Showing papers by "Mubasher Jamil published in 2008"
TL;DR: In the classical relativistic regime, the accretion of phantom-like dark energy onto a stationary black hole reduces the mass of the black hole as mentioned in this paper, and this condition restricts the mass-to-charge ratio in a narrow range.
Abstract: In the classical relativistic regime, the accretion of phantom-like dark energy onto a stationary black hole reduces the mass of the black hole. We have investigated the accretion of phantom energy onto a stationary charged black hole and have determined the condition under which this accretion is possible. This condition restricts the mass-to-charge ratio in a narrow range. This condition also challenges the validity of the cosmic-censorship conjecture since a naked singularity is eventually produced due to accretion of phantom energy onto black hole.
120 citations
TL;DR: In this article, a unified model of dark energy and matter was presented using the modified variable Chaplygin gas for interacting dark energy in a non-flat universe, which involves a coupling constant.
Abstract: A unified model of dark energy and matter is presented using the modified variable Chaplygin gas for interacting dark energy in a non-flat universe. The two entities interact with each other non-gravitationally, which involves a coupling constant. Due to dynamic interaction, a variation in this constant arises that henceforth changes the equations of state of these quantities. We have derived the effective equations of state corresponding to matter and dark energy in this interacting model. Moreover, the case of phantom energy is deduced by putting constraints on the parameters involved.
108 citations
TL;DR: In the classical relativistic regime, the accretion of phantom-like dark energy onto a stationary black hole reduces the mass of the black hole by a narrow limit as mentioned in this paper.
Abstract: In the classical relativistic regime, the accretion of phantom-like dark energy onto a stationary black hole reduces the mass of black hole. Here we have investigated the accretion of phantom energy onto a stationary charged black hole and have determined the condition under which this accretion is possible. This condition restricts the mass to charge ratio in a narrow limit. This condition also challenges the validity of the cosmic censorship conjecture since a naked singularity is eventually produced as magnitude of charge increases compared to mass of black hole.
100 citations
TL;DR: In this article, the authors investigated the model of dark energy interacting with dark matter by choosing inhomogeneous equations of state for the dark energy and a nonlinear interaction term for the underlying interaction.
Abstract: We have investigated the model of dark energy interacting with dark matter by choosing inhomogeneous equations of state for the dark energy and a nonlinear interaction term for the underlying interaction. The equations of state have dependencies either on the energy densities, the redshift, the Hubble parameter or the bulk viscosity. We have considered these possibilities and have derived the effective equations of state for the dark energy in each case.
93 citations
TL;DR: In this paper, a unified model of dark energy and matter was presented using the modified variable Chaplygin gas for interacting dark energy in a non-flat universe, where the two entities interact with each other non-gravitationally which involves a coupling constant.
Abstract: A unified model of dark energy and matter is presented using the modified variable Chaplygin gas for interacting dark energy in a non-flat universe. The two entities interact with each other non-gravitationally which involves a coupling constant. Due to dynamic interaction, the variation in this constant arises that henceforth changes the equations of state of these quantities. We have derived the effective equations of state corresponding to matter and dark energy in this interacting model. Moreover, the case of phantom energy is deduced by putting constraints on the parameters involved.
90 citations
TL;DR: In this article, the authors investigated constraints on the coupling between dark matter and the interacting Chaplygin gas and showed that the coupling constant between these two entities can take arbitrary values, which can be either positive or negative.
Abstract: We have investigated constraints on the coupling between dark matter and the interacting Chaplygin gas. Our results indicate that the coupling constant $c$ between these two entities can take arbitrary values, which can be either positive or negative, thus giving arbitrary freedom to the inter-conversion between Chaplygin gas and dark matter. Thus our results indicate that the restriction $0
74 citations
TL;DR: In this article, the authors examined the possible construction of a stationary, spherically symmetric and spatially inhomogeneous wormhole spacetime supported by the phantom energy, which is represented by the modified Chaplygin gas equation of state.
Abstract: We have examined the possible construction of a stationary, spherically symmetric and spatially inhomogeneous wormhole spacetime supported by the phantom energy. The later is supposed to be represented by the modified Chaplygin gas equation of state. The solutions so obtained satisfy the flare out and the asymptotic flatness conditions. It is also shown that the averaged null energy condition has to be violated for the existence of the wormhole.
43 citations
TL;DR: In this article, a modified Chaplygin gas equation of state was used to model the cosmological constants and Newton's gravitational constant in the standard model of cosmology, and it was found that the time dependent constants coupled with the modified Chapleygin gas interpolate between the earlier matter to the later dark energy dominated phase of the universe.
Abstract: The standard model of cosmology is investigated using time dependent cosmological constant $\Lambda$ and Newton's gravitational constant $G$. The total energy content is described by the modified Chaplygin gas equation of state. It is found that the time dependent constants coupled with the modified Chaplygin gas interpolate between the earlier matter to the later dark energy dominated phase of the universe. We also achieve a convergence of parameter $\omega\to-1$, with minute fluctuations, showing an evolving $\omega$. Thus our model fairly alleviates the cosmic coincidence problem which demands $\omega=-1$ at present time.
35 citations
TL;DR: In this paper, the spacetime of anisotropic stars admitting conformal motion is investigated, and the Einstein field equations are solved using different ansatz of the surface tension, yielding expressions of the physical quantities like pressure gradients and the mass.
Abstract: We investigate the spacetime of anisotropic stars admitting conformal motion. The Einstein field equations are solved using different ansatz of the surface tension. In this investigation, we study two cases in details with the anisotropy as: [1] $p_t = n p_r$ [2] $p_t - p_r = \frac{1}{8 \pi}(\frac{c_1}{r^2} + c_2)$ where, n, $c_1$ and $c_2$ are arbitrary constants. The solutions yield expressions of the physical quantities like pressure gradients and the mass.
30 citations
Posted Content•
08 Feb 2008
TL;DR: In this paper, the authors investigated constraints on the coupling between dark matter and the interacting Chaplygin gas and showed that the coupling constant between these two entities can take arbitrary values, which can be either positive or negative.
Abstract: We have investigated constraints on the coupling between dark matter and the interacting Chaplygin gas. Our results indicate that the coupling constant $c$ between these two entities can take arbitrary values, which can be either positive or negative, thus giving arbitrary freedom to the inter-conversion between Chaplygin gas and dark matter. Thus our results indicate that the restriction $0
11 citations
TL;DR: In this paper, the authors investigate the model of interacting dark energy in the context of five dimensional brane cosmology and evaluate the effective equations of state of dark energy for various choices of the variable time dependent cosmological constant.
Abstract: We here investigate the model of interacting dark energy in the context of five dimensional brane cosmology. The effective equations of state of dark energy are evaluated for various choices of the variable time dependent cosmological constant. We have found that the interacting dark energy obeys the phantom divide/crossing scenario in this generalized model. It is also shown that interacting dark energy in this generalized model also resolves the cosmic coincidence problem.
TL;DR: In this paper, the authors investigated a cosmological model in which three fluids interact with each other involving certain coupling parameters and energy exchange rates and determined the conditions under triple interacting fluids will cross the phantom divide.
Abstract: We here investigate a cosmological model in which three fluids interact with each other involving certain coupling parameters and energy exchange rates. The motivation of the problem stems from the puzzling `triple coincidence problem' which naively asks why the cosmic energy densities of matter, radiation and dark energy are almost of the same order of magnitude at the present time. In our model, we determine the conditions under triple interacting fluids will cross the phantom divide.
TL;DR: In this article, the authors investigate the effects of the accretion of phantom energy with non-zero bulk viscosity onto a Schwarzschild black hole and show that black holes accreting viscous phantom energy will lose mass rapidly compared to the non-viscous case.
Abstract: We investigate the effects of the accretion of phantom energy with non-zero bulk viscosity onto a Schwarzschild black hole and show that black holes accreting viscous phantom energy will lose mass rapidly compared to the non-viscous case. When matter is incorporated along with the phantom energy, the black holes meet with the same fate as bulk viscous forces dominate matter accretion. If the phantom energy has large bulk viscosity, then the mass of the black hole will reduce faster than in the small viscosity case.
Posted Content•
09 Oct 2008
TL;DR: In this article, the authors examined the problem of the gravitational collapse using higher dimensional Husain spacetime for the null fluid and the resulting mass evolution is discussed for each case, and the equations of state chosen to solve the field equations contain linear, quadratic and arbitrary powers of the radial parameter.
Abstract: We examine the problem of the gravitational collapse using higher dimensional Husain spacetime for the null fluid. The equations of state chosen to solve the field equations contain linear, quadratic and arbitrary powers of the radial parameter. The resulting mass evolution is discussed for each case.
TL;DR: In this paper, a mathematically consistent solution of the coupled Einstein-Maxwell equations for a slowly rotating neutron star is presented, which is also physically consistent as it remains finite in the no rotation limit, whereas Mirza's solution diverges for zero rotation.
Abstract: B.M. Mirza \cite{1} presented a solution of coupled Einstein-Maxwell equations for a slowly rotating neutron star; however his derivations had some errors and implicit assumptions that rendered the solution invalid. We point out the errors and present a mathematically consistent solution. The resulting solution is also physically consistent as it remains finite in the no rotation limit, whereas Mirza's solution diverges for zero rotation.
TL;DR: In this paper, the authors investigated the effects of the accretion of phantom energy with non-zero bulk viscosity onto a Morris-Thorne wormhole and found that if the bulk viscosity is large then the mass of wormhole increases rapidly as compared to small or zero bulk viscous energy.
Abstract: We investigate the effects of the accretion of phantom energy with non-zero bulk viscosity onto a Morris-Thorne wormhole. We have found that if the bulk viscosity is large then the mass of wormhole increases rapidly as compared to small or zero bulk viscosity.
Posted Content•
TL;DR: In this paper, the authors examined the problem of the gravitational collapse using higher dimensional Husain spacetime for the null fluid and the resulting mass evolution is discussed for each case, and the equations of state chosen to solve the field equations contain linear, quadratic and arbitrary powers of the radial parameter.
Abstract: We examine the problem of the gravitational collapse using higher dimensional Husain spacetime for the null fluid. The equations of state chosen to solve the field equations contain linear, quadratic and arbitrary powers of the radial parameter. The resulting mass evolution is discussed for each case.
TL;DR: In this article, the authors considered the possibility of a slowly rotating wormhole surrounded by a cloud of charged particles and determined the strength of this electromagnetic field and the corresponding flux of radiation.
Abstract: We have considered the possibility of a slowly rotating wormhole surrounded by a cloud of charged particles. Due to slow rotation of the wormhole, the charged particles are dragged thereby producing an electromagnetic field. We have determined the strength of this electromagnetic field and the corresponding flux of radiation.
TL;DR: In this paper, the authors investigated the model of dark energy interacting with dark matter by choosing inhomogeneous equations of state for dark energy and a non-linear interaction term for the underlying interaction.
Abstract: We have investigated the model of dark energy interacting with dark matter by choosing inhomogeneous equations of state for dark energy and a non-linear interaction term for the underlying interaction. The equation of state have dependencies either on the energy densities, redshift, Hubble parameter and its derivatives or the bulk viscosity. We have considered these possibilities and have derived the effective equations of state for the dark energy in each case.