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Mubasher Jamil

Publications and source records attributed to Mubasher Jamil.

At least 199 records · Page 11Linked to original sources
arXiv2010

Holographic dark energy with varying gravitational constant in Horava-Lifshitz cosmology

We investigate the holographic dark energy scenario with a varying gravitational constant in a flat background in the context of Hořava-Lifshitz gravity. We extract the exact differential equation determining the evolution of the dark energy density parameter, which includes $G$ variation term. Also we discuss a cosmological implication of our work by evaluating the dark energy equation of state for low redshifts containing varying $G$ corrections.

hep-th↗
arXiv2009

Black Holes in Bulk Viscous Cosmology

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.

astro-ph↗
arXiv2009

Primordial Black Holes in Phantom Cosmology

We investigate the effects of accretion of phantom energy onto primordial black holes. Since Hawking radiation and phantom energy accretion contribute to a {\it decrease} of the mass of the black hole, the primordial black hole that would be expected to decay now due to the Hawking process would decay {\it earlier} due to the inclusion of the phantom energy. Equivalently, to have the primordial black hole decay now it would have to be more massive initially. We find that the effect of the phantom energy is substantial and the black holes decaying now would be {\it much} more massive -- over 10 orders of magnitude! This effect will be relevant for determining the time of production and hence the number of evaporating black holes expected in a universe accelerating due to phantom energy.

gr-qc↗
arXiv2009

Wormhole Thermodynamics at Apparent Horizons

In this paper, we discuss the thermodynamic properties of the evolving Lorentzian wormhole. For the shape function $b(r) = r_{0}^2/r$, it is shown that the wormhole spacetime admits two apparent horizons, the inner and the outer one. The inner horizon expands while the outer contracts with the passage of time. Corresponding to these horizons, we have three types of wormholes, regular, extreme and the naked wormholes. Moreover, it is shown that the Einstein field equations can be rewritten as a first law of thermodynamics $dE=TdS+WdV$, at the apparent horizons of the wormhole, where $E=ρV$, $T = κ/2π$, $S=A/4G$, $W=(ρ-P)/2$ and $V = {4/3}π\tilde{r}_{A+}^3$ are the total matter energy, horizon temperature, wormhole entropy, work density and the volume of the wormhole respectively.

hep-th↗
arXiv2009

On the resolution of cosmic coincidence problem and phantom crossing with triple interacting fluids

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.

gr-qc↗
arXiv2009

Interacting new generalized Chaplygin gas

We have presented a model in which the new generalized Chaplygin gas interacts with matter. We find that there exists a stable scaling solution at late times in the evolution of the universe. Moreover, the phantom crossing scenario is observed in this model.

gr-qc↗
arXiv2009

On the role of pressure anisotropy for relativistic stars admitting conformal motion

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] $p_t - p_r = \frac{1}{8 π}(\frac{c_1}{r^2} + c_2)$ where, n, $c_1$ and $c_2$ are arbitrary constants. The solutions yield expressions of the physical quantities like pressure gradients and the mass.

astro-ph↗
arXiv2009

Interacting Holographic Viscous Dark Energy Model

In this manuscript, we present a generalization of the interacting holographic dark energy model using the viscous generalized Chaplygin gas. We also study the model by considering a dynamical Newton's constant $G$. Then we reconstruct the potential and the dynamics of the scalar field which describe the viscous Chaplygin cosmology.

gr-qc↗
arXiv2009

Black Holes in Accelerated Universe

We have analyzed the evolution of mass of a stationary black hole in the standard FRW cosmological model. The evolution is determined specifically about the time of transition from the earlier matter to the later exotic dark energy dominated universe. It turns out that the accretion rate of matter on the black hole of mass $M$ was approximately $10^{54}M^{-1}$ higher than the accretion rate of exotic dark energy at the time of transition.

astro-ph↗
arXiv2009

On generating some known black hole solutions

In this paper, we have presented an algorithm to generate various black hole solutions in general relativity and alternative theories of gravity. The algorithm involves few dimensional parameters that are assigned suitable values to specify the required black hole.

gr-qc↗
arXiv2009

Evolution of a Schwarzschild Black Hole in Phantom-like Chaplygin gas Cosmologies

In the classical relativistic regime, the accretion of phantom energy onto a black hole reduces the mass of the black hole. In this context, we have investigated the evolution of a Schwarzschild black hole in the standard model of cosmology using the phantom-like modified variable Chaplygin gas and the viscous generalized Chaplygin gas. The corresponding expressions for accretion time scale and evolution of mass have been derived. Our results indicate that mass of the black hole will decrease if the accreting phantom Chaplygin gas violates the dominant energy condition and will increase in the opposite case. Thus our results are in agreement with the results of Babichev \textit{et al} \cite{Babi1} who first proposed this scenario.

gr-qc↗
arXiv2009

Holographic dark energy with varying gravitational constant

We investigate the holographic dark energy scenario with a varying gravitational constant, in flat and non-flat background geometry. We extract the exact differential equations determining the evolution of the dark energy density-parameter, which include $G$-variation correction terms. Performing a low-redshift expansion of the dark energy equation of state, we provide the involved parameters as functions of the current density parameters, of the holographic dark energy constant and of the $G$-variation.

hep-th↗
arXiv2009

Generalized Holographic Dark Energy Model

In this paper, the model of holographic Chaplygin gas has been extended to two general cases: first is the case of modified variable Chaplygin gas and secondly of the viscous generalized Chaplygin gas. The dynamics of the model are expressed by the use of scalar fields and the scalar potentials.

gr-qc↗
arXiv2009

Cosmic coincidence problem and variable constants of physics

The standard model of cosmology is investigated using time dependent cosmological constant $Λ$ 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 $ω\to-1$, with minute fluctuations, showing an evolving $ω$. Thus our model fairly alleviates the cosmic coincidence problem which demands $ω=-1$ at present time.

gr-qc↗
arXiv2009

Constraints on coupling constant between dark energy and dark matter

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 $0<c<1$ on the coupling constant occurs as a very special case. Our analysis also supports the existence of phantom energy under certain conditions on the coupling constant.

astro-ph↗
arXiv2009

Wormholes supported by phantom-like modified Chaplygin gas

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.

gr-qc↗