condition and adiabatic index for effective stress-energy tensor. It is found that viable and stable traversable wormhole solutions exist in this modified theory.

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arXiv2023

Study of Decoupled Gravastars in Energy-momentum Squared Gravity

In this paper, we generate an exact anisotropic gravastar model using gravitational decoupling technique through minimal geometric deformation in the framework of $f(\Re, {T}^{2})$ gravity. This novel model explains an ultra-compact stellar configuration whose internal region is smoothly matched to the exterior region. The developed stellar model satisfies some of the essential characteristics of a physically acceptable model such as a positive monotonically decreasing profile of energy density from the center to the boundary and monotonically decreasing behavior of the pressure. The anisotropic factor and Schwarzschild spacetime follows physically acceptable behavior. We find that all the energy bounds are satisfied except strong energy condition inside the ultra-compact stellar structure for the coupling constant of this theory, which is compatible with the regularity condition.

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arXiv2023

Effects of Non-minimal Matter-geometry Coupling on Embedding Class-one Anisotropic Solutions

This paper investigates some particular anisotropic star models in $f(\mathcal{R},\mathcal{T},\mathcal{Q})$ gravity, where $\mathcal{Q}=\mathcal{R}_{ωα}\mathcal{T}^{ωα}$. We adopt a standard model $f(\mathcal{R},\mathcal{T},\mathcal{Q})=\mathcal{R}+\varpi\mathcal{Q}$, where $\varpi$ indicates a coupling constant. We take spherically symmetric spacetime and develop solutions to the modified field equations corresponding to different choices of the matter Lagrangian by applying `embedding class-one' scheme. For this purpose, we utilize $\mathbb{MIT}$ bag model equation of state and investigate some physical aspects of compact models such as RXJ 1856-37,~4U 1820-30,~Cen X-3,~SAX J 1808.4-3658 and Her X-I. We use masses and radii of these stars and employ the vanishing radial pressure condition at the boundary to calculate the value of their respective bag constant $\mathfrak{B_c}$. Further, we fix $\varpi=\pm4$ to analyze the behavior of resulting state variables, anisotropy, mass, compactness, surface redshift as well as energy bounds through graphical interpretation for each star model. Two different physical tests are performed to check the stability of the developed solutions. We conclude that $\varpi=-4$ is more suitable choice for the considered modified model to obtain stable structures of the compact bodies.

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arXiv2023

Study of Charged Compact Stars in Non-minimally Coupled Gravity

This paper studies the structural formation of various spherically symmetric anisotropic configured stars in $f(\mathcal{R},\mathcal{T},\mathcal{Q})$ gravity under the influence of electromagnetic field, where $\mathcal{Q}=\mathcal{R}_{ησ}\mathcal{T}^{ησ}$. We construct modified field equations by adopting the Krori-Barua metric potentials (involving unknowns ($A,B,C$)) and employ bag model equation of state to explore the physical characteristics of compact structures like Vela X-I,~4U 1820-30,~SAX J 1808.4-3658,~Her X-I and RXJ 1856-37. The bag constant ($\mathfrak{B_c}$) and other three unknowns are calculated by using experimental data of all considered stars. Further, we adopt a standard model $\mathcal{R}+\varpi\mathcal{R}_{ησ}\mathcal{T}^{ησ}$ to interpret the graphical behavior of energy density, pressure in radial and tangential directions as well as anisotropy. We also investigate mass, compactness parameter, surface redshift and energy conditions for compact bodies by taking model parameter ($\varpi$) as $\pm5$. The stability of the obtained solution is examined by means of two different criteria. We conclude that our proposed solution meets all the physical requirements and shows stable behavior everywhere for $\varpi=5$.

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arXiv2023

Traversable Wormhole Solutions admitting Karmarkar Condition in $f(R,T)$ Theory

In this paper, we evaluate traversable wormhole solutions through Karmarkar condition in $f(R,T)$ theory, where $T$ is the trace of the energy-momentum tensor and $R$ represents the Ricci scalar. We develop a wormhole shape function for the static traversable wormhole geometry by using the embedding class-I technique. The resulting shape function is used to construct wormhole geometry that fulfills all the necessary conditions and joins the two asymptotically flat regions of the spacetime. We investigate the existence of viable traversable wormhole solutions for anisotropic matter configuration and examine the stable state of these solutions for different $f(R,T)$ gravity models. We analyze the graphical behavior of null energy bound to examine the presence of physically viable wormhole geometry. It is found that viable and stable traversable wormhole solutions exist in this modified theory of gravity.

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arXiv2023

Extended Decoupled Anisotropic Solutions in $f(\mathcal{R},\mathcal{T},\mathcal{R}_{γχ}\mathcal{T}^{γχ})$ Gravity

In this paper, we consider static spherical structure to develop some anisotropic solutions by employing the extended gravitational decoupling scheme in the background of $f(\mathcal{R},\mathcal{T},\mathcal{R}_{γχ}\mathcal{T}^{γχ})$ gravity, where $\mathcal{R}$ and $\mathcal{T}$ indicate the Ricci scalar and trace of the energy-momentum tensor, respectively. We transform both radial as well as temporal metric functions and apply them on the field equations that produce two different sets corresponding to the decoupling parameter $ξ$. The first set is associated with isotropic distribution, i.e., modified Krori-Barua solution. The second set is influenced from anisotropic factor and contains unknowns which are determined by taking some constraints. The impact of decoupling parameter is then analyzed on the obtained physical variables and anisotropy. We also investigate energy conditions and some other parameters such as mass, compactness and redshift graphically. It is found that our solution corresponding to pressure-like constraint shows stable behavior throughout in this gravity for the considered range of $ξ$.

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arXiv2023

Effect of Extended Gravitational Decoupling on Isotropization and Complexity in f(\mathbb{R},\mathbb{T}) Theory

This paper develops some new analytical solutions to the $f(\mathbb{R},\mathbb{T})$ field equations through extended gravitational decoupling. For this purpose, we take spherical anisotropic configuration as a seed source and extend it to an additional source. The modified field equations comprise the impact of both sources which are then decoupled into two distinct sets by applying the transformations on $g_{tt}$ and $g_{rr}$ metric potentials. The original anisotropic source is adorned by the first sector, and we make it solvable by considering two different well-behaved solutions. The second sector is in terms of an additional source and we adopt some constraints to find deformation functions. The first constraint is the isotropization condition which transforms the total fluid distribution into an isotropic system only for a specific value of the decoupling parameter. The other constraint is taken as the complexity-free fluid distribution. The unknown constants are calculated at the hypersurface through matching conditions. The preliminary information (mass and radius) of a compact star $4U 1820-30$ is employed to analyze physical attributes of the resulting models. We conclude that certain values of both the coupling as well as decoupling parameter yield viable and stable solutions in this theory.

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arXiv2023

Electromagnetic Effects on the Complexity of Static Cylindrical Object in $f(G,T)$ Gravity

In this paper, we investigate complexity of anisotropic cylindrical object under the influence of electromagnetic field in $f(G,T)$ theory, where $G$ and $T$ indicate the Gauss-Bonnet term and trace of the stress-energy tensor, respectively. For this purpose, we calculate the modified field equations, non-conservation equation and mass distributions that assist in comprehending the structure of astrophysical objects. The Riemann tensor is divided into different structure scalars, among which one is called the complexity factor. This factor is used to measure complexity of the system due to the involvement of inhomogeneous energy density, anisotropic pressure and charge. The vanishing of the complexity factor is employed as a constraint to formulate charged static solutions for the Gokhroo-Mehra model and polytropic equation of state. We conclude that the presence of charge reduces the complexity of the anisotropic system.

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arXiv2022

Noether Symmetries and Some Exact Solutions in $f(R, T^{2})$ Theory

The main objective of this article is to examine some physically viable solutions through the Noether symmetry technique in $f(R, T^{2})$ theory. For this purpose, we assume a generalized anisotropic and homogenous spacetime that yields distinct cosmic models. In order to investigate Noether equations, symmetry generators and conserved quantities, we use a specific model of this modified theory. We find exact solutions and examine the behavior of various cosmological quantities. It is found the behavior these quantities is consistent with current observations indicating that this theory describes the cosmic accelerated expansion. We conclude that generators of Noether symmetry and conserved quantities exist in this theory.

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arXiv2022

Isotropization and Complexity Analysis of Decoupled Solutions in $f(\mathbb{R},\mathbb{T})$ Theory

This paper formulates some new exact solutions to the field equations by means of minimal gravitational decoupling in the context of $f(\mathbb{R},\mathbb{T})$ gravity. For this purpose, we consider anisotropic spherical matter distribution and add an extra source to extend the existing solutions. We apply the transformation only on the radial metric potential that results in two different sets of the modified field equations, each of them corresponding to their parent source. The initial anisotropic source is represented by the first set, and we consider two different well-behaved solutions to close that system. On the other hand, we impose constraints on the additional source to make the second set solvable. We, firstly, employ the isotropization condition which leads to an isotropic system for a particular value of the decoupling parameter. We then use the condition of zero complexity of the total configuration to obtain the other solution. The unknowns are determined by smoothly matching the interior and exterior spacetimes at the hypersurface. The physical viability and stability of the obtained solutions is analyzed by using the mass and radius of a compact star $4U 1820-30$. It is concluded that both of our extended solutions meet all the physical requirements for considered values of the coupling/decoupling parameters.

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arXiv2022

Influence of Charge on Decoupled Anisotropic Spheres in $f(G,T)$ Gravity

In this paper, we develop two anisotropic solutions for static self-gravitating spherical structure in the presence of electromagnetic field through gravitational decoupling approach in $f(G,T)$ theory, where $G$ and $T$ denote the Gauss-Bonnet term and trace of the energy-momentum tensor, respectively. The extra source with isotropic seed sector is responsible for generating anisotropy in the spacetime. The system of field equations is decoupled into two arrays by using minimal geometric deformation in the radial component. The first set portrays the isotropic regime whereas the second set represents the anisotropic system. The metric coefficients of the Krori-Barua spacetime are employed to extract solution of the first set while two constraints on the radial and temporal components of the extra source yield the corresponding two solutions. Finally, we investigate the influence of charge and decoupling parameter on the physical viability and stability of the obtained solutions. We conclude that the resulting solutions in this modified theory indicate more feasible and stable structures.

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