Searcharxiv⌕ Search

arXiv subjects

Abdul Jawad

Publications and source records attributed to Abdul Jawad.

At least 55 records · Page 3Linked to original sources
arXiv2016

Superresonance Phenomenon from Acoustic Black Holes in Neo-Newtonian theory

We explore the possibility of the acoustic analogue of a super-radiance like phenomenon, i.e., the amplification of a sound wave by reflection from the ergo-region of a rotating acoustic black hole in the fluid draining bathtub model in the presence of the pressure be amplified or reduced in agreement with the value of the parameter $\left(γ=1+ \frac{knρ_0^{n-1} }{c^2}\right)$. We remark that the interval of frequencies depend upon the neo-newtonian parameter $γ$\, ($\barΩ_H = \frac{2 }{1+γ}\;Ω_{H}$)\textbf{ and becomes narrow in this work}. As a consequence, the tuning of the neo-newtonian parameter $\left(γ=1+ \frac{knρ_0^{n-1} }{c^2}\right)$ changes the rate of loss of the acoustic black hole mass.

gr-qc↗
arXiv2016

Noncommutative Wormhole Solutions in Einstein Gauss-Bonnet Gravity

In this paper, we explore static spherically symmetric wormhole solutions in the framework of $n$-dimensional Einstein Gauss-Bonnet gravity. Our objective is to find out wormhole solutions that satisfy energy conditions. For this purpose, we consider two frameworks such as Gaussian distributed and Lorentzian distributed non-commutative geometry. Taking into account constant redshift function, we obtain solutions in the form of shape function. The fifth and sixth dimensional solutions with positive as well as negative Gauss-Bonnet coefficient are discussed. Also, we check the equilibrium condition for the wormhole solutions with the help of generalized Tolman-Oppenheimer-Volkov equation. It is interesting to mention here that we obtain fifth dimensional stable wormhole solutions in both distributions that satisfy the energy conditions.

physics.gen-ph↗
arXiv2016

Dynamical Instability of Cylindrically Symmetric Collapsing Star in Generalized Teleparallel Gravity

This paper is devoted to analyze the dynamical instability of a self-gravitating object undergoes to collapse process. We take the framework of generalized teleparallel gravity with cylindrically symmetric gravitating object. The matter distribution is represented by locally anisotropic energy-momentum tensor. We develop basic equations such as dynamical equations along with matching conditions and Harrison-Wheeler equation of state. By applying linear perturbation strategy, we construct collapse equation which is used to accomplish the instability ranges in Newtonian and post-Newtonian regimes. We find these ranges for isotropic pressure as well as reduce the results in general relativity. The unstable behavior depends on matter, metric, mass and torsion based terms.

gr-qc↗
arXiv2016

Dynamical Instability of Shear-free Collapsing Star in Extended Teleparallel Gravity

We study the spherically symmetric collapsing star in terms of dynamical instability. We take the framework of extended teleparallel gravity with non-diagonal tetrad, power-law form of model presenting torsion and matter distribution as non-dissipative anisotropic fluid. The vanishing shear scalar condition is adopted to search the insights of collapsing star. We apply first order linear perturbation scheme to metric, matter and $f(T)$ functions. The dynamical equations are formulated under this perturbation scheme to develop collapsing equation for finding dynamical instability limits in two regimes such as Newtonian and post-Newtonian. We obtain constraint free solution of perturbed time dependent part with the help of vanishing shear scalar. The adiabatic index exhibits the instability ranges through second dynamical equation which depend on physical quantities such as density, pressure components, perturbed parts of symmetry of star, etc. We also develop some constraints on positivity of these quantities and obtain instability ranges to satisfy the dynamical instability condition.

gr-qc↗
arXiv2016

Accretion onto Some Well-Known Regular Black Holes

In this work, we discuss the accretion onto static spherical symmetric regular black holes for specific choices of equation of state parameter. The underlying regular black holes are charged regular black hole using Fermi-Dirac Distribution, logistic distribution, nonlinear electrodynamics, respectively and Kehagias-Sftesos asymptotically flat regular black hole. We obtain the critical radius, critical speed and squared sound speed during the accretion process near the regular black holes. We also study the behavior of radial velocity, energy density and rate of change of mass for each regular black holes.

gr-qc↗
arXiv2015

Holographic polytropic $f(T)$-gravity models

The present paper reports a study on the cosmological consequences arising from reconstructing $f(T)$ gravity through new holographic-polytropic dark energy. We assume two approaches, namely a particular form of Hubble parameter $H$ and a solution for $f(T)$. We obtain the deceleration parameter, effective equation of state as well as torsion equation of state parameters from total density and pressure in both cases. It is interesting to mention here that the deceleration and torsion equation of state represent transition from deceleration to acceleration phase. We study the statefinder parameters under both approaches which result that statefinder trajectories are found to attain $Λ$CDM point. The comparison with observational data represents consistent results. Also, we discuss the stability of reconstructed models through squared speed of sound which represents stability in late times.

gr-qc↗
arXiv2015

Strange Stars in $f(T)$ Gravity With MIT Bag Model

This paper deals with existence of strange stars in $f\left(T\right) $ modified gravity. For this purpose, we have taken the diagonal tetrad field of static spacetime with charged anisotropic fluid and MIT bag model, which provide the linear relation between radial pressure and density of the matter. Further, the analysis of the resulting equations have been done by assuming the parametric form of the metric functions in term of the radial profiles with some unknown constant (introduced by Krori and Barua). By the matching of two metrices, unknown constant of the metric functions appear in terms of mass, radius and charge of the stars, the observed values of these quantities have been used for the detail analysis of the the derived model. We have discuss the regularity, anisotropy, energy conditions, stability and surface redshift of the model.

physics.gen-ph↗
arXiv2015

Lorentz Distributed Noncommutative Wormhole Solutions in Extended Teleparallel Gravity

In this paper, we study static spherically symmetric wormhole solutions in extended teleparallel gravity with the inclusion of noncommutative geometry under Lorentzian distribution. We obtain expressions of matter components for non-diagonal tetrad. The effective energy-momentum tensor leads to the violation of energy conditions which impose condition on the normal matter to satisfy these conditions. We explore the noncommutative wormhole solutions by assuming a viable power-law $f(T)$ and shape function models. For the first model, we discuss two cases in which one leads to teleparallel gravity and other is for $f(T)$ gravity. The normal matter violates the weak energy condition for first case while there exist a possibility for micro physically acceptable wormhole solution. There exist a physically acceptable wormhole solution for the power-law $b(r)$ model. Also, we check the equilibrium condition for these solutions which is only satisfied for teleparallel case while for $f(T)$ case, these solutions are less stable.

gr-qc↗
arXiv2015

Cosmological Analysis of Pilgrim Dark Energy in Loop Quantum Cosmology

The proposal of pilgrim dark energy is based on speculation that phantom-like dark energy (with strong enough resistive force) can prevent black hole formation in the universe. We explore this phenomenon in loop quantum cosmology framework by taking Hubble horizon as an infra-red cutoff in pilgrim dark energy. We evaluate the cosmological parameters such as Hubble, equation of state parameter, squared speed of sound and also cosmological planes like $ω_{\vartheta}-ω'_{\vartheta}$ and $r-s$ on the basis of pilgrim dark energy parameter ($u$) and interacting parameter ($d^2$). It is found that values of Hubble parameter lies in the range $74^{+0.005}_{-0.005}$. It is mentioned here that equation state parameter lies within the ranges $-1\mp0.00005$ for $u=2, 1$ and $(-1.12,-1), (-5,-1)$ for $u=-1,-2$, respectively. Also, $ω_{\vartheta}-ω'_{\vartheta}$ planes provide $Λ$CDM limit, freezing and thawing regions for all cases of $u$. It is also interesting to mention here that $ω_{\vartheta}-ω'_{\vartheta}$ planes lie in the range ($ω_{\vartheta}=-1.13^{+0.24}_{-0.25}, ω'_{\vartheta}<1.32$). In addition, $r-s$ planes also corresponds to $Λ$CDM for all cases of $u$. Finally, it is remarked that all the above constraints of cosmological parameters shows consistency with different observational data like Planck, WP, BAO, $H_0$ and SNLS.

gr-qc↗
arXiv2015

Holographic dark energy reconstruction of $f(T,\mathcal{T})$ gravity

The present paper reports a holographic reconstruction scheme for $f(T,\mathcal T)$ gravity proposed in Harko et al. $\emph{JCAP}\; 12(2014)021$ where $T$ is the torsion scalar and $\mathcal{T}$ is the trace of the energy-momentum tensor considering future event horizon as the enveloping horizon of the universe. We have considered $f(T, \mathcal T)=T + γg(\mathcal T)$ and $f(T,\mathcal T) =β\mathcal T + g(T)$ for reconstruction. We observe that the derived $f(T,\mathcal T)$ models can represent phantom or quintessence regimes of the universe which are compatible with the current observational data.

gr-qc↗
arXiv2014

Analysis of Generalized Ghost Pilgrim Dark Energy in Non-flat FRW Universe

This work is based on pilgrim dark energy conjecture which states that phantom-like dark energy possesses the enough resistive force to preclude the formation of black hole. The non-flat geometry is considered which contains the interacting generalized ghost pilgrim dark energy with cold dark matter. Some well-known cosmological parameters (evolution parameter ($ω_Λ$) and squared speed of sound) and planes ($ω_Λ$-$ω_Λ'$ and statefinder) are constructed in this scenario. The discussion of these parameters is totally done through pilgrim dark energy parameter ($u$) and interacting parameter ($d^2$). It is interesting to mention here that the analysis of evolution parameter supports the conjecture of pilgrim dark energy. Also, this model remains stable against small perturbation in most of the cases of $u$ and $d^2$. Further, the cosmological planes correspond to $Λ$CDM limit as well as different well-known dark energy models.

gr-qc↗
arXiv2014

Analysis of Generalized Ghost Version of Pilgrim Dark Energy

The proposal of pilgrim dark energy is based on the speculation that phantom-like dark energy possesses enough resistive force to preclude the black hole formation in the later universe. We explore this phenomenon by assuming the generalized ghost version of pilgrim dark energy. We find that most of the values of the interacting ($ξ^2$) as well as pilgrim dark energy ($u$) parameters push the equation of state parameter towards phantom region. The squared speed of sound shows that this model remains stable in most of the cases of $ξ^2$ and $u$. We also develop $ω_Λ-ω'_Λ$ plane and observe that this model corresponds to thawing as well as freezing regions. Finally, it is shown that the non-interacting and interacting generalized ghost versions of pilgrim dark energy correspond to $Λ$CDM limit on the statefinder plane.

gr-qc↗
arXiv2014

Pilgrim Dark Energy in $f(T, T_G)$ cosmology

We work on the reconstruction scenario of pilgrim dark energy" (PDE) in $f(T, T_G)$. In PDE model it is assumed that a repulsive force that is accelerating the Universe is phantom type with $(w_{DE}<-1)$ and it so strong that prevents formation of the black hole. We construct the $f(T, T_G)$ models and correspondingly evaluate equation of state parameter for various choices of scale factor. Also, we assume polynomial form of $f(T, T_G)$ in terms of cosmic time and reconstruct $H$ and $w_{DE}$ in this manner. Through discussion, it is concluded that PDE shows aggressive phantom-like behaviour for$s=-2$ in $f(T, T_G)$ gravity.

gr-qc↗
arXiv2014

Holographic reconstruction of $f(G)$ Gravity for scale factors pertaining to Emergent, Logamediate and Intermediate scenarios

In this paper, we reconstruct the holographic dark energy in the framework of $f(G)$ modified theory of gravity, where $G$ is Gauss-Bonnet invariant. In this context, we choose the infrared cut-off as Granda-Oliveros cut-off which is proportional to the Hubble parameter $H$ and its first derivative with respect to the cosmic time $t$. We reconstruct $f(G)$ model with the inclusion of HDE and three well-known forms of the scale factor $a(t)$, i.e. the emergent, the logamediate and the intermediate scale factors. The reconstructed model as well as equation of state parameter are discussed numerically with the help of graphical representation to explore the accelerated expansion of the universe. Moreover, the stability of the models incorporating all the scale factors is checked through squared speed of sound $v_s^2$.

gr-qc↗
arXiv2014

Reconstruction of $f(G)$ Gravity with New Agegraphic Dark Energy Model

In this work, we consider the reconstruction scenario of new agegraphic dark energy (NADE) model and $f(G)$ theory of gravity with $G$ representing the Gauss-Bonnet invariant in the flat FRW spacetime. In this context, we assume a solution of the scale factor in power-law form and study the correspondence scenario. A new agegraphic $f(G)$ model is constructed and discussed graphically for the evolution of the universe. Using this model, we investigate the different eras of the expanding universe and stability with the help of the equation of state (EoS) parameter $ω_{eff}$ and squared speed of sound $v_s^2$, respectively. It is mentioned here that the reconstructed model represents the quintessence era of the accelerated expansion of the universe with instability. Moreover, the statefinder trajectories are studied and we find out that the model is not capable of reaching the $Λ$CDM phase of the universe.

gr-qc↗
arXiv2013

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

This paper is devoted to study the modified holographic dark energy model by taking its different aspects in the flat Kaluza-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 all the results are consistent with the present observations.

gr-qc↗
arXiv2013

Thermodynamics in Closed Universe with Entropy Corrections

We discuss the generalized second law of thermodynamics in three different systems by taking quantum corrections (logarithmic and power law) to cosmological horizon entropy as well as black hole entropy. Firstly, we consider phantom energy accretion onto the Schwarzschild black hole in the closed FRW universe and investigate validity of the generalized second law of thermodynamics on the apparent and event horizons. In another scenario, we evaluate the critical mass of the Schwarzschild black hole with upper and lower bounds under accretion process due to phantom-like modified generalized chaplygin gas. It is found that the generalized second law of thermodynamics is respected within these bounds and black hole cannot accrete outside them. Finally, we explore this law for a closed universe filled with interacting $n$-components of fluid (in thermal equilibrium case) and with non-interacting dark matter and dark energy components (in thermal non-equilibrium case) on the apparent and event horizons and find conditions for its validity.

gr-qc↗