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Tidal Forces in Dyonic Reissner-Nrdstrom Black Hole

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Communications in Theoretical Physics 2018年第3期69卷 257-262页

作者： m.sharif Lubna Kousar Department of mathematics University of the Punjab Quaid-e-Azam Campus Lahore-54590 Pakistan

This paper investigates the tidal as well as magnetic charge effects produced in dyonic Reissner-Nordstroom black *** evaluate Newtonian radial acceleration using radial geodesics for freely falling test *** establish system of equations governing radial and angular tidal forces using geodesic deviation equation and discuss their solutions for bodies falling freely towards this black *** radial tidal force turns out to be compressing outside the event horizon whereas the angular tidal force changes sign between event and Cauchy horizons unlike Schwarzschild black *** radial geodesic component starts decreasing in dyonic Reissner-Nordstroom black hole unlike Schwarzschild *** conclude that magnetic charge strongly affects the radial as well as angular components of tidal force.

关键词： dyonic black hole tidal forces geodesics

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

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Communications in Theoretical Physics 2013年第8期60卷 183-188页

作者： m.sharif Abdul Jawad Department of mathematics University of the PunjabQuaid-e-Azam CampusLahore-54590Pakistan

This paper is devoted to study the modified holographic dark energy model by taking its different aspects in the t/at Kaiuza-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 ail the results are consistent with the present observations.

关键词： Kaluza-Klein cosmology modified holographic dark energy scalar field models

Evolution of Dissipative Anisotropic Expansion-Free Axial Fluids

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Communications in Theoretical Physics 2015年第8期64卷 139-144页

作者： m.sharif Zunaira Nasir Department of mathematics University of the Punjab Quaid-i-Azam Campus

A general study of non-static restricted class of axial system with anisotropic dissipative expansion-free fluid under geodesic condition is carried out. It is found that expansion-free model must be dissipative under geodesic condition to preserve axial symmetry. We also investigate this system without geodesic condition. Finally, the role of dissipation is explored via transport equation.

关键词： general relativity dissipative systems analytical

Viscosity Effects on Anisotropic Universe in Curvature-matter Coupling Gravity

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Communications in Theoretical Physics 2018年第5期69卷 537-543页

作者： m.sharif Aisha Siddiqa Department of mathematics University of the PunjabQuaid-e-Azam Campus

In this paper, we study evolution of the universe in the background of f(R, T) gravity using LRS Bianchi type-Ⅰ model. We discuss scale factors as well as deceleration parameter in dark energy dominated era for different bulk viscosity models. The occurrence of big-rip singularity is also examined. It is concluded that expansion is faster when bulk viscosity is proportional to Hubble parameter as compared to other models.

关键词： f(R T) gravity anisotropic universe bulk viscosity

Teleparallel Killing Vectors of Spherically Symmetric Spacetimes

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Communications in Theoretical Physics 2009年第9期52卷 435-440页

作者： m.sharif Bushra majeed Department of mathematics University of the Punjab

In this paper, Killing vectors of spherically spacetimes have been evaluated in the context of teleparallel theory of gravitation. Further, we investigate the Killing vectors of the Friedmann metrics. It is found that for static spherically spacetimes the number of Killing vectors turns out to be seven while for the Friedmann models, we obtain six teleparallel Killing vectors. The results are then compared with those of General Relativity. We conclude that both of these descriptions of gravity do not provide the consistent results in general. However, these results may coincide under certain conditions for a particular spacetime.

关键词： teleparallel theory Killing vectors

Effects of f(R) model on Dynamics of Axial Shear-Free Dissipative Fluids

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Communications in Theoretical Physics 2016年第4期65卷 483-491页

作者： m.sharif Zunaira Nasir Department of mathematics University of the Punjab

We present a general analysis on non-static axial system with dissipative shear-free anisotropic fluid using polynomial inflationary f(R) *** study the effects of dissipation on the dynamics of geodesic matter *** leads the system either to rotation-free or expansion-free but not both simultaneously under geodesic *** is found that the system preserves its symmetry in both *** the rotation-free case,when there is no dissipation and Ricci scalar is constant,the axial system reduces to FRW universe *** is exactly the same result obtained in general relativity.

关键词： f(R) gravity dissipative systems self-gravitating systems

Phase Space Analysis and Anisotropic Universe model in f(T) Gravity

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Communications in Theoretical Physics 2015年第2期63卷 168-180页

作者： m.sharif Saima Jabbar Department of mathematics University of the Punjab Quaid-e-Azam Campus

In this paper, we study the stability of locally rotationally symmetric （LRS） Bianchi I universe model in f（T） gravity through phase space analysis. We assume that the f（T） gravity can be treated as effective dark energy behaving like perfect fluid, and suggest that there are interactions between pressureless matter as well as dark energy. We construct the corresponding autonomous system of equations to check the stability of the model for non phantom, vacuum and phantom phases. It is concluded that critical points remain more stable in phantom phase as compared to non phantom and vacuum cases. Finaily, we discuss the cosmological behavior of the model through some cosmological parameters.

关键词： f(T) gravity LRS Bianchi type I universe phase space analysis

Dark Energy models and Cosmic Acceleration with Anisotropic Universe in f(T) Gravity

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Communications in Theoretical Physics 2014年第4期61卷 482-490页

作者： m.sharif Sehrish Azeem Department of mathematics University of the PunjabQuaid-e-Azam Campus

This paper is devoted to studing the accelerated expansion of the universe in context of f（T） theory of gravity. For this purpose, we construct different f（T） models and investigate their cosmological behavior through equation of state parameter by using holographic, new agegraphic and their power-law entropy corrected dark energy models. We discuss the graphical behavior of this parameter versus redshif~ for particular values of constant parameters in Bianchi type I universe model. It is shown that the universe lies in different forms of dark energy, namely quintessence, phantom, and quintom corresponding to the chosen scale factors, which depend upon the constant parameters of the models.

关键词： f(T) gravity equation of state dark energy models

Shearfree Spherically Symmetric Fluid models

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Chinese Physics Letters 2012年第5期29卷 41-44页

作者： m.sharif Z.Yousaf Department of mathematics University of the PunjabQuaid-e-Azam CampusLahore-54590Pakistan

We attempt to discover some exact analytical models of the spherically symmetric spacetime of collapsing fluid under shearfree *** types of solution are considered:one is to impose a condition on the mass function,while the other is to restrict the *** obtain five exact models in total,and some of them satisfy the Darmoie conditions.

关键词： conditions. exact satisfy