arXiv subjects

M. Sharif

Publications and source records attributed to M. Sharif.

At least 289 records · Page 16Linked to original sources

arXiv2010

Plasma Wave Properties of the Schwarzschild Magnetosphere in a Veselago Medium

We re-formulate the 3+1 GRMHD equations for the Schwarzschild black hole in a Veselago medium. Linear perturbation in rotating (non-magnetized and magnetized) plasma is introduced and their Fourier analysis is considered. We discuss wave properties with the help of wave vector, refractive index and change in refractive index in the form of graphs. It is concluded that some waves move away from the event horizon in this unusual medium. We conclude that for the rotating non-magnetized plasma, our results confirm the presence of Veselago medium while the rotating magnetized plasma does not provide any evidence for this medium.

gr-qc↗

arXiv2010

Singularity in Gravitational Collapse of Plane Symmetric Charged Vaidya Spacetime

We study the final outcome of gravitational collapse resulting from the plane symmetric charged Vaidya spacetime. Using the field equations, we show that the weak energy condition is always satisfied by collapsing fluid. It is found that the singularity formed is naked. The strength of singularity is also investigated by using Nolan's method. This turns out to be a strong curvature singularity in Tipler's sense and hence provides a counter example to the cosmic censorship hypothesis.

gr-qc↗

arXiv2010

Energy Contents of Some Well-Known Solutions in Teleparallel Gravity

In the context of teleparallel equivalent to General Relativity, we study energy and its relevant quantities for some well-known black hole solutions. For this purpose, we use the Hamiltonian approach which gives reasonable and interesting results. We find that our results of energy exactly coincide with several prescriptions in General Relativity. This supports the claim that different energy-momentum prescriptions can give identical results for a given spacetime. We also evaluate energy-momentum flux of these solutions.

physics.gen-ph↗

arXiv2010

Cold Plasma Wave Analysis in Magneto-Rotational Fluids

This paper is devoted to investigate the cold plasma wave properties. The analysis has been restricted to the neighborhood of the pair production region of the Kerr magnetosphere. The Fourier analyzed general relativistic magnetohydrodynamical equations are dealt under special circumstances and dispersion relations are obtained. We find the $x$-component of the complex wave vector numerically. The corresponding components of the propagation vector, attenuation vector, phase and group velocities are shown in graphs. The direction and dispersion of waves are investigated.

gr-qc↗

arXiv2010

Dynamics of Bianchi I Universe with Magnetized Anisotropic Dark Energy

We study Bianchi type $I$ cosmological model in the presence of magnetized anisotropic dark energy. The energy-momentum tensor consists of anisotropic fluid with anisotropic EoS $p=ωρ$ and a uniform magnetic field of energy density $ρ_B$. We obtain exact solutions to the field equations using the condition that expansion is proportional to the shear scalar. The physical behavior of the model is discussed with and without magnetic field. We conclude that universe model as well as anisotropic fluid do not approach isotropy through the evolution of the universe.

gr-qc↗

arXiv2010

Non-Vacuum Bianchi Types I and V in f(R) Gravity

In a recent paper \cite{1}, we have studied the vacuum solutions of Bianchi types I and V spacetimes in the framework of metric f(R) gravity. Here we extend this work to perfect fluid solutions. For this purpose, we take stiff matter to find energy density and pressure of the universe. In particular, we find two exact solutions in each case which correspond to two models of the universe. The first solution gives a singular model while the second solution provides a non-singular model. The physical behavior of these models has been discussed using some physical quantities. Also, the function of the Ricci scalar is evaluated.

gr-qc↗

arXiv2010

Energy Contents of a Class of Regular Black Hole Solutions in Teleparallel Gravity

In this paper, we discuss the energy-momentum problem in the realm of teleparallel gravity. The energy-momentum distribution for a class of regular black holes coupled with a non-linear electrodynamics source is investigated by using Hamiltonian approach of teleparallel theory. The generalized regular black hole contains two specific parameters $α$ and $β$ (a sort of dipole and quadrupole of non-linear source) on which the energy distribution depends. It is interesting to mention here that our results exactly coincide with different energy-momentum prescriptions in General Relativity.

gr-qc↗

arXiv2010

Kinematic Self-Similar Solutions of Locally Rotationally Symmetric Spacetimes

This paper contains locally rotationally symmetric kinematic self-similar perfect fluid and dust solutions. We consider three families of metrics which admit kinematic self-similar vectors of the first, second, zeroth and infinite kinds, not only for the tilted fluid case but also for the parallel and orthogonal cases. It is found that the orthogonal case gives contradiction both in perfect fluid and dust cases for all the three metrics while the tilted case reduces to the parallel case in both perfect fluid and dust cases for the second metric. The remaining cases give self-similar solutions of different kinds. We obtain a total of seventeen independent solutions out of which two are vacuum. The third metric yields contradiction in all the cases.

gr-qc↗

arXiv2010

Gravitational Charged Perfect Fluid Collapse in Friedmann Universe Models

This paper is devoted to study the gravitational charged perfect fluid collapse in the Friedmann universe models with cosmological constant. For this purpose, we assume that the electromagnetic field is so weak that it does not introduce any distortion into the geometry of the spacetime. The results obtained from the junction conditions between the Friedmann and the Reissner-Nordstr$\ddot{o}$m de-Sitter spacetimes are used to solve the field equations. Further, the singularity structure and mass effects of the collapsing system on time difference between the formation of apparent horizons and singularity have been studied. This analysis provides the validity of Cosmic Censorship Hypothesis. It is found that the electric field affects the area of apparent horizons and their time of formation.

gr-qc↗

arXiv2010

Dynamics of Viscous Dissipative Plane Symmetric Gravitational Collapse

We present dynamical description of gravitational collapse in view of Misner and Sharp's formalism. Matter under consideration is a complicated fluid consistent with plane symmetry which we assume to undergo dissipation in the form of heat flow, radiation, shear and bulk viscosity. Junction conditions are studied for a general spacetime in the interior and Vaidya spacetime in the exterior regions. Dynamical equations are obtained and coupled with causal transport equations derived in context of M$\ddot{u}$ller Israel Stewart theory. The role of dissipative quantities over collapse is investigated.

gr-qc↗

arXiv2010

Effects of the Electromagnetic Field on Five-dimensional Gravitational Collapse

This paper investigates the five-dimensional(5D) spherically symmetric gravitational collapse with positive cosmological constant in the presence of an electromagnetic field. The junction conditions between the 5D non-static interior and the static exterior spacetimes are derived using the Israel criteria modified by Santos. We use the energy conditions to discuss solution to the field equations of the interior spacetime with a charged perfect fluid for the marginally bound and the non-marginally bound cases. We found that the range of apparent horizon was larger than that for 4D gravitational collapse with an electromagnetic field. This analysis gives the irreducible and the reducible extensions of 4D perfect fluid collapse with an electromagnetic field and 5D perfect fluid collapse, respectively. Moreover, for the later case, the results can be recovered under some restrictions.

gr-qc↗

arXiv2009

Energy Distribution in f(R) Gravity

The well-known energy problem is discussed in f(R) theory of gravity. We use the generalized Landau-Lifshitz energy-momentum complex in the framework of metric f(R) gravity to evaluate the energy density of plane symmetric solutions for some general f(R) models. In particular, this quantity is found for some popular choices of f(R) models. The constant scalar curvature condition and the stability condition for these models are also discussed. Further, we investigate the energy distribution of cosmic string spacetime.

gr-qc↗

arXiv2009

Plane Symmetric Solutions in f(R) Gravity

The modified theories of gravity, especially the f(R) theory, have attracted much attention in recent years. In this context, we explore static plane symmetric vacuum solutions using the metric approach of this theory. The field equations are solved using the assumption of constant scalar curvature which may be zero or non-zero. We have found a total of three plane symmetric solutions. The correspondence of these solutions with the well-known solutions in General Relativity is given.

gr-qc↗

arXiv2009

Behavior of Time-varying Constants in Relativity

In this paper, we consider Bianchi type III and Kantowski-Sachs spacetimes and discuss the behavior of time-varying constants $G$ and $Λ$ by using two symmetric techniques, namely, kinematic self-similarity and matter collineation. In the kinematic self-similarity technique, we investigate the behavior of the first and the second kinds. In the matter collineation technique, we consider usual, modified, and completely modified matter collineation equations while studying the behavior of these constants. Further, we reduce the results for dust, radiation, and stiff fluids. We find that $Λ$ is a decreasing time function while $G$ is an increasing time function. This corresponds to the earlier results available in the literature for other spacetimes. Further, we find that the deceleration parameter attains a negative value, which shows that the expansion of the universe is accelerating.

gr-qc↗

arXiv2009

Hot Plasma Waves in Schwarzschild Magnetosphere

In this paper we examine the wave properties of hot plasma living in Schwarzschild magnetosphere. The 3+1 GRMHD perturbation equations are formulated for this scenario. These equations are Fourier analyzed and then solved numerically to obtain the dispersion relations for non-rotating, rotating non-magnetized and rotating magnetized plasma. The wave vector is evaluated which is used to calculate refractive index. These quantities are shown in graphs which are helpful to discuss the dispersive properties of the medium near the event horizon.

gr-qc↗

arXiv2009

Exact Solutions of Bianchi Types $I$ and $V$ Spacetimes in $f(R)$ Theory of Gravity

In this paper, the crucial phenomenon of the expansion of the universe has been discussed. For this purpose, we study the vacuum solutions of Bianchi types $I$ and $V$ spacetimes in the framework of $f(R)$ gravity. In particular, we find two exact solutions in each case by using the variation law of Hubble parameter. These solutions correspond to two models of the universe. The first solution gives a singular model while the second solution provides a non-singular model. The physical behavior of these models is discussed. Moreover, the function of the Ricci scalar is evaluated for both the models in each case.

gr-qc↗

arXiv2009

Energy Contents of Some Non-Vacuum Spacetimes in Teleparallel Gravity

This paper elaborates the problem of energy-momentum in the framework of teleparallel equivalent of General Relativity. For this purpose, we consider energy-momentum prescription derived from the integral form of the constraint equations developed in the Hamiltonian formulation of the teleparallel equivalent of General Relativity. We use this technique to investigate energy-momentum of stationary axisymmetric Einstein-Maxwell solutions and cosmic string spacetimes. The angular momentum, gravitational and matter energy-momentum fluxes of these spacetimes are also evaluated. It is concluded that the results of teleparallel theory are relatively analogous to the results of General Relativity.

gr-qc↗

arXiv2009

Energy Contents of Gravitational Waves in Teleparallel Gravity

The conserved quantities, that are, gravitational energy-momentum and its relevant quantities are investigated for cylindrical and spherical gravitational waves in the framework of teleparallel equivalent of General Relativity using the Hamiltonian approach. For both cylindrical and spherical gravitational waves, we obtain definite energy and constant momentum. The constant momentum shows consistency with the results available in General Relativity and teleparallel gravity. The angular momentum for cylindrical and spherical gravitational waves also turn out to be constant. Further, we evaluate their gravitational energy-momentum fluxes and gravitational pressure.

gr-qc↗