arXiv subjects

M. Sharif

Publications and source records attributed to M. Sharif.

At least 217 records · Page 12Linked to original sources

arXiv2013

Structure Scalars In Charged Plane Symmetry

We consider non-adiabatic flow of the fluid possessing dissipation in the form of shearing viscosity in electromagnetic field. The scalar functions (structure scalars) for charged plane symmetry are formulated and are related with the physical variables of the fluid. We also develop a relationship between the Weyl tensor and other physical variables by using Taub mass formalism. The role of electric charge as well as its physical significance for the evolution of the shear tensor and expansion scalar are also explored. Finally, we discuss a special case for dust with cosmological constant.

gr-qc↗

arXiv2013

Reconstruction of Scalar Field Dark Energy Models in Kaluza-Klein Universe

This paper is devoted to study the modified holographic dark energy model by taking its different aspects in the flat Kaluza-Klein universe. We construct the equation of state parameter which evolutes the universe from quintessence region towards the vacuum. It is found that the modified holographic model exhibits instability against small perturbations in the early epoch of the universe but becomes stable in the later times. We also develop its correspondence with some scalar field dark energy models. It is interesting to mention here that all the results are consistent with the present observations.

gr-qc↗

arXiv2013

Analysis of $f(R)$ Theory Corresponding to NADE and NHDE

We develop the connection of $f(R)$ theory with new agegraphic and holographic dark energy models. The function $f(R)$ is reconstructed, regarding the $f(R)$ theory as an effective description for these dark energy models. We show the future evolution of $f$ and conclude that these functions represent distinct pictures of cosmological eras. The cosmological parameters such as equation of state parameter, deceleration parameter, statefinder diagnostic and $ω-ω'$ analysis are investigated which assure the evolutionary paradigm of $f$.

gr-qc↗

arXiv2013

Dynamics of Potentials in Bianchi Type Scalar-Tensor Cosmology

The present study investigates the nature of the field potential via new technique known as reconstruction method for the scalar field potentials. The key point of this technique is the assumption that Hubble parameter is dependent on the scalar field. We consider Bianchi type I universe in the gravitational framework of scalar-tensor gravity and explore the general form of the scalar field potential. In particular, this field potential is investigated for the matter contents like barotropic fluid, the cosmological constant and Chaplygin gas. It is concluded that for a given value of Hubble parameter, one can reconstruct the scalar potentials which can generate the cosmology motivated by these matter contents.

gr-qc↗

arXiv2013

Fermions Tunneling from Charged anti-de Sitter Black Holes

We study Hawking radiation as a phenomenon of tunneling through event horizons of charged torus-like as well as dilaton black holes involving cosmological constant based on Kerner and Mann's formulation. We obtain tunneling probabilities as well as Hawking's emission temperature of outgoing charged particles by applying the semiclassical WKB approximation to the general covariant Dirac equation. The graphical behavior of Hawking temperature and horizon radius is investigated. We find results consistent with those already given in literature.

gr-qc↗

arXiv2013

Spherical Thin-Shell Wormholes and Modified Chaplygin Gas

The purpose of this paper is to construct spherical thin-shell wormhole solutions through cut and paste technique and investigate the stability of these solutions in the vicinity of modified Chaplygin gas. The Darmois-Israel formalism is used to formulate the stresses of the surface concentrating the exotic matter. We explore the stability of the wormhole solutions by using the standard potential method. We conclude that there exist more stable as well as unstable solutions than the previous study with generalized Chaplygin gas \cite{15}.

gr-qc↗

arXiv2013

Fermions Tunneling from Plebanski-Demianski Black Holes

Hawking radiation spectrum via fermions tunneling is investigated through horizon radii of Pleba$\acute{\textmd{n}}$ski-Demia$\acute{\textmd{n}}$ski family of black holes. To this end, we determine the tunneling probabilities for outgoing and incoming charged fermion particles and obtain their corresponding Hawking temperatures. The graphical behavior of Hawking temperatures and horizon radii (cosmological and event horizons) is also studied. We find consistent results with those already available in literature.

gr-qc↗

arXiv2013

Statefinder Diagnostic for Dark Energy Models in Bianchi I Universe

In this paper, we investigate the statefinder, the deceleration and equation of state parameters when universe is composed of generalized holographic dark energy or generalized Ricci dark energy for Bianchi I universe model. These parameters are found for both interacting as well as non-interacting scenarios of generalized holographic or generalized Ricci dark energy with dark matter and generalized Chaplygin gas. We explore these parameters graphically for different situations. It is concluded that these models represent accelerated expansion of the universe.

gr-qc↗

arXiv2013

Cosmology of Holographic and New Agegraphic $f(R,T)$ Models

We consider the $f(R,T)$ theory, where $R$ is the scalar curvature and $T$ is the trace of energy-momentum tensor, as an effective description for the holographic and new agegraphic dark energy and reconstruct the corresponding $f(R,T)$ functions. In this study, we concentrate on two particular models of $f(R,T)$ gravity namely, $R+2A(T)$ and $B(R)+λ{T}$. We conclude that the derived $f(R,T)$ models can represent phantom or quintessence regimes of the universe which are compatible with the current observational data. In addition, the conditions to preserve the generalized second law of thermodynamics are established.

gr-qc↗

arXiv2013

Dynamics of Charged Radiating Collapse in Modified Gauss-Bonnet Gravity

This paper deals with the dynamics of a shearfree charged radiating collapse in modified Gauss-Bonnet gravity. The field equations for shearfree spherical interior geometry of a charged dissipative star are formulated. To study the dynamical behavior of collapsing matter, we derive the dynamical as well as transport equations. We conclude that the gravitational force in modified Gauss-Bonnet gravity is much stronger as compared to general relativity which implies the increase in the rate of collapse. Finally, we study the effect of charge on the dynamics of collapse.

gr-qc↗

arXiv2013

Mechanical Stability of Cylindrical Thin-Shell Wormholes

In this paper, we apply the cut and paste procedure to charged black string for the construction of thin-shell wormhole. We consider the Darmois-Israel formalism to determine the surface stresses of the shell. We take Chaplygin gas to deal with the matter distribution on shell. The radial perturbation approach (preserving the symmetry) is used to investigate the stability of static solutions. We conclude that stable static solutions exist both for uncharged and charged black string thin-shell wormholes for particular values of the parameters.

gr-qc↗

arXiv2013

Study of Center of Mass Energy by Particles Collision in Some Black Holes

This paper is devoted to the study of particles collision for two well-known black holes. We consider particles moving in equatorial plane and calculate their center of mass energy. Firstly, we explore center of mass energy of a regular black hole. In this case, acceleration and collision of particles lead to high center of mass energy which is independent of event horizon and naked singularity. Secondly, we investigate the center of mass energy of Plebanski and Demianski black hole (non-extremal) with zero NUT parameter. Here the center of mass energy depends upon the rotation parameter. We conclude that the center of mass energy becomes infinitely large for both black holes.

physics.gen-ph↗

arXiv2013

Energy Conditions in $f(R,T,R_{μν}T^{μν})$ Gravity

We discuss the validity of the energy conditions in a newly modified theory named as $f(R,T,R_{μν}T^{μν})$ gravity, where $R$ and $T$ represent the scalar curvature and trace of the energy-momentum tensor. The corresponding energy conditions are derived which appear to be more general and can reduce to the familiar forms of these conditions in general relativity, $f(R)$ and $f(R,T)$ theories. The general inequalities are presented in terms of recent values of Hubble, deceleration, jerk and snap parameters. In particular, we use two specific models recently developed in literature to study concrete application of these conditions as well as Dolgov-Kawasaki instability. Finally, we explore $f(R,T)$ gravity as a specific case to this modified theory for exponential and power law models.

gr-qc↗

arXiv2013

Stability of Thin-Shell Wormholes in Nonlinear Electrodynamics

In this paper, we construct thin-shell wormholes by applying the cut and paste procedure to a regular charged black hole in nonlinear electrodynamics field. We discuss different physical aspects of wormholes such as, the possible equation of state to matter shell, attractive or repulsive nature of wormhole and total amount of exotic matter required. The thin-shell equation of motion with and without cosmological constant is also investigated under linearized perturbation. Finally, we explore the stability regions interpreted by the parameter $β$ (speed of sound) and conclude that there are realistic stability regions for some fixed values of parameters.

gr-qc↗

arXiv2013

Shearfree Spherically Symmetric Fluid Models

We try to find some exact analytical models of spherically symmetric spacetime of collapsing fluid under shearfree condition. We consider two types of solutions: one is to impose a condition on the mass function while the other is to restrict the pressure. We obtain totally of five exact models, and some of them satisfy the Darmois conditions.

gr-qc↗

arXiv2013

Effects of Electromagnetic Field on the Dynamical Instability of Expansionfree Gravitational Collapse

In this paper, we discuss the effects of electromagnetic field on the dynamical instability of a spherically symmetric expansionfree gravitational collapse. Darmois junction conditions are formulated by matching interior spherically symmetric spacetime to exterior Reissner-Nordstr$\ddot{o}$m spacetime. We investigate the role of different terms in the dynamical equation at Newtonian and post Newtonian regimes by using perturbation scheme. It is concluded that instability range depends upon pressure anisotropy, radial profile of energy density and electromagnetic field, but not on the adiabatic index $Γ$. In particular, the electromagnetic field reduces the unstable region.

gr-qc↗

arXiv2013

Stability of Anisotropic Cylinder with Zero Expansion

We study the dynamical instability of anisotropic collapsing cylinder with the expansion-free condition, which generates vacuum cavity within fluid distribution. The perturbation scheme is applied to distinguish Newtonian, post-Newtonian and post-post Newtonian terms, which are used for constructing dynamical equation at Newtonian and post-Newtonian regimes. We analyze the role of pressure anisotropy and energy density inhomogeneity on the stability of collapsing cylinder. It turns out that stability of the cylinder depends upon these physical properties of the fluid, not on the stiffness of the fluid.

gr-qc↗

arXiv2013

Stability Analysis of Thin-Shell Wormholes from Charged Black String

In this paper, we construct thin-shell wormholes from charged black string through cut and paste procedure and investigate its stability. We assume modified generalized Chaplygin gas as a dark energy fluid (exotic matter) present in the thin layer of matter-shell. The stability of these constructed thin-shell wormholes is investigated in the scenario of linear perturbations. We conclude that static stable as well as unstable configurations are possible for cylindrical thin-shell wormholes.

gr-qc↗