arXiv subjects

M. Sharif

Publications and source records attributed to M. Sharif.

At least 181 records · Page 10Linked to original sources

arXiv2017

Axial Dissipative Dust as a Source of Gravitational Radiation in f(R) Gravity

In this paper, we explore the source of gravitational radiation in the context of $f(R)$ gravity by considering axially symmetric dissipative dust under geodesic condition. We evaluate scalars associated with electric and magnetic parts of the Weyl tensor for both non-spinning (at the center) and spinning (in the surrounding of the center) fluids of the configuration. For this purpose, we use the evolution as well as constraint equations for kinematical quantities and Weyl tensor. Finally, we investigate the existence of gravitational radiation through super-Poynting vector. It is found that the fluid is not gravitationally radiating in the non-spinning case but it is gravitationally radiating for the spinning case.

gr-qc↗

arXiv2017

Stability of Accelerated Expansion in Nonlinear Electrodynamics

This paper is devoted to study the phase space analysis of isotropic and homogenous universe model by taking a noninteracting mixture of electromagnetic and viscous radiating fluids whose viscous pressure satisfies a nonlinear version of the Israel-Stewart transport equation. We establish an autonomous system of equations by introducing normalized dimensionless variables. In order to analyze stability of the system, we find corresponding critical points for different values of the parameters. We also evaluate power-law scale factor whose behavior indicates different phases of the universe model. It is concluded that bulk viscosity as well as electromagnetic field enhances the stability of accelerated expansion of the isotropic and homogeneous universe model.

gr-qc↗

arXiv2016

Energy Conditions in $f(\mathcal{G},T)$ Gravity

The aim of this paper is to introduce a new modified gravity theory named as $f(\mathcal{G},T)$ gravity ($\mathcal{G}$ and $T$ are the Gauss-Bonnet invariant and trace of the energy-momentum tensor, respectively) and investigate energy conditions for two reconstructed models in the context of FRW universe. We formulate general field equations, divergence of energy-momentum tensor, equation of motion for test particles as well as corresponding energy conditions. The massive test particles follow non-geodesic lines of geometry due to the presence of extra force. We express energy conditions in terms of cosmological parameters like deceleration, jerk and snap parameters. The reconstruction technique is applied to this theory using de Sitter and power-law cosmological solutions. We analyze energy bounds and obtain feasible constraints on free parameters.

gr-qc↗

arXiv2016

Shadow of a Charged Rotating Non-Commutative Black Hole

This paper investigates the shadow of a charged rotating non-commutative black hole. For this purpose, we first formulate the null geodesics and study the effects of non-commutative charge on the photon orbit. We then explore the effect of spin, angle of inclination as well as non-commutative charge on the silhouette of the shadow. It is found that shape of the shadow deviates from the circle with the decrease in the non-commutative charge. We also discuss observable quantities to study the deformation and distortion in the shadow cast by the black hole which decreases for small values of non-commutative charge. Finally, we study the shadows in the presence of plasma. We conclude that the non-commutativity has a great impact on the black hole shadow.

gr-qc↗

arXiv2016

Electromagnetic Effects on Cracking of Anisotropic Polytropes

In this paper, we study the electromagnetic effects on stability of spherically symmetric anisotropic fluid distribution satisfying two polytropic equations of state and construct the corresponding generalized Tolman Oppenheimer Volkoff equations. We apply perturbations on matter variables via polytropic constant as well as polytropic index and formulate the force distribution function. It is found that the compact object is stable for feasible choice of perturbed polytropic index in the presence of charge.

gr-qc↗

arXiv2016

Warm Inflation in $f(\mathcal{G})$ Theory of Gravity

The aim of this paper is to explore warm inflation in the background of $f(\mathcal{G})$ theory of gravity using scalar fields for the FRW universe model. We construct the field equations under slow-roll approximations and evaluate the slow-roll parameters, scalar and tensor power spectra and their corresponding spectral indices using viable power-law model. These parameters are evaluated for a constant as well as variable dissipation factor during intermediate and logamediate inflationary epochs. We also find the number of e-folds and tensor-scalar ratio for each case. The graphical behavior of these parameters proves that the isotropic model in $f(\mathcal{G})$ gravity is compatible with observational Planck data.

gr-qc↗

arXiv2016

Stability of the Regular Hayward Thin-Shell Wormholes

The aim of this paper is to construct regular Hayward thin-shell wormholes and analyze their stability. We adopt Israel formalism to calculate surface stresses of the shell and check the null and weak energy conditions for the constructed wormholes. It is found that the stress-energy tensor components violate the null and weak energy conditions leading to the presence of exotic matter at the throat. We analyze the attractive and repulsive characteristics of wormholes corresponding to $a^r>0$ and $a^r<0$, respectively. We also explore stability conditions for the existence of traversable thin-shell wormholes with arbitrarily small amount of fluids describing cosmic expansion. We find that the spacetime has non-physical regions which give rise to event horizon for $0<a_{0}<2.8$ and the wormhole becomes non-traversable producing a black hole. The non-physical region in the wormhole configuration decreases gradually and vanishes for the Hayward parameter $l=0.9$. It is concluded that the Hayward and Van der Waals quintessence parameters increase the stability of thin-shell wormholes.

gr-qc↗

arXiv2016

Dynamics of Particles Near Black Hole with Higher Dimensions

This paper explores the dynamics of particles in higher dimensions. For this purpose, we discuss some interesting features related to the motion of particles near Myers-Perry black hole with arbitrary extra dimensions as well as single non-zero spin parameter. Assuming it as a supermassive black hole at the center of galaxy, we calculate red-blue shifts in the equatorial plane for the far away observer as well as corresponding black hole parameters of the photons. Next, we study the Penrose process and find that the energy gain of particle depends on the variation of black hole dimensions. Finally, we discuss the center of mass energy for eleven dimensions which indicates similar behavior as that of four dimensions but it is higher in four dimensions than five or more dimensions. We conclude that higher dimensions have a great impact on the particle dynamics.

gr-qc↗

arXiv2016

Dynamical Instability of Gaseous Sphere in the Reissner-Nordstrom Limit

In this paper, we study the dynamical instability of gaseous sphere under radial oscillations approaching the Reissner-Nordström limit. For this purpose, we derive linearized perturbed equation of motion following the Eulerian and Lagrangian approaches. We formulate perturbed pressure in terms of adiabatic index by employing the conservation of baryon numbers. A variational principle is established to evaluate characteristic frequencies of oscillations which lead to the criteria for dynamical stability. The dynamical instability of homogeneous sphere as well as relativistic polytropes with different values of charge in Newtonian and post-Newtonian regimes is explored. We also find their radii of instability in terms of the Reissner-Nordstrom radius. We conclude that dynamical instability occurs if the gaseous sphere contracts to the Reissner-Nordstörm radius for different values of charge.

gr-qc↗

arXiv2016

Instability Analysis of Cylindrical Stellar Object in Brans-Dicke Gravity

This paper investigates instability ranges of a cylindrically symmetric collapsing stellar object in Brans-Dicke theory of gravity. For this purpose, we use perturbation approach in the modified field equations as well as dynamical equations and construct a collapse equation. The collapse equation with adiabatic index ($Γ$) is used to explore the instability ranges of both isotropic as well as anisotropic fluid in Newtonian and post-Newtonian approximations. It turns out that the instability ranges depend on the dynamical variables of collapsing fluid. We conclude that the system always remains unstable for $0<Γ<1$ while $Γ>1$ provides instability only for the special case.

gr-qc↗

arXiv2016

Dynamics of Axial Symmetric System in Self-Interacting Brans-Dicke Gravity

This paper investigates dynamics of axial reflection symmetric model in self-interacting Brans-Dicke gravity for anisotropic fluid. We formulate hydrodynamical equations and discuss oscillations using time-dependent perturbation for both spin as well as spin-independent cases. The expressions of frequency, total energy density and equation of motion of oscillating model are obtained. We study instability of oscillating models in weak approximations. It is found that the oscillations and stability of the model depend upon the dark energy source along with anisotropy and reflection effects. We conclude that the axial reflection system remains stable for stiffness parameter $Γ=1$, collapses for $Γ>1$ and becomes unstable for $0<Γ<1$.

gr-qc↗

arXiv2016

Stellar Filaments in Self-Interacting Brans-Dicke Gravity

This paper is devoted to study cylindrically symmetric stellar filaments in self-interacting Brans-Dicke gravity. For this purpose, we construct polytropic filamentary models through generalized Lane-Emden equation in Newtonian regime. The resulting models depend upon the values of cosmological constant (due to scalar field) along with polytropic index and represent a generalization of the corresponding models in general relativity. We also investigate fragmentation of filaments by exploring the radial oscillations through stability analysis. This stability criteria depends only upon the adiabatic index.

physics.gen-ph↗

arXiv2016

Accretion Onto a Charged Higher-Dimensional Black Hole

This paper deals with the steady-state polytropic fluid accretion onto a higher-dimensional Reissner-Nordstr$\ddot{o}$m black hole. We formulate the generalized mass flux conservation equation, energy flux conservation and relativistic Bernoulli equation to discuss the accretion process. The critical accretion is investigated by finding critical radius, critical sound velocity and critical flow velocity. We also explore gas compression and temperature profiles to analyze the asymptotic behavior. It is found that the results for Schwarzschild black hole are recovered when $q=0$ in four dimensions. We conclude that accretion process in higher dimensions becomes slower in the presence of charge.

gr-qc↗

arXiv2015

Stability Analysis of Axial Reflection Symmetric Spacetime

In this paper, we explore instability regions of non-static axial reflection symmetric spacetime with anisotropic source in the interior. We impose linear perturbation on the Einstein field equations and dynamical equations to establish the collapse equation. The effects of different physical factors like energy density and anisotropic stresses on the instability regions are studied under Newtonian and post-Newtonian limits. We conclude that stiffness parameter has a significant role in this analysis while the reflection terms increase instability ranges of non-static axial collapse.

physics.gen-ph↗

arXiv2015

Dynamics of Scalar Thin-Shell for a Class of Regular Black Holes

This paper is devoted to study the dynamical behavior of thin-shell composed of perfect fluid by considering matter field as a scalar field. We formulate equation of motion of the shell by using Israel thin-shell formalism for a class of regular black holes as interior and exterior regions. The corresponding scalar fields and effective potentials are investigated numerically for both massless and massive scalar fields. We conclude that massless scalar shell leads to collapse, expansion and equilibrium while the massive case leads to collapse only.

physics.gen-ph↗

arXiv2015

Hydrodynamics of Gaseous System in Massive Brans-Dicke Gravity

This paper explores hydrodynamics and hydrostatic of a star in post-Newtonian approximation of massive Bran-Dicke gravity. We study approximated solution of the field equations upto $O(c^{-4})$ and generalize Euler equation of motion. We then formulate equations governing hydrodynamics, stability and instability of the system. Finally, we discuss spherically symmetric stars for a specific barptropic case like dust, cosmic string and domain wall in this scenario.

gr-qc↗

arXiv2015

Inflationary Weak Anisotropic Model with General Dissipation Coefficient

This paper explores the dynamics of warm intermediate and logamediate inflationary models during weak dissipative regime with a general form of dissipative coefficient. We analyze these models within the framework of locally rotationally symmetric Bianchi type I universe. In both cases, we evaluate solution of inflaton, effective scalar potential, dissipative coefficient, slow-roll parameters, scalar and tensor power spectra, scalar spectral index and tensor to scalar ratio under slow-roll approximation. We constrain the model parameters using recent data and conclude that anisotropic inflationary universe model with generalized dissipation coefficient remains compatible with WMAP9, Planck and BICEP2 data.

gr-qc↗

arXiv2015

Instability of Meridional Axial System in f(R) Gravity

We analyze dynamical instability of non-static reflection axial stellar structure by taking into account generalized Euler's equation in metric $f(R)$ gravity. Such an equation is obtained by contracting Bianchi identities of usual anisotropic and effective stress-energy tensors, which after using radial perturbation technique gives modified collapse equation. In the realm of $R+εR^n$ gravity model, we investigate instability constraints at Newtonian and post-Newtonian approximations. We find that instability of meridional axial self-gravitating system depends upon static profile of structure coefficients while $f(R)$ extra curvature terms induce stability to the evolving celestial body.

gr-qc↗