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Cosmic Evolution of Holographic Dark Energy in <math id="M1" xmlns="http://www.w3.org/1998/Math/MathML"><mi>f</mi><mo stretchy="false">(</mo><mi mathvariant="script">G</mi><mo>,</mo><mi>T</mi><mo stretchy="false">)</mo></math> Gravity
https://repo.scoap3.org/record/31971
The aim of this paper is to analyze the cosmological evolution of holographic dark energy in f(G,T) gravity ( G and T represent the Gauss-Bonnet invariant and trace of the energy-momentum tensor, respectively). We reconstruct f(G,T) model through correspondence scheme using power-law form of the scale factor. The qualitative analysis of the derived model is investigated with the help of evolutionary trajectories of equation of state and deceleration as well as state-finder diagnostic parameters and ωGT-ωGT′ cosmological phase plane. It is found that the equation of state parameter represents phantom epoch of the Universe whereas the deceleration parameter illustrates the accelerated phase. The state-finder plane corresponds to Chaplygin gas model while the freezing region is attained in ωGT-ωGT′ plane.Sharif, M.Tue, 09 Apr 2019 15:00:56 GMThttps://repo.scoap3.org/record/31971urn:ISSN:1687-7365Hindawi2019-04-01Models of Collapsing and Expanding Cylindrical Source in <math id="M1" xmlns="http://www.w3.org/1998/Math/MathML"><mi>f</mi><mo stretchy="false">(</mo><mi>R</mi><mo>,</mo><mi>T</mi><mo stretchy="false">)</mo></math> Theory
https://repo.scoap3.org/record/30983
We discuss the collapsing and expanding solutions of anisotropic charged cylinder in the context of f(R,T) theory ( R represents the Ricci scalar and T denotes the trace of energy-momentum tensor). For this purpose, we take an auxiliary solution of Einstein-Maxwell field equations and evaluate expansion scalar whose negative values lead to collapse and positive values give expansion. For both cases, the behavior of density, pressure, anisotropic parameter, and mass is explored and the effects of charge as well as model parameter on these quantities are examined. The energy conditions are found to be satisfied for both solutions.Sharif, M.Thu, 14 Feb 2019 13:16:03 GMThttps://repo.scoap3.org/record/30983urn:ISSN:1687-7365Hindawi2019-02-14Gravitational decoupled anisotropic solutions in f(G) gravity
https://repo.scoap3.org/record/29141
In this paper, we investigate anisotropic static spherically symmetric solutions in the framework of f(G) gravity through gravitational decoupling approach. For this purpose, we consider Krori and Barua (known solution) isotropic interior solution for static spherically symmetric self-gravitating system and extend it to two types of anisotropic solutions. We examine the physical viability of our models through energy conditions, squared speed of sound and anisotropy parameter. It is found that the first solution is physically viable as it fulfills the energy bounds as well as stability criteria while the second solution satisfies all energy bounds but is unstable at the core of the compact star.Sharif, M.Tue, 13 Nov 2018 04:20:37 GMThttps://repo.scoap3.org/record/29141urn:ISSN:1434-6052Springer/Società Italiana di Fisica2018-11-13Anisotropic quark stars in f ( R , T ) gravity
https://repo.scoap3.org/record/28812
The aim of this paper is to analyze the nature of anisotropic spherically symmetric relativistic star models in the framework of f ( R , T ) gravity. To discuss the features of compact stars, we consider that in the interior of the stellar system, the fluid distribution is influenced by MIT bag model equation of state. We construct the field equations by employing Krori–Barua solutions and obtain the values of unknown constants with the help of observational data of Her X-1, SAX J 1808.4-3658, RXJ 1856-37 and 4U1820-30 star models. For a viable f ( R , T ) model, we study the behavior of energy density, transverse as well as radial pressure and anisotropic factor in the interior of these stars for a specific value of the bag constant. We check the physical viability of our proposed model and stability of stellar structure through energy conditions, causality condition and adiabatic index. It is concluded that our model satisfies the stability criteria as well as other physical requirements, and the value of bag constant is in well agreement with the experimental value which highlights the viability of our considered model.Sharif, M.Sat, 27 Oct 2018 19:08:23 GMThttps://repo.scoap3.org/record/28812urn:ISSN:1434-6052Springer/Società Italiana di Fisica2018-10-27Complexity factor for static cylindrical system
https://repo.scoap3.org/record/28714
In this paper, we investigate the complexity factor for static cylindrical configuration with anisotropic fluid distribution. We establish field equations, Tolman–Opphenheimer–Volkoff equation, and mass function. We also evaluate structure scalars using orthogonal splitting of the Riemann tensor which leads to the complexity factor. Finally, we deduce some results about stellar objects for vanishing complexity condition.Sharif, M.Tue, 23 Oct 2018 03:24:15 GMThttps://repo.scoap3.org/record/28714urn:ISSN:1434-6052Springer/Società Italiana di Fisica2018-10-22Thermodynamics of Modified Cosmic Chaplygin Gas
https://repo.scoap3.org/record/28373
We examine the thermodynamic features of an exotic fluid known as modified cosmic Chaplygin gas in the context of homogeneous isotropic universe model. For this purpose, the behavior of physical parameters is discussed that help to analyze nature of the universe. Using specific heat formalism, the validity of third law of thermodynamics is checked. Furthermore, with the help of thermodynamic entities, the thermal equation of state is also discussed. The thermodynamic stability is explored by means of adiabatic, specific heat and isothermal conditions from classical thermodynamics. It is concluded that the considered fluid configuration is thermodynamically stable and expands adiabatically for an appropriate choice of parameters.Sharif, M.Wed, 03 Oct 2018 20:16:06 GMThttps://repo.scoap3.org/record/28373urn:ISSN:1687-7365Hindawi2018-10-03Curvature-matter coupling effects on axial gravitational waves
https://repo.scoap3.org/record/27853
In this paper, we investigate propagation of axial gravitational waves in the background of flat FRW universe in f ( R , T ) theory. The field equations are obtained for unperturbed as well as axially perturbed FRW metric. These field equations are solved simultaneously to obtain the unknown perturbation parameters. We find that the assumed perturbations can affect matter as well as four velocity. Moreover, ignoring the material perturbations we explicitly obtain an expression for four velocity. It is concluded that axial gravitational waves in the curvature-matter coupling background can produce cosmological rotation or have memory effect if the wave profile has discontinuity at the wave front.Sharif, M.Thu, 06 Sep 2018 04:46:46 GMThttps://repo.scoap3.org/record/27853urn:ISSN:1434-6052Springer/Società Italiana di Fisica2018-9-6Complexity factor for charged spherical system
https://repo.scoap3.org/record/27677
In this paper, we study the complexity factor for a charged anisotropic self-gravitating object. We formulate the Einstein–Maxwell field equations, Tolman–Opphenheimer–Volkoff equation, and the mass function. We form the structure scalars by the orthogonal splitting of the Riemann tensor and then find the complexity factor with the help of these scalars. Finally, we investigate some astrophysical objects for the vanishing of complexity condition. It is found that the presence of the electromagnetic field decreases the complexity of the system.Sharif, M.Wed, 29 Aug 2018 17:07:48 GMThttps://repo.scoap3.org/record/27677urn:ISSN:1434-6052Springer/Società Italiana di Fisica2018-8-29Gravitational decoupled charged anisotropic spherical solutions
https://repo.scoap3.org/record/25743
The purpose of this paper is to obtain exact solutions for charged anisotropic spherically symmetric matter configuration. For this purpose, we consider known solution for isotropic spherical system in the presence of electromagnetic field and extend it to two types of anisotropic charged solutions through gravitational decoupling approach. We examine physical characteristics of the resulting models. It is found that only first solution is physically acceptable as it meets all the energy bounds as well as stability criterion. We conclude that stability of the first model is enhanced with the increase of charge.Sharif, M.Thu, 24 May 2018 14:57:43 GMThttps://repo.scoap3.org/record/25743urn:ISSN:1434-6052Springer/Società Italiana di Fisica2018-5-24Thermodynamics in <math id="M1" xmlns="http://www.w3.org/1998/Math/MathML"><mi>f</mi><mo stretchy="false">(</mo><mi mathvariant="script">G</mi><mo>,</mo><mi>T</mi><mo stretchy="false">)</mo></math> Gravity
https://repo.scoap3.org/record/24212
This paper explores the nonequilibrium behavior of thermodynamics at the apparent horizon of isotropic and homogeneous universe model in f(G,T) gravity ( G and T represent the Gauss-Bonnet invariant and trace of the energy-momentum tensor, resp.). We construct the corresponding field equations and analyze the first as well as generalized second law of thermodynamics in this scenario. It is found that an auxiliary term corresponding to entropy production appears due to the nonequilibrium picture of thermodynamics in first law. The universal condition for the validity of generalized second law of thermodynamics is also obtained. Finally, we check the validity of generalized second law of thermodynamics for the reconstructed f(G,T) models (de Sitter and power-law solutions). We conclude that this law holds for suitable choices of free parameters.Sharif, M.Thu, 08 Mar 2018 17:16:10 GMThttps://repo.scoap3.org/record/24212urn:ISSN:1687-7365Hindawi2018-03-08Lorentz Distributed Noncommutative <math id="M1" xmlns="http://www.w3.org/1998/Math/MathML"><mi>F</mi><mo stretchy="false">(</mo><mi>T</mi><mo>,</mo><msub><mrow><mi>T</mi></mrow><mrow><mi>G</mi></mrow></msub><mo stretchy="false">)</mo></math> Wormhole Solutions
https://repo.scoap3.org/record/23590
The aim of this paper is to study static spherically symmetric noncommutative F(T,TG) wormhole solutions along with Lorentzian distribution. Here, T and TG are torsion scalar and teleparallel equivalent Gauss-Bonnet term, respectively. We take a particular redshift function and two F(T,TG) models. We analyze the behavior of shape function and also examine null as well as weak energy conditions graphically. It is concluded that there exist realistic wormhole solutions for both models. We also studied the stability of these wormhole solutions through equilibrium condition and found them stable.Sharif, M.Wed, 07 Feb 2018 17:16:09 GMThttps://repo.scoap3.org/record/23590urn:ISSN:1687-7365Hindawi2018-02-07Cosmological analysis of reconstructed F(T,TG) models
https://repo.scoap3.org/record/23589
In this paper, we analyze cosmological consequences of the reconstructed generalized ghost pilgrim dark energy F(T,TG) models in terms of redshift parameter z . For this purpose, we consider power-law scale factor, scale factor for two unified phases and intermediate scale factor. We discuss graphical behavior of the reconstructed models and examine their stability analysis. Also, we explore the behavior of equation of state as well as deceleration parameters and ωΛ-ωΛ′ as well as r-s planes. It is found that all models are stable for pilgrim dark energy parameter 2. The equation of state parameter satisfies the necessary condition for pilgrim dark energy phenomenon for all scale factors. All other cosmological parameters show great consistency with the current behavior of the universe.Sharif, M.Wed, 07 Feb 2018 13:40:32 GMThttps://repo.scoap3.org/record/23589urn:ISSN:1434-6052Springer/Società Italiana di Fisica2018-1-27Influence of f(R) models on the existence of anisotropic self-gravitating systems
https://repo.scoap3.org/record/21981
This paper aims to explore some realistic configurations of anisotropic spherical structures in the background of metric f ( R ) gravity, where R is the Ricci scalar. The solutions obtained by Krori and Barua are used to examine the nature of particular compact stars with three different modified gravity models. The behavior of material variables is analyzed through plots and the physical viability of compact stars is investigated through energy conditions. We also discuss the behavior of different forces, equation of state parameter, measure of anisotropy and Tolman–Oppenheimer–Volkoff equation in the modeling of stellar structures. The comparison from our graphical representations may provide evidence for the realistic and viable f ( R ) gravity models at both theoretical and the astrophysical scale.Yousaf, Z.Fri, 20 Oct 2017 16:37:52 GMThttps://repo.scoap3.org/record/21981urn:ISSN:1434-6052Springer/Società Italiana di Fisica2017-10-20Particle dynamics near Kerr-MOG black hole
https://repo.scoap3.org/record/20317
This paper explores the dynamics of both neutral and charged particles orbiting near a rotating black hole in scalar–tensor–vector gravity. We study the conditions for the particle to escape at the innermost stable circular orbit. We investigate the stability of orbits through the effective potential and Lyapunov exponent in the presence of a magnetic field. The effective force acting on particle is also discussed. We also study the center of mass energy of particle collision near the horizon of this black hole. Finally, we compare our results with the particle motion around Schwarzschild, Kerr and Schwarzschild-MOG black holes. It is concluded that the external magnetic field, spin parameter and dimensionless parameter of the theory have strong effects on the particle dynamics in modified gravity.Sharif, M.Wed, 31 May 2017 21:34:24 GMThttps://repo.scoap3.org/record/20317urn:ISSN:1434-6052Springer/Società Italiana di Fisica2017-5-31Cosmological analysis of scalar field models in f ( R , T ) gravity
https://repo.scoap3.org/record/19513
This paper determines the existence of Noether symmetry in non-minimally coupled f ( R , T ) gravity admitting minimal coupling with scalar field models. We consider a generalized spacetime which corresponds to different anisotropic and homogeneous universe models. We formulate symmetry generators along with conserved quantities through Noether symmetry technique for direct and indirect curvature–matter coupling. For dust and perfect fluids, we evaluate exact solutions and construct their cosmological analysis through some cosmological parameters. We conclude that decelerated expansion is obtained for the quintessence model with a dust distribution, while a perfect fluid with dominating potential energy over kinetic energy leads to the current cosmic expansion for both phantom as well as quintessence models.Sharif, M.Tue, 28 Mar 2017 16:49:08 GMThttps://repo.scoap3.org/record/19513urn:ISSN:1434-6052Springer/Società Italiana di Fisica2017-3-28Stability of the accelerated expansion in nonlinear electrodynamics
https://repo.scoap3.org/record/19168
This paper is devoted to the phase space analysis of an isotropic and homogeneous model of the universe by taking a noninteracting mixture of the 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 the stability of the system, we find corresponding critical points for different values of the parameters. We also evaluate the power-law scale factor whose behavior indicates different phases of the universe in this model. It is concluded that the bulk viscosity as well as electromagnetic field enhances the stability of the accelerated expansion of the isotropic and homogeneous model of the universe.Sharif, M.Mon, 27 Feb 2017 21:36:29 GMThttps://repo.scoap3.org/record/19168urn:ISSN:1434-6052Springer/Società Italiana di Fisica2017-2-27Energy conditions in f(G,T) gravity
https://repo.scoap3.org/record/18000
The aim of this paper is to introduce a new modified gravity theory named f(G,T) gravity ( 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 an extra force. We express the energy conditions in terms of cosmological parameters like the deceleration, jerk, and snap parameters. The reconstruction technique is applied to this theory using de Sitter and power-law cosmological solutions. We analyze the energy bounds and obtain feasible constraints on the free parameters.Sharif, M.Wed, 23 Nov 2016 08:30:28 GMThttps://repo.scoap3.org/record/18000urn:ISSN:1434-6052Springer/Società Italiana di Fisica2016-11-22Shadow of a charged rotating non-commutative black hole
https://repo.scoap3.org/record/17960
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 a 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 a 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.Sharif, M.Fri, 18 Nov 2016 14:09:34 GMThttps://repo.scoap3.org/record/17960urn:ISSN:1434-6052Springer/Società Italiana di Fisica2016-11-18Electromagnetic effects on cracking of anisotropic polytropes
https://repo.scoap3.org/record/17597
In this paper, we study the electromagnetic effects on the stability of a 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 the polytropic constant as well as the polytropic index and formulate the force distribution function. It is found that the compact object is stable for a feasible choice of perturbed polytropic index in the presence of charge.Sharif, MuhammadFri, 21 Oct 2016 18:12:19 GMThttps://repo.scoap3.org/record/17597urn:ISSN:1434-6052Springer/Società Italiana di Fisica2016-10-21Stability of the Regular Hayward Thin-Shell Wormholes
https://repo.scoap3.org/record/16630
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 ar>0 and ar<0 , respectively. We also explore stability conditions for the existence of traversable thin-shell wormholes with arbitrarily small amount of fluid describing cosmic expansion. We find that the space-time has nonphysical regions which give rise to event horizon for 0<a0<2.8 and the wormhole becomes nontraversable producing a black hole. The nonphysical 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.Sharif, M.Sun, 31 Jul 2016 12:16:07 GMThttps://repo.scoap3.org/record/16630urn:ISSN:1687-7365Hindawi Publishing Corporation2016-07-31Dynamics of particles near black hole with higher dimensions
https://repo.scoap3.org/record/16463
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 a Myers–Perry black hole with arbitrary extra dimensions as well as a single non-zero spin parameter. Assuming it as a supermassive black hole at the center of the galaxy, we calculate red–blue shifts in the equatorial plane for the far away observer as well as the corresponding black hole parameters of the photons. Next, we study the Penrose process and find that the energy gain of the particle depends on the variation of the black hole dimensions. Finally, we discuss the center of mass energy for 11 dimensions, which indicates a similar behavior to 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.Sharif, M.Sat, 16 Jul 2016 11:52:54 GMThttps://repo.scoap3.org/record/16463urn:ISSN:1434-6052Springer/Società Italiana di Fisica2016-7-16Dynamics of axial symmetric system in self-interacting Brans–Dicke gravity
https://repo.scoap3.org/record/16054
This paper investigates the dynamics of an axial reflection symmetric model in self-interacting Brans–Dicke gravity for anisotropic fluid. We formulate hydrodynamical equations and discuss oscillations using a time-dependent perturbation for both spin-dependent and spin-independent cases. The expressions of the frequency, the total energy density, and the equation of motion of the oscillating model are obtained. We study the instability of the 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 .Sharif, M.Thu, 16 Jun 2016 12:39:42 GMThttps://repo.scoap3.org/record/16054urn:ISSN:1434-6052Springer/Società Italiana di Fisica2016-6-16Stellar filaments in self-interacting Brans–Dicke gravity
https://repo.scoap3.org/record/15679
This paper is devoted to the study of the cylindrically symmetric stellar filaments in self-interacting Brans–Dicke gravity. For this purpose, we construct polytropic filamentary models through a generalized Lane–Emden equation in the Newtonian regime. The resulting models depend upon the values of the cosmological constant (due to the scalar field) along with the polytropic index and represent a generalization of the corresponding models in general relativity. We also investigate the fragmentation of the filaments by exploring the radial oscillations through a stability analysis. This stability criterion depends only upon the adiabatic index.Sharif, M.Wed, 18 May 2016 16:58:56 GMThttps://repo.scoap3.org/record/15679urn:ISSN:1434-6052Springer/Società Italiana di Fisica2016-5-18Accretion onto a charged higher-dimensional black hole
https://repo.scoap3.org/record/14782
This paper deals with the steady-state polytropic fluid accretion onto a higher-dimensional Reissner–Nordström 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 the critical radius, the critical sound velocity, and the critical flow velocity. We also explore gas compression and temperature profiles to analyze the asymptotic behavior. It is found that the results for the Schwarzschild black hole are recovered when q=0 in four dimensions. We conclude that the accretion process in higher dimensions becomes slower in the presence of charge.Sharif, M.Wed, 16 Mar 2016 14:48:43 GMThttps://repo.scoap3.org/record/14782urn:ISSN:1434-6052Springer/Società Italiana di Fisica2016-3-16Corrigendum to “Null Geodesics and Strong Field Gravitational Lensing in a String Cloud Background”
https://repo.scoap3.org/record/13527
Sharif, M.Thu, 21 Jan 2016 14:36:00 GMThttps://repo.scoap3.org/record/13527urn:ISSN:1687-7365Hindawi Publishing Corporation2015-08-18