arXiv subjects

M. Sharif

Publications and source records attributed to M. Sharif.

At least 109 records · Page 6Linked to original sources

arXiv2022

Complexity Factor for Static Cylindrical System in Energy-momentum Squared Gravity

This paper investigates some physical features that give rise to complexity within the self-gravitating static cylindrical structure coupled with anisotropic distribution in the energy-momentum squared gravity. To accomplish this, we formulate the modified field equations and explore the structure of the astronomical body. The C-energy and Tolman mass are also calculated to discuss the matter distribution. We then obtain some structure scalars via orthogonal splitting of the Riemann tensor. Since, the complexity of the considered structure is influenced by a variety of variables, including anisotropic pressure and inhomogeneous energy density, etc. thus, we adopt the factor $\mathcal{Y}_{TF}$ as the complexity factor. Further, the complexity-free condition along with the Gokhroo-Mehra model and polytropic equation of state are taken to generate their corresponding solutions. We deduce that the inclusion of additional terms of this modified theory leads to a more complicated system.

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arXiv2022

Complexity Analysis of Charged Dynamical Dissipative Cylindrical Structure in Modified Gravity

This article focuses on the formulation of some scalar factors which are uniquely expressed in terms of matter variables for dynamical charged dissipative cylindrical geometry in a standard gravity model $\mathcal{R}+Φ\mathcal{Q}$ ($Φ$ is the coupling parameter, $\mathcal{Q}=\mathcal{R}_{φ\vartheta}\mathcal{T}^{φ\vartheta}$) and calculates four scalars by orthogonally decomposing the Riemann tensor. We find that only $\mathcal{Y}_{TF}$ involves inhomogeneous energy density, heat flux, charge and pressure anisotropy coupled with modified corrections, and thus call it as complexity factor for the considered distribution. Two evolutionary modes are discussed to study the dynamics of cylinder. We then take the homologous condition with $\mathcal{Y}_{TF}=0$ to calculate unknown metric potentials in the absence as well as presence of heat dissipation. The stability criterion of the later condition is also checked throughout the evolution by applying some constraints. We conclude that the effects of charge and modified theory yield more complex system.

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arXiv2022

Impact of Charge on Gravastars in $f(\mathfrak{R},\mathcal{T}^{2})$ Gravity

This paper studies the influence of charge on a compact stellar structure also regarded as vacuum condensate star in the background of $f(\mathfrak{R},\mathcal{T}^{2})$ gravity. This object is considered the alternate of black hole whose structure involves three distinct regions, i.e., interior, exterior and thin-shell. We analyze these domains of a gravastar for a particular model of this modified theory. In the inner region of a gravastar, the considered equation of state defines that energy density is equal to negative pressure which is the cause of repulsive force on the spherical shell. In the intermediate shell, pressure and energy density are equal and contain ultra-relativistic fluid. The inward-directed gravitational pull of thin-shell counterbalance the force exerted by the inner region of a gravastar allowing the formation of a singularity-free object. The Reissner-Nordstrom metric presents the outer vacuum spherical domain. Moreover, we discuss the impact of the charge on physical attributes of a gravastar such as the equation of state parameter, entropy, proper length and energy. We conclude that singularity-free solutions of charged gravastar are physically consistent in this modified theory.

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arXiv2022

Anisotropic Tolman V Solutions by Decoupling Approach in $f(R,T^{2})$ Gravity

This paper investigates the behavior of anisotropic static spheres that are constructed by employing a minimal geometric deformation in the framework of $f(R,T^{2})$ gravity ($T^{2}=T_{ζν}T^{ζν}$, $R$ is the Ricci scalar and $T_{ζν}$ is the energy-momentum tensor). We consider a spherical setup with two sources: seed and additional. It is assumed that the seed source is isotropic whereas the new source is responsible for inducing anisotropy. We deform the $g_{rr}$ component to split the field equations into two sets. The first array corresponds to the isotropic solution whereas the second set contains the effect of the anisotropic source. The system related to isotropic source is determined by the metric potentials of Tolman V solution while three solutions of the second set are constructed corresponding to three different constraints. The physical acceptability of all solutions is checked through energy conditions by employing the radius and mass of PSR J1614-2230 star. We also examine the stability, mass, compactness and redshift of the obtained solutions. We conclude that first two solutions satisfy the viability and stability criteria only for small values of the decoupling parameter while third solution is stable for its all possible values.

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arXiv2022

Greybody Factor for a Static Spherically Symmetric Black Hole With Non-Linear Electrodynamics

In this paper, we study the greybody factor for static spherically symmetric black hole with non-linear electrodynamics. For this purpose, we assume minimal coupling of the scalar field and find the radial equation by using the Klein-Gordon equation. We then apply tortoise coordinate to convert this equation into Schrodinger wave equation which helps to find the effective potential. The behavior of effective potential is checked for different values of the coupling and charge parameters. We find two solutions in two horizons named as event and cosmological horizons by using the radial equation. We consider the intermediate regime and match these two solutions to obtain the greybody factor and examine its behavior graphically. It is found that the greybody factor has an inverse relation with the coupling constant, mass, charge as well as the radius of the black hole and has a direct relation with angular momentum.

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arXiv2022

Impact of Charge on the Complexity of Static Sphere in $f(R,\textbf{T}^{2})$ Gravity

This paper investigates the complexity of a charged static sphere filled with anisotropic matter in the background of energy-momentum squared gravity. For this purpose, we evaluate the modified field and conservation equations to determine the structure of celestial system. The mass function is calculated through Misner-Sharp as well as Tolman mass definitions. The complexity of a self-gravitating system depends on different factors such as anisotropic pressure, electromagnetic field, energy density inhomogeneity, etc. We formulate the structure scalars by the orthogonal decomposition of the Riemann tensor to develop a complexity factor containing all vital features of the stellar structure. The vanishing complexity condition is achieved by setting the complexity factor equal to zero. Finally, we construct two static solutions by utilizing the energy density of Gokhroo-Mehra solution as well as the polytropic equation of state along with the zero complexity condition. It is found that electromagnetic field decreases the complexity of stellar structure.

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arXiv2022

Stable Charged Gravastar Model in ${f}(\mathfrak{R},\textbf{T}^{2})$ Gravity with Conformal Motion

This paper investigates the influence of charge on physical features of gravastars in the framework of energy-momentum squared gravity. A gravastar is an alternate model to a black hole that comprises of three distinct regions, namely the intermediate shell, inner and outer sectors. Different values of the barotropic equation of state parameter provide the mathematical formulation for these regions. We construct the structure of a gravastar admitting conformal motion for a specific model of energy-momentum squared gravity. The field equations are formulated for a spherically symmetric spacetime with charged perfect matter distribution. For the smooth matching of external and internal spacetimes, we use Israel matching criteria. Various physical attributes of gravastars such as the equation of state parameter, proper length, entropy and energy are investigated (in the presence of charge) versus thickness of the shell. The charge in the inner core of gravastars preserves the state of equilibrium by counterbalancing the inward gravitational force. It is concluded that the non-singular solutions of charged gravastar are physically viable in the background of energy-momentum squared gravity.

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arXiv2022

Study of Anisotropic Polytropes in $f(\mathcal{R},\mathrm{T})$ Theory

This paper examines the general formalism and applications of isotropic as well as anisotropic polytropic stars in curvature-matter coupled gravity. For this purpose, we consider static spherical and Schwarzschild spacetimes in the interior and exterior regions, respectively. We use two polytropic equations of state to obtain physically viable solutions of the field equations. The hydrostatic equilibrium and Lane-Emden equations are developed for both isotropic as well as anisotropic cases. We study the effects of anisotropic pressure on the stellar structure. Moreover, we graphically inspect the physical behavior of isotropic as well as anisotropic polytropes through energy conditions and stability criterion. Finally, we discuss Tolman mass to explore some characteristics of the models. It is concluded that more viable and stable polytropes are found in this theory as compared to general relativity.

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arXiv2022

Isotropization and Complexity of Decoupled Solutions in Self-interacting Brans-Dicke Gravity

The aim of this work is to formulate two new solutions by decoupling the field equations via a minimal geometric deformation in the context of self-interacting Brans-Dicke gravity. We introduce an extra source in the anisotropic fluid distribution to generate new analogs of existing solutions. The radial metric function is transformed to decouple the field equations into two sets such that each array corresponds to one source only. The system corresponding to the original matter distribution is specified by metric functions of well-behaved solutions. On the other hand, the second set is closed by imposing constraints on the additional matter source. For this purpose, we have applied the isotropization condition as well as vanishing complexity condition on the new source. Smooth matching of interior and exterior spacetimes at the junction provides values of the unknown constants. Interesting physical features of corresponding models are checked by employing the mass and radius of the star PSR J1614-2230. It is concluded that both extensions yield viable and stable models for certain values of the decoupling parameter.

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arXiv2021

Greybody Factor for a Rotating Bardeen Black Hole by Perfect Fluid Dark Matter

In this paper, the greybody factor is studied analytically for a rotating regular Bardeen black hole surrounded by perfect fluid dark matter. Firstly, we examine the behavior of effective potential by using the radial equation of motion developed from the Klein-Gordon equation. We then consider tortoise coordinate to convert the radial equation into Schrödinger form equation. We solve the radial equation of motion and obtain two different asymptotic solutions in terms of hypergeometric function measured at distinct regimes so called near and far-field horizons. These solutions are smoothly matched over the whole radial coordinate in an intermediate regime to check their viability. Finally, we measure the absorption probability for massless scalar field and examine the effect of perfect fluid dark matter. It is concluded that both the effective potential and greybody factor increase with perfect fluid dark matter.

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arXiv2021

Complexity for Dynamical Anisotropic Sphere in f(G,T) Gravity

This paper is devoted to the formulation of a complexity factor for dynamical anisotropic sphere in the framework of $f(G,T)$ gravity, where $G$ is the Gauss-Bonnet invariant and $T$ is the trace of energy-momentum tensor. Inhomogeneous energy density, anisotropic pressure, heat dissipation and modified terms create complexity within the self-gravitating system. We evaluate the structure scalars by orthogonal splitting of the Riemann tensor to evaluate a complexity factor which incorporates all the fundamental properties of the system. Moreover, we examine the dynamics of the sphere by assuming homologous mode as the simplest pattern of evolution. We also discuss dissipative as well as non-dissipative scenarios corresponding to homologous and complexity free conditions. Finally, we establish a criterion under which the complexity free condition remains stable throughout the process of evolution. We conclude that the presence of dark source terms of $f(G,T)$ gravity increase the system's complexity.

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arXiv2021

Stable Bounded Excursion Gravastars with Regular Black Holes

This paper explores the possible existence of stable regions of bounded excursion gravastars in the background of regular black holes (Bardeen and Bardeen-de Sitter black holes). For this purpose, we match internal de Sitter geometry with an external regular black hole through an intermediate shell with an equation of state. The matter surface located at the shell greatly affects the dynamical configuration of the shell. We consider stiff and dust fluids to discuss the outcomes of the developed structures. We then determine the critical values of physical parameters at which the shell neither collapses nor expands for both cases with different choices of external and internal geometries. It is found that there does not exist any possible region of stable bounded excursion gravastar for the interior flat and exterior regular geometries. However, the stable bounded excursion gravastar is obtained for the interior de Sitter and exterior regular black holes with a suitable choice of physical parameters for both stiff and dust shells. We conclude that the possibility of the existence of both bounded excursion gravastars as well as black holes cannot be excluded in the dynamical model.

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arXiv2021

Stability of $d$-dimensional Gravastars with Variable Equation of State

In this paper, we are interested to explore stable configurations of $d$-dimensional gravastars constructed from the interior $d$-dimensional de Sitter and exterior $d$-dimensional Schwarzschild/Reissner-Nordström (de Sitter) black holes through cut and paste approach. We consider the linearized radial perturbation preserving the original symmetries to explore their stability by using three different types of matter distributions. The resulting frameworks represent unstable structures for barotropic, Chaplygin, and phantomlike models for every considered choice of exterior geometries. However, matter contents with variable equations of state have a remarkable role to maintain the stability of gravastars. We conclude that stable structures of gravastars are obtained only for generalized variable models with exterior $d$-dimensional Schwarzschild/Reissner-Nordström-de Sitter black holes.

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arXiv2021

Effects of Non-linear Electrodynamics on Thermodynamics of Charged Black Hole

This paper investigates thermodynamics, quasi-normal modes, thermal fluctuations and phase transitions of Reissner-Nordström black hole with the effects of non-linear electrodynamics. We first compute the expressions for Hawking temperature, entropy and heat capacity of this black hole and then obtain a relation between Davies's point and quasi-normal modes with non-linear electrodynamics. We also observe the effects of logarithmic corrections on uncorrected thermodynamic quantities such as entropy, Hawking temperature, Helmholtz free energy, internal energy, Gibbs free energy, enthalpy and heat capacity. It is found that presence of non-linear electrodynamic parameter induces more instability in black holes of large radii. Finally, we analyze the phase transitions of Hawking temperature as well as heat capacity in terms of entropy for different values of charge ($q$), horizon radius ($r_{+}$) and coupling parameter ($α$). We obtain that Hawking temperature changes its phase from positive to negative for increasing values of $q$ and $r_{+}$ while it shows opposite trend for higher values of $α$. The heat capacity changes its phase from negative to positive for large values of charge, horizon radius and coupling parameter.

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arXiv2021

Stability of the Closed Einstein Universe in Energy-Momentum Squared Gravity

This paper analyzes the stability of the closed Einstein static universe by using linear homogeneous perturbations in the framework of energy-momentum squared gravity. This newly developed proposal resolves the primordial singularity and yields feasible cosmological results in the early times. For this purpose, we consider the closed Friedmann-Robertson-Walker universe with isotropic matter configuration and adopt small perturbations on the matter parameters and scale factor. Further, we establish equations of motion for static as well as perturbed systems and analyze the stable regions for particular $f(\mathcal{R},\mathbf{T}^{2})$ models corresponding to both conserved and non-conserved energy-momentum tensor. The graphical interpretation demonstrates that stable regions of the Einstein cosmos exist for all values of the model parameters and equation of state variable. We conclude that stable regions in this modified theory are large as compared to other modified theories of gravity.

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arXiv2021

Compact Objects by Gravitational Decoupling in f(R) Gravity

The objective of this paper is to discuss anisotropic solutions representing static spherical self-gravitating systems in $f(R)$ theory. We employ the extended gravitational decoupling approach and transform temporal as well as radial metric potentials which decomposes the system of non-linear field equations into two arrays: one set corresponding to seed source and the other one involves additional source terms. The domain of the isotropic solution is extended in the background of $f(R)$ Starobinsky model by employing the metric potentials of Krori-Barua spacetime. We determine two anisotropic solutions by employing some physical constraints on the extra source. The values of unknown constants are computed by matching the interior and exterior spacetimes. We inspect the physical viability, equilibrium and stability of the obtained solutions corresponding to the star Her X-I. It is observed that one of the two extensions satisfies all the necessary physical requirements for particular values of the decoupling parameter.

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arXiv2021

Complexity Analysis of Dynamical Cylinder in Massive Brans-Dicke Gravity

In this paper, a complexity factor is devised for a non-static cylindrical system in the framework of massive Brans-Dicke theory. The definition of complexity is developed by taking into account the essential physical characteristics (such as anisotropy, inhomogeneity, etc.) of the system. In order to determine the complexity factor of the self-gravitating object, we acquire structure scalars from the orthogonal splitting of the Riemann tensor. Moreover, we discuss two patterns of evolution and choose the homologous mode as the simplest pattern under the influence of massive scalar field. We derive solutions in the absence as well as presence of heat dissipation for a specific form of the scalar field. The factors that induce complexity in an initially complexity-free system are also examined. It is concluded that the massive scalar field as well as heat dissipation contribute to the complexity of the celestial system. Thus, a dynamical cylinder is more complex as compared to its static counterpart.

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arXiv2021

Viable Wormhole Solutions in Energy-Momentum Squared Gravity

This paper investigates static wormhole solutions through Noether symmetry approach in the context of energy-momentum squared gravity. This newly developed proposal resolves the singularity of big-bang and yields feasible cosmological results in the early times. We consider the particular model of this theory to establish symmetry generators and corresponding conserved quantities. For constant and variable red-shift functions, we examine the presence of viable traversable wormhole solutions for both dust as well as non-dust matter distributions and analyze the stable state of these solutions. We investigate the graphical interpretation of null and weak energy bounds for normal and effective energy-momentum tensors to examine the presence of physically viable wormhole geometry. It is found that realistic traversable and stable wormhole solutions are obtained for a particular model of this gravity.

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