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Mubasher Jamil

Publications and source records attributed to Mubasher Jamil.

At least 145 records · Page 8Linked to original sources
arXiv2011

Power-law entropy-corrected HDE and NADE in Brans-Dicke cosmology

Considering the power-law corrections to the black hole entropy, which appear in dealing with the entanglement of quantum fields inside and outside the horizon, the holographic energy density is modified accordingly. In this paper we study the power-law entropy-corrected holographic dark energy in the framework of Brans-Dicke theory. We investigate the cosmological implications of this model in detail. We also perform the study for the new agegraphic dark energy model and calculate some relevant cosmological parameters and their evolution. {As a result we find that this model can provide the present cosmic acceleration and even the equation of state parameter of this model can cross the phantom line $w_D=-1$ provided the model parameters are chosen suitably}.

astro-ph.CO↗
arXiv2011

Evolution of Primordial Black Holes in Loop Quantum Gravity

In this work, we study the evolution of Primordial Black Holes within the context of Loop Quantum Gravity. First we calculate the scale factor and energy density of the universe for different cosmic era and then taking these as inputs we study evolution of primordial black holes. From our estimation it is found that accretion of radiation does not affect evolution of primordial black holes in loop quantum gravity even though a larger number of primordial black holes may form in early universe in comparison with Einstein's or scalar-tensor theories.

gr-qc↗
arXiv2011

Non-equilibrium thermodynamics of dark energy on the power-law entropy corrected apparent horizon

We investigate the Friedmann-Robertson-Walker (FRW) universe (containing dark energy) as a non-equilibrium (irreversible) thermodynamical system by considering the power-law correction to the horizon entropy. By taking power-law entropy area law which appear in dealing with the entanglement of quantum fields in and out the horizon, we determine the power-law entropy corrected apparent horizon of the FRW universe.

physics.gen-ph↗
arXiv2011

Holographic dark energy in Brans-Dicke theory with log correction

In the derivation of holographic dark energy density, the area law of the black hole entropy plays a crucial role. However, the entropy-area relation can be modified from the inclusion of quantum effects, motivated from the loop quantum gravity, string theory and black hole physics. In this paper, we study cosmological implication of the interacting entropy-corrected holographic dark energy model in the framework of Brans-Dicke cosmology. We obtain the equation of state and the deceleration parameters of the entropy-corrected holographic dark energy in a non-flat Universe. As system's IR cutoff we choose the radius of the event horizon measured on the sphere of the horizon, defined as $L=ar(t)$. We find out that when the entropy-corrected holographic dark energy is combined with the Brans-Dicke field, the transition from normal state where $w_D >-1 $ to the phantom regime where $w_D <-1 $ for the equation of state of interacting dark energy can be more easily achieved for than when resort to the Einstein field equations is made.

physics.gen-ph↗
arXiv2011

Holographic dark energy in Brans-Dicke cosmology with Granda-Oliveros cut-off

Motivated by the recent works of one of us [1,2] we study the holographic dark energy in Brans-Dicke gravity with the Granda-Oliveros cut-off proposed recently in literature. We find out that when the present model is combined with Brans-Dicke field the transition from normal state where $w_D >-1 $ to the phantom regime where $w_D <-1 $ for the equation of state of dark energy can be more easily achieved for than when resort to the Einstein field equations is made. Furthermore, the phantom crossing is more easily achieved when the matter and the holographic dark energy undergo an exotic interaction. We also calculate some relevant cosmological parameters and their evolution.

physics.gen-ph↗
arXiv2011

Statefinder Parameter for Varying G in Three Fluid System

In this work, we have considered variable G in flat FRW universe filled with the mixture of dark energy, dark matter and radiation. If there is no interaction between the three fluids, the deceleration parameter and statefinder parameters have been calculated in terms of dimensionless density parameters which can be fixed by observational data. Also the interaction between three fluids has been analyzed due to constant $G$. The statefinder parameters also calculated in two cases: pressure is constant and pressure is variable.

physics.gen-ph↗
arXiv2011

Modified Chaplygin Gas and Solvable F-essence Cosmologies

The Modified Chaplygin Gas (MCG) model belongs to the class of a unified models of dark energy and dark matter. In this paper, we have modeled MCG in the framework of f-essence cosmology. By constructing an equation connecting the MCG and the f-essence, we solve it to obtain explicitly the pressure and energy density of MCG. As special cases, we obtain both positive and negative pressure solutions for suitable choices of free parameters. We also calculate the state parameter which describes the phantom crossing.

physics.gen-ph↗
arXiv2011

Fractional Action Cosmology: Some Dark Energy Models in Emergent, Logamediate and Intermediate Scenarios of the Universe

In the framework of Fractional Action Cosmology, we have reconstructed the scalar potentials and scalar fields, namely, quintessence, phantom, tachyon, k-essence, DBI-essence, Hessence, dilaton field and Yang-Mills field. To get more physical picture of the variation of the scalar field and potential with time, we express scale factor in emergent, logamediate and intermediate scenarios, under which the Universe expands differently.

physics.gen-ph↗
arXiv2011

Fractional Action Cosmology: Emergent, Logamediate, Intermediate, Power law Scenarios of the Universe and Generalized Second Law of Thermodynamics

In the framework of Fractional Action Cosmology (FAC), we study the generalized second law of thermodynamics for the Friedmann Universe enclosed by a boundary. We use the four well-known cosmic horizons as boundaries namely, apparent horizon, future event horizon, Hubble horizon and particle horizon. We construct the generalized second law (GSL) using and without using the first law of thermodynamics. To check the validity of GSL, we express the law in the form of four different scale factors namely emergent, logamediate, intermediate and power law. For Hubble, apparent and particle horizons, the GSL holds for emergent and logamediate expansions of the universe when we apply with and without using first law. For intermediate scenario, the GSL is valid for Hubble, apparent, particle horizons when we apply with and without first law. Also for intermediate scenario, the GSL is valid for event horizon when we apply first law but it breaks down without using first law. But for power law expansion, the GSL may be valid for some cases and breaks down otherwise.

physics.gen-ph↗
arXiv2011

Cosmic Evolution in Brans-Dicke Chameleon Cosmology

We have investigated the Brans-Dicke Chameleon theory of gravity and obtained exact solutions of the scale factor $a(t)$, scalar field $ϕ(t)$, an arbitrary function $f(ϕ)$ which interact with the matter Lagrangian in the action of the Brans-Dicke Chameleon theory and potential $V(ϕ)$ for different epochs of the cosmic evolution. We plot the functions $a(t)$, $ϕ(t)$, $f(t)$ and $V(ϕ)$ for different values of the Brans-Dicke parameter. In our models, there is no accelerating solution, only decelerating one with $q>0$. The physical cosmological distances have been investigated carefully. Further the statefinder parameters pair and deceleration parameter are discussed.

physics.gen-ph↗
arXiv2011

Noether Symmetry Approach in f(R) Tachyon Model

In this Letter by utilizing the Noether symmetry approach in cosmology, we attempt to find the tachyon potential via the application of this kind of symmetry to a flat Friedmann-Robertson-Walker (FRW) metric. We reduce the system of equations to simpler ones and obtain the general class of the tachyon's potential function and $f(R)$ functions. We have found that the Noether symmetric model results in a power law $f(R)$ and an inverse fourth power potential for the tachyonic field. Further we investigate numerically the cosmological evolution of our model and show explicitly the behavior of the equation of state crossing the cosmological constant boundary.

physics.gen-ph↗
arXiv2011

Notes on dark energy interacting with dark matter and unparticle in loop quantum cosmology

We investigate the behavior of dark energy interacting with dark matter and unparticle in the framework of loop quantum cosmology. In four toy models, we study the interaction between the cosmic components by choosing different coupling functions representing the interaction. We found that there are only two attractor solutions namely dark energy dominated and dark matter dominated Universe. The other two models are unstable, as they predict either a dark energy filled Universe or one completely devoid of it.

physics.gen-ph↗
arXiv2011

Noether Gauge Symmetry Approach in f(R) Gravity

We discuss the f(R) gravity model in which the origin of dark energy is identified as a modification of gravity. The Noether symmetry with gauge term is investigated for the f(R) cosmological model. By utilization of the Noether Gauge Symmetry (NGS) approach, we obtain two exact forms f(R) for which such symmetries exist. Further it is shown that these forms of f(R) are stable.

physics.gen-ph↗
arXiv2011

Effect of Vacuum Energy on Evolution of Primordial Black Holes in Einstein Gravity

We study the evolution of primordail black holes by considering present universe is no more matter dominated rather vacuum energy dominated. We also consider the accretion of radiation, matter and vacuum energy during respective dominance period. In this scenario, we found that radiation accretion efficiency should be less than 0.366 and accretion rate is much larger than previous analysis by B. Nayak et al. \cite{ns}. Thus here primordial black holes live longer than previous works \cite{ns}. Again matter accretion slightly increases the mass and lifetime of primordial black holes. However, the vacuum energy accretion is slightly complicated one, where accretion is possible only upto a critical time. This critical time depends on the values of accretion efficiency and formation time. If a primordial black hole lives beyond critical time, then its lifespan increases due to vacuum energy accretion. But for presently evaporating primordial black holes, critical time comes much later than their evaporating time and thus vacuum energy could not affect those primordial black holes. We again found that the constraints on the initial mass fraction of PBH obtained from the $γ$-ray background limit becomes stronger in the presence of vacuum energy.

gr-qc↗
arXiv2011

Quantum Corrections for a Braneworld Black Hole

By using the quantum tunneling approach over semiclassical approximations, we study the quantum corrections to the Hawking temperature, entropy and Bekenstein-Hawking entropy-area relation for a black hole lying on a brane.

gr-qc↗
arXiv2011

Restoring New Agegraphic Dark Energy in RS II Braneworld

Motivated by recent works [1,2], we investigate new agegraphic model of dark energy in the framework of RS II braneworld. We also include the case of variable gravitational constant in our model. Furthermore, we establish correspondence between the new agegraphic dark energy with other dark energy candidates based on scalar fields.

physics.gen-ph↗
arXiv2011

Thermodynamics of phantom energy in the presence of a Reissner-Nordstrom black hole

In this paper, we study the validity of the generalized second law (GSL) in phantom dominated universe in the presence of a Reissner-Nordström (RN) black hole. Our study is independent of the origin of the phantom like behavior of the considered universe. We also discuss the GSL in the neighborhood of transition from quintessence to phantom regime. We show that for a constant equation of state parameter, the GSL may be satisfied provided that the temperature is proportional to de Sitter temperature. It is shown that in models with (only) a transition from quintessence to phantom regime the generalized second law does not hold in the transition epoch. Next we show that if the phantom energy has a chemical potential, then the GSL will hold if the mass of black hole is above from a critical value.

physics.gen-ph↗