arXiv subjects

M. Sharif

Publications and source records attributed to M. Sharif.

At least 55 records · Page 3Linked to original sources

arXiv2024

Stability Analysis of Static Spherical Spacetime in Extended Symmetric Teleparallel Gravity

Our manuscript aims to analysis the viability and stability of anisotropic stellar objects in the modified symmetric teleparallel gravity. A particular model of this extended theory is considered to formulate explicit field equations which govern the interaction between matter and geometry. The configuration of static spherical symmetric structures is examined through the Finch-Skea solution. However, the values of unknown constants in the metric potentials are evaluated by the Darmois junction conditions. For the viability of proposed stellar objects, the physical parameters including density, pressure, anisotropy, mass, energy constraints, compactness function and redshift are analyzed. Furthermore, stability of the proposed stellar objects is investigated by causality condition, Herrera cracking approach and adiabatic index. Our findings indicate that the proposed stellar objects are viable as well as stable in the presence of correction terms.

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arXiv2024

Pilgrim and Generalized Ghost Pilgrim Dark Energy Models in Modified Symmetric Teleparallel Gravity

In this paper, we investigate $f(Q)$ gravity ($Q$ represents the non-metricity) to explore its cosmological implications of the two non-interacting dark energy models. We use the correspondence scenario to find the pilgrim and generalized ghost pilgrim dark energy $f(Q)$ gravity models for a Friedmann-Robertson-Walker universe with pressureless matter and a power-law scale factor. The reconstructed models explain the observed rapid expansion of the universe using astronomical observations. We also examine the physical properties of the model, including its equation of state parameter, $(ω_{D}-ω^{\prime}_{D})$ and $(r-s)$-planes and the squared speed of sound. It is found that our results are consistent with the interacting pilgrim dark energy model in the same gravity.

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arXiv2024

Decoupled Anisotropic Buchdahl's Relativistic Models in $f(\mathbb{R},\mathbb{T})$ Theory

This paper constructs three different anisotropic extensions of the existing isotropic solution to the modified field equations through the gravitational decoupling in $f(\mathbb{R},\mathbb{T})$ theory. For this, we take a static sphere that is initially filled with the isotropic fluid and then add a new gravitational source producing anisotropy in the system. The field equations now correspond to the total matter configuration. We transform the radial metric component to split these equations into two sets characterizing their parent sources. The unknowns comprising in the first set are determined by considering the Buchdahl isotropic solution. On the other hand, we employ different constraints related to the additional gravitational source and make the second system solvable. Further, the constant triplet in Buchdahl solution is calculated by means of matching criteria between the interior and exterior geometries at the spherical boundary. The mass and radius of a compact star LMC X-4 are used to analyze the physical relevancy of the developed models. We conclude that our resulting models II and III are in well-agreement with acceptability conditions for the considered values of the parameters.

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arXiv2024

Comprehensive Study of Bouncing Cosmological Models in $f(Q,T)$ Theory

The main objective of this article is to investigate the viability of bouncing cosmological scenarios using different forms of scale factors with perfect matter configuration in the framework of extended symmetric teleparallel theory. This modified proposal is defined by the function $f(Q,T)$, where $Q$ characterizes non-metricity and $T$ denotes the trace of energy-momentum tensor. We investigate the modified field equations of this theory using different parametric values of the Hubble parameter and non-metricity to derive viable solutions. These solutions are relevant in various cosmological bounce models such as symmetric-bounce, super-bounce, oscillatory-bounce, matter-bounce and exponential-bounce models. Furthermore, we examine the behavior of energy density and pressure to analyze the characteristics of dark energy. A comprehensive analysis is also conducted to explore the behavior of the equation of state parameter and deceleration parameter to examine the evolutionary eras of the cosmos. Our findings show that the $f(Q,T)$ gravity describes the cosmic expansion in the vicinity of the bouncing point during the early and late times of cosmic evolution.

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arXiv2024

Physical Analysis of Spherical Stellar Structures in $f(\mathrm{Q},\mathrm{T})$ Theory

This paper explores the viability and stability of compact stellar objects characterized by anisotropic matter in the framework of $f(\mathrm{Q},\mathrm{T})$ theory, where $\mathrm{Q}$ denotes non-metricity and $\mathrm{T}$ represents the trace of the energy-momentum tensor. We consider a specific model of this theory to obtain explicit expressions for the field equations governing the behavior of matter and geometry in this context. Furthermore, the Karmarkar condition is employed to assess the configuration of static spherically symmetric structures. The values of unknown constants in the metric potentials are determined through matching conditions of the interior and exterior spacetimes. Various physical quantities such as fluid parameters, energy constraints, equation of state parameters, mass, compactness and redshift are graphically analyzed to evaluate the viability of the considered compact stars. The Tolman-Oppenheimer-Volkoff equation is used to examine the equilibrium state of the stellar models. Moreover, the stability of the proposed compact stars is investigated through sound speed and adiabatic index methods. This study concludes that the proposed compact stars analyzed in this theoretical framework are viable and stable, as all the required conditions are satisfied.

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arXiv2024

Study of Anisotropic Compact Stars in $f(\mathcal{R},\mathcal{T},\mathcal{R}_{χξ}\mathcal{T}^{χξ})$ Gravity

This paper aims to examine the composition of various spherically symmetric star models which are coupled with anisotropic configuration in $f(\mathcal{R},\mathcal{T},\mathcal{Q})$ gravity, where $\mathcal{Q}=\mathcal{R}_{χξ}\mathcal{T}^{χξ}$. We discuss the physical features of compact objects by employing bag model equation of state and construct the modified field equations in terms of Krori-Barua ansatz involving unknowns ($A,B,C$). The observational data of 4U 1820-30,~Vela X-I,~SAX J 1808.4-3658,~RXJ 1856-37 and Her X-I is used to calculate these unknowns and bag constant $\mathfrak{B_c}$. Further, we observe the behavior of energy density, radial and tangential pressure as well as anisotropy through graphical interpretation for a viable model $\mathcal{R}+\varrho\mathcal{Q}$ of this gravity. For a particular value of the coupling constant $\varrho$, we study the behavior of mass, compactness, redshift and the energy bounds. The stability of the considered stars is also checked by using two criteria. We conclude that our developed structure in this gravity is in well-agreement with all the physical requirements.

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arXiv2024

Cosmic Expansion and Noether Gauge Symmetries in $f(R,T,R_{μν}T^{μν})$ Gravity

The present work explores different evolutionary phases of isotropically homogeneous and flat cosmos filled with dust fluid in non-minimally coupled gravity. We consider different models of this gravity to discuss the presence of symmetry generators together with conserved integrals using Nother Gauge symmetry scheme. In most of the cases, we obtain temporal and scaling symmetries that yield conservation of energy and linear momentum, respectively. In the absence of contracted Ricci and energy-momentum tensors, we obtain maximum symmetries but none of them correspond to any standard symmetry or conservation law. We formulate exact solutions and construct graphical analysis of standard cosmological parameters. We observe realistic nature of new models via squared speed of sound, viability conditions suggested by Dolgov-Kawasaki instability and state-finder parameters. We investigate the behavior of fractional densities and check the compatibility with Planck 2018 observational data. The new models are stable and viable preserving compatibility with $Λ$CDM and Chaplygin gas models. It is concluded that most of the solutions favor accelerated cosmic expansion.

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arXiv2024

Anisotropic Durgapal-Fuloria Neutron Stars in $f(\mathcal{R},\mathrm{T}^{2})$ Gravity

The main purpose of this paper is to obtain physically stable stellar models coupled with anisotropic matter distribution in the context of $f(\mathcal{R},\mathrm{T}^{2})$ theory. For this, we consider a static spherical geometry and formulate modified field equations containing various unknowns such as matter determinants and metric potentials. We then obtain a unique solution to these equations by employing Durgapal-Fuloria ansatz possessing a constant doublet. We also use matching criteria to calculate the values of these constants by considering the Schwarzschild exterior spacetime. Two different viable models of this modified theory are adopted to analyze the behavior of effective matter variables, anisotropy, energy conditions, compactness and redshift in the interiors of Her X-1, PSR J0348-0432, LMC X-4, SMC X-1, Cen X-3, and SAX J 1808.4-3658 star candidates. We also check the stability of these models by using three different physical tests. It is concluded that our considered stars satisfy all the physical requirements and are stable in this modified gravity for the considered parametric values.

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arXiv2024

Compact Objects by Extended Gravitational Decoupling in f(G,T) Gravity

In this paper, we investigate the anisotropic interior spherically symmetric solutions by utilizing the extended gravitational decoupling method in the background of $f(G,T)$ gravity, where $G$ and $T$ signify the Gauss-Bonnet term and trace of the stress-energy tensor, respectively. The anisotropy in the interior geometry arises with the inclusion of an additional source in the isotropic configuration. In this technique, the temporal and radial potentials are decoupled which split the field equations into two independent sets. Both sets individually represent the isotropic and anisotropic configurations, respectively. The solution corresponding to the first set is determined by using the Krori-Barua metric potentials whereas the second set contains unknown which are solved with the help of some constraints. The ultimate anisotropic results are evaluated by combining the solutions of both distributions. The influence of decoupling parameter is examined on the matter variables as well as anisotropic factor. We illustrate the viable and stable features of the constructed solutions by using energy constraints and three stability criteria, respectively. Finally, we conclude that the obtained solutions are viable as well as stable for the whole domain of the coupling parameter.

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arXiv2024

Analysis of Reconstructed Modified f(Q,T) Gravity

This paper studies the reconstruction criterion in the framework of $f(Q,T)$ gravity using ghost dark energy model, where $Q$ represents the non-metricity and $T$ is the trace of energy-momentum tensor. In this regard, the correspondence scenario for a non-interacting scheme is used to construct the ghost dark energy $f(Q,T)$ model. We consider the flat Friedmann-Robertson-Walker universe with power-law scale factor and pressure-less matter. We investigate the behavior of equation of state parameter and examine the stability of ghost dark energy model via squared speed of sound parameter. The equation of state parameter depicts the phantom era, while the squared speed of sound reveals stable ghost dark energy model for the entire cosmic evolutionary paradigm. Finally, we study the cosmography of the $ω_{GDE}-ω'_{GDE}$ and $r-s$ planes that correspond to freezing region and Chaplygin gas model, respectively. It is concluded that the reconstructed ghost dark energy model represents the evolution of the cosmos for suitable choices of the parametric values.

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arXiv2024

Study of Charged Cylindrical Collapse in $f(\mathcal{R},\mathcal{T},\mathcal{Q})$ Gravity

This paper investigates the effects of electromagnetic field on the gravitational collapse in $f(\mathcal{R},\mathcal{T},\mathcal{Q})$ theory, where $\mathcal{Q} = \mathcal{R}_{φ\vartheta} \mathcal{T}^{φ\vartheta}$. For this, we assume dynamical cylindrically symmetric self-gravitating geometry which is coupled with generalized anisotropic matter distribution as well as dissipation flux. We adopt the model $\mathcal{R}+Φ\sqrt{\mathcal{T}}+Ψ\mathcal{Q}$ to formulate the corresponding dynamical and transport equations by employing the Misner-Sharp as well as Müler-Israel Stewart formalisms, where $Φ$ and $Ψ$ are real-valued coupling constants. The influence of state variables, heat dissipation, charge and the bulk viscosity on the collapsing phenomenon is then studied by establishing some relations between these evolution equations. Moreover, the Weyl scalar and the modified field equations are expressed in terms of each other. We apply some constraints on the considered modified model and the fluid configuration to obtain conformally flat spacetime. Finally, we address different cases to check how the modified corrections and charge affect the collapse rate of cylindrical matter source.

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arXiv2024

Spherically Symmetric Wormhole Solutions admitting Karmarkar Condition

This paper investigated the viable traversable wormhole solutions through Karmarkar condition in the context of $f(\mathcal{G},T)$ theory. A static spherical spacetime with anisotropic matter configuration is used to study the wormhole geometry. Karmarkar condition is used to develop a viable shape function for a static wormhole structure. A wormhole geometry is constructed using the resulting shape function that satisfies all the required conditions and connects the asymptotically flat regions of the spacetime. To assess the viability of traversable wormhole geometries, the energy conditions are analyzed by various models of this theory. Further, their stable state is investigated through sound speed and adiabatic index. This investigation demonstrates the presence of viable traversable wormhole solutions in the modified theory.

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arXiv2024

Study of Decoupled Anisotropic Solutions in $f(R,T,R_{ρη}T^{ρη})$ Theory

In this paper, we consider isotropic solution and extend it to two different exact well-behaved spherical anisotropic solutions through minimal geometric deformation method in $f(R,T,R_{ρη}T^{ρη})$ gravity. We only deform the radial metric component that separates the field equations into two sets corresponding to their original sources. The first set corresponds to perfect matter distribution while the other set exhibits the effects of additional source, i.e., anisotropy. The isotropic system is resolved by assuming the metric potentials proposed by Krori-Barua while the second set needs one constraint to be solved. The physical acceptability and consistency of the obtained solutions are analyzed through graphical analysis of effective matter components and energy bounds. We also examine mass, surface redshift and compactness of the resulting solutions. For particular values of the decoupling parameter, our both solutions turn out to be viable and stable. We conclude that this curvature-matter coupling gravity provides more stable solutions corresponding to a self-gravitating geometry.

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arXiv2024

Analysis of Bouncing Cosmology in Non-Riemannian Geometry

The main objective of this manuscript is to investigate the bouncing cosmology in the background of $f(\mathcal{Q})$ gravity, where $\mathcal{Q}$ defines the non-metricity. For this purpose, we use the reconstruction approach and consider a flat Friedmann-Robertson-Walker spacetime with perfect matter configuration. We examine how the first contracting phase gives the expansion by using a temporal derivative of the scale factor, i.e., $\dot{a}<0$, $\dot{a}=0$ and $\dot{a}>0$ give contraction, bounce point and expansion phases, respectively. Further, we use the order reduction method to solve the modified field equations as these are very difficult due to the presence of additional non-linear expressions. It is analyzed that the original singularity of the universe diminishes for the required bounce conditions. We conclude that the acceleration occurs near the bouncing point and the considered $f(\mathcal{Q})$ models are consistent with the current cosmic accelerated expansion.

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arXiv2024

Study of Viable Compact Stellar Structures in Non-Riemannian Geometry

The main objective of this article is to study the viable compact stellar structures in non-Riemannian geometry, i.e., $f(\mathbb{Q},T)$ theory, where $\mathbb{Q}$ defines the non-metricity and $T$ represents trace of the stress-energy tensor. In this perspective, we consider a static spherical metric with anisotropic matter configuration to examine the geometry of considered compact stars. A specific model of this theory is used to derive the explicit expressions of energy density and pressure components that govern the relationship between matter and geometry. The unknown parameters are evaluated by using the continuity of inner and outer spacetimes to examine the configuration of spherical stellar structures. Physical parameters such as fluid characteristics, energy constraints and equation of state parameters are analyzed to examine the viability of the considered stellar objects. Further, we use Tolman-Oppenheimer-Volkoff equation, sound speed and adiabatic index methods to analyze the equilibrium state and stability of the proposed stellar objects. The rigorous analysis and satisfaction of necessary conditions lead to the conclusion that the stellar objects studied in this framework are viable and stable.

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arXiv2024

Generalized Ghost Dark Energy in f(Q) Gravity

In this manuscript, we use the correspondence principle to construct the generalized ghost dark energy $f(Q)$ model, where $Q$ is the non-metricity. For this purpose, we use the Friedman-Robertson-Walker universe model with power-law scale factor. The energy density in this model linearly depends on the Hubble parameter, with a sub-leading term of $H^{2}$, resulting in an energy density $ρ_D=ξH+ζH^{2}$, where $ξ$ and $ζ$ are arbitrary constants. We reconstruct interacting fluid scenario of this dark energy with dark matter. The reformulated $f(Q)$ gravity model shows how different epochs of the cosmic history can be reproduced by this modified gravity model. The physical characteristics of the model are discussed through the equation of state parameter with the planes of $ω_{D}-ω'_{D}$ and $r-s$. We also explore the stability criteria for the interacting model using the squared speed of sound. The equation of state parameter indicates phantom phase of the universe and the squared speed of sound represents stability of the interacting model. The $(ω_{D}-ω^{\prime}_{D})$-plane indicates freezing region, while the $(r-s)$-plane corresponds to the Chaplygin gas. We conclude that our findings coincide with the latest observational data.

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arXiv2024

Effects of $f(\mathcal{R},\mathcal{T},\mathcal{R}_{γ\upsilon}\mathcal{T}^{γ\upsilon})$ Gravity on Anisotropic Charged Compact Structures

This paper focuses on the analysis of static spherically symmetric anisotropic solutions in the presence of electromagnetic field through the gravitational decoupling approach in $f(\mathcal{R},\mathcal{T},\mathcal{R}_{γ\upsilon}\mathcal{T}^{γ\upsilon})$ gravity. We use geometric deformation only on radial metric function and obtain two sets of the field equations. The first set deals with isotropic fluid while the second set yields the influence of anisotropic source. We consider the modified Krori-Barua charged isotropic solution for spherical self-gravitating star to deal with the isotropic system. The second set of the field equations is solved by taking two different constraints. We then investigate physical acceptability of the obtained solutions through graphical analysis of the effective physical variables and energy conditions. We also analyze the effects of charge on different parameters, (i.e., mass, compactness and redshift) for the resulting solutions. It is found that our both solutions are viable as well as stable for specific values of the decoupling parameter $φ$ and charge. We conclude that a self-gravitating star shows more stable behavior in this gravity.

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arXiv2024

Viable Wormhole Solutions in Modified Gauss-Bonnet Gravity

In this paper, we use the embedding class-I technique to examine the effect of charge on traversable wormhole geometry in the context of $f(\mathcal{G})$ theory, where $\mathcal{G}$ is the Gauss-Bonnet term. For this purpose, we consider static spherical spacetime with anisotropic matter configuration to investigate the wormhole geometry. The Karmarkar condition is used to develop a shape function for the static wormhole structure. Using this developed shape function, we construct a wormhole geometry that satisfies all the required constraints and connects asymptotically flat regions of the spacetime. To analyze the existence of traversable wormhole geometry, we evaluate the behavior of energy conditions for various models of this theory. This study reveals that viable traversable wormhole solutions exist in this modified theory.

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