arXiv subjects

M. Sharif

Publications and source records attributed to M. Sharif.

At least 253 records · Page 14Linked to original sources

arXiv2012

Effects of Electromagnetic Field on the Dynamical Instability of Cylindrical Collapse

The objective of this paper is to discuss the dynamical instability in the context of Newtonian and post Newtonian regimes. For this purpose, we consider non-viscous heat conducting charged isotropic fluid as a collapsing matter with cylindrical symmetry. Darmois junction conditions are formulated. The perturbation scheme is applied to investigate the influence of dissipation and electromagnetic field on the dynamical instability. We conclude that the adiabatic index $Γ$ has smaller value for such a fluid in cylindrically symmetric than isotropic sphere.

gr-qc↗

arXiv2012

Anisotropic Universe Models in Brans-Dicke Theory

This paper is devoted to study Bianchi type I cosmological model in Brans-Dicke theory with self-interacting potential by using perfect, anisotropic and magnetized anisotropic fluids. We assume that the expansion scalar is proportional to the shear scalar and also take power law ansatz for scalar field. The physical behavior of the resulting models are discussed through different parameters. We conclude that in contrary to the universe model, the anisotropic fluid approaches to isotropy at later times in all cases which is consistent with observational data.

gr-qc↗

arXiv2012

Phantom Energy Accretion by Stringy Charged Black Hole

We investigate the dynamical behavior of phantom energy near stringy magnetically charged black hole. For this purpose, we derive equations of motion for steady-state spherically symmetric flow of phantom energy onto the stringy magnetically charged black hole. It is found that phantom energy accreting onto black hole decreases its mass. Further, the location of critical points of accretion is explored, which yields mass to charge ratio. This ratio implies that accretion process cannot transform a black hole into an extremal black hole or a naked singularity, hence cosmic censorship hypothesis remains valid here.

physics.gen-ph↗

arXiv2012

Black Hole Evaporation in a Noncommutative Charged Vaidya Model

The aim of this paper is to study the black hole evaporation and Hawking radiation for a noncommutative charged Vaidya black hole. For this purpose, we determine spherically symmetric charged Vaidya model and then formulate a noncommutative Reissner-Nordstr$\ddot{o}$m-like solution of this model which leads to an exact $(t-r)$ dependent metric. The behavior of temporal component of this metric and the corresponding Hawking temperature is investigated. The results are shown in the form of graphs. Further, we examine the tunneling process of the charged massive particles through the quantum horizon. It is found that the tunneling amplitude is modified due to noncommutativity. Also, it turns out that black hole evaporates completely in the limits of large time and horizon radius. The effect of charge is to reduce the temperature from maximum value to zero. It is mentioned here that the final stage of black hole evaporation turns out to be a naked singularity.

gr-qc↗

arXiv2011

Isothermal Plasma Wave Properties of the Schwarzschild de-Sitter Black Hole in a Veselago Medium

In this paper, we study wave properties of isothermal plasma for the Schwarzschild de-Sitter black hole in a Veselago medium. We use ADM 3+1 formalism to formulate general relativistic magnetohydrodynamical (GRMHD) equations for the Schwarzschild de-Sitter spacetime in Rindler coordinates. Further, Fourier analysis of the linearly perturbed GRMHD equations for the rotating (non-magnetized and magnetized) background is taken whose determinant leads to a dispersion relation. We investigate wave properties by using graphical representation of the wave vector, the refractive index, change in refractive index, phase and group velocities. Also, the modes of wave dispersion are explored. The results indicate the existence of the Veselago medium.

physics.gen-ph↗

arXiv2011

K-essence Models and Cosmic Acceleration in Generalized Teleparallel Gravity

The generalized teleparallel gravity has been suggested to explain the present cosmic acceleration of the universe. In this paper, we take spatially homogenous and anisotropic Bianchi type $I$ universe in the framework of $F(T)$ gravity. The behavior of accelerating universe is investigated for three purely kinetic k-essence models. We explore equation of state parameter and deceleration parameter for these k-essence models. It is found that all these models exhibit quintessence behavior of the universe.

physics.gen-ph↗

arXiv2011

Anisotropic Dark Energy and the Generalized Second Law of Thermodynamics

We consider a Bianchi type $I$ model in which anisotropic dark energy is interacting with dark matter and anisotropic radiation. With this scenario, we investigate the validity of the generalized second law of thermodynamics. It is concluded that the validity of this law depends on different parameters like shear, skewness and equation of state.

physics.gen-ph↗

arXiv2011

Newtonian and Post Newtonian Expansionfree Fluid Evolution in f(R) Gravity

We consider a collapsing sphere and discuss its evolution under the vanishing expansion scalar in the framework of $f(R)$ gravity. The fluid is assumed to be locally anisotropic which evolves adiabatically. To study the dynamics of the collapsing fluid, Newtonian and post Newtonian regimes are taken into account. The field equations are investigated for a well-known $f(R)$ model of the form $R+δR^2$ admitting Schwarzschild solution. The perturbation scheme is used on the dynamical equations to explore the instability conditions of expansionfree fluid evolution. We conclude that instability conditions depend upon pressure anisotropy, energy density and some constraints arising from this theory.

physics.gen-ph↗

arXiv2011

Interacting Modified Holographic Dark Energy in Kaluza-Klein Universe

The interaction of modified holographic dark energy and dark matter with varying $G$ in flat Kaluza Klein universe is considered. Further, we take infrared cutoff scale $L$ as future event horizon. In this scenario, equations of state parameter as well as evolution are explored. We also check the validity of the generalized second law of thermodynamics. It is interesting to mention here that our results show consistency with the present observations.

physics.gen-ph↗

arXiv2011

Cylinder with Charged Anisotropic Source

We take charged anisotropic fluid cylinder when there is no external pressure acting on the fluid. This is a cylindrical version of the Krori and Barua's method to explore the field equations with anisotropic fluid. We discuss models with positive matter density and pressure that satisfy all the energy and stability conditions. It is found that charge does not vanish at the center of the cylinder. The equilibrium condition as well as physical conditions are discussed. Further, we highlight the connection between our solutions and the charged strange quark stars as well as with dark matter including charged massive particles. The graphical analysis of the matter variables versus charge is given which indicates a physically reasonable matter distribution.

physics.gen-ph↗

arXiv2011

Dispersion Modes of Hot Plasma for Schwarzschild de-Sitter Horizon in a Veselago Medium

We analyze the dispersion modes of hot plasma around Schwarzschild de-Sitter event horizon in the presence of Veselago medium. For this purpose, we apply ADM 3+1 formalism to develop GRMHD equations for the Schwarzschild de-Sitter spacetime. Implementation of linear perturbation yields perturbed GRMHD equations that are used for the Fourier analysis of rotating (non-magnetized and magnetized) plasma. Wave analysis is described by the graphical representation of the wave vector, refractive index, change in refractive index, phase and group velocities. The outcome of this work supports the validity of Veselago medium.

physics.gen-ph↗

arXiv2011

Thermodynamics of a Bardeen black hole in noncommutative space

In this paper, we examine the effects of space noncommutativity on the thermodynamics of a Bardeen charged regular black hole. For a suitable choice of sets of parameters, the behavior of the singularity, horizon, mass function, black hole mass, temperature, entropy and its differential, area and energy distribution of the Bardeen solution have been discussed graphically for both noncommutative and commutative spaces. Graphs show that the commutative coordinates extrapolate all such quantities (except temperature) for a given set of parameters. It is interesting to mention here that these sets of parameters provide the singularity (essential for $r_h>0$) and horizon ($f(r_h)=0$ for $r_h>0$) for the black hole solution in noncommutative space, while for commutative space no such quantity exists.

gr-qc↗

arXiv2011

Quantum Corrections for ABGB Black Hole

In this paper, we study quantum corrections to the temperature and entropy of a regular Ayón-Beato-Garc\'ıa-Bronnikov black hole solution by using tunneling approach beyond semiclassical approximation. We use the first law of black hole thermodynamics as a differential of entropy with two parameters, mass and charge. It is found that the leading order correction to the entropy is of logarithmic form. In the absence of the charge, i.e., $e=0$, these corrections approximate the corresponding corrections for the Schwarzschild black hole.

gr-qc↗

arXiv2011

Energy Content of Colliding Plane Waves using Approximate Noether Symmetries

This paper is devoted to study the energy content of colliding plane waves using approximate Noether symmetries. For this purpose, we use approximate Lie symmetry method of Lagrangian for differential equations. We formulate the first-order perturbed Lagrangian for colliding plane electromagnetic and gravitational waves. It is shown that in both cases, there does not exist

gr-qc↗

arXiv2011

Effects of f(R) Model on the Dynamical Instability of Expansionfree Gravitational Collapse

Dark energy models based on f(R) theory have been extensively studied in literature to realize the late time acceleration. In this paper, we have chosen a viable f(R) model and discussed its effects on the dynamical instability of expansionfree fluid evolution generating a central vacuum cavity. For this purpose, contracted Bianchi identities are obtained for both the usual matter as well as dark source. The term dark source is named to the higher order curvature corrections arising from f(R) gravity. The perturbation scheme is applied and different terms belonging to Newtonian and post Newtonian regimes are identified. It is found that instability range of expansionfree fluid on external boundary as well as on internal vacuum cavity is independent of adiabatic index $Γ$ but depends upon the density profile, pressure anisotropy and f(R) model.

gr-qc↗

arXiv2011

Phantom Accretion onto the Schwarzschild de-Sitter Black Hole

We deal with phantom energy accretion onto the Schwarzschild de-Sitter black hole. The energy flux conservation, relativistic Bernoulli equation and mass flux conservation equation are formulated to discuss the phantom accretion. We discuss the conditions for critical accretion. It is found that mass of the black hole decreases due to phantom accretion. There exist two critical points which lie in the exterior of horizons (black hole and cosmological horizons). The results for the phantom energy accretion onto the Schwarzschild black hole can be recovered by taking $Λ\rightarrow0$.

gr-qc↗

arXiv2011

Dynamics of Non-adiabatic Charged Cylindrical Gravitational Collapse

This paper is devoted to study the dynamics of gravitational collapse in the Misner and Sharp formalism. We take non-viscous heat conducting charged anisotropic fluid as a collapsing matter with cylindrical symmetry. The dynamical equations are derived and coupled with the transport equation for heat flux obtained from the M$\ddot{u}$ller-Israel-Stewart causal thermodynamic theory. We discuss the role of anisotropy, electric charge and radial heat flux over the dynamics of the collapse with the help of coupled equation.

gr-qc↗

arXiv2011

Expansionfree Fluid Evolution and Skripkin Model in f(R) Theory

We consider the modified $f(R)$ theory of gravity whose higher order curvature terms are interpreted as a gravitational fluid or dark source. The gravitational collapse of a spherically symmetric star, made up of locally anisotropic viscous fluid, is studied under the general influence of the curvature fluid. Dynamical equations and junction conditions are modified in the context of f(R) dark energy and by taking into account the expansionfree evolution of the self-gravitating fluid. As a particular example, the Skripkin model is investigated which corresponds to isotropic pressure with constant energy density. The results are compared with corresponding results in General Relativity.

gr-qc↗