arXiv subjects

Abdul Jawad

Publications and source records attributed to Abdul Jawad.

At least 37 records · Page 2Linked to original sources

arXiv2018

$f(T)$ Corrected Instability of Cylindrical Collapsing Object with Harrison-Wheeler Equation of State

In this paper, we study the dynamical instability of a collapsing object in the framework of generalized teleparallel gravity. We assume a cylindrical object with a specific matter distribution. This distribution contains energy density, isotropic pressure component with heat conduction. We take oscillating states scheme up to first order to check the instable behavior of the object. We construct a general collapse equation for underlying case with non-diagonal tetrad depending on the matter, metric functions, heat conducting term and torsional terms. The Harrison-Wheeler equation of state which contains adiabatic index is used to explore the dynamical instability ranges for Newtonian and post-Newtonian constraints. These ranges depend on perturbed part of metric coefficients, matter parts and torsion.

physics.gen-ph↗

arXiv2018

Thermodynamics of Ricci-Gauss-Bonnet Dark Energy

We investigate the validity of generalized second law of thermodynamics of a physical system comprising of newly proposed dark energy model called Ricci Gauss-Bonnet and cold dark matter enveloped by apparent horizon and event horizon in flat Friedmann-Robertson-Walker (FRW) universe. For this purpose, Bekenstein entropy, Renyi, logarithmic and power law entropic corrections are used. It is found that this law exhibits the validity on both apparent and event horizons except for the case of logarithmic entropic correction at apparent horizon. Also, we check the thermodynamical equilibrium condition for all cases of entropy and found its vitality in all cases of entropy.

gr-qc↗

arXiv2018

Thermodynamics of Gravitationally Induced Particle Creation Scenario in DGP Braneworld

In this paper, we discuss the thermodynamical analysis for gravitationally induced particle creation scenario in the framework of DGP braneworld model. For this purpose, we consider apparent horizon as the boundary of the universe. We take three types of entropy such as Bakenstein entropy, logarithmic corrected entropy and power law corrected entropy with ordinary creation rate $Γ$. We analyze the first law and generalized second law of thermodynamics analytically for these entropies which hold under some constraints. The behavior of total entropy in each case is also discussed which implies the validity of generalized second law of thermodynamics. Also, we check the thermodynamical equilibrium condition for two phases of creation rate, that is constant and variable $Γ$ and found its validity in all cases of entropy.

physics.gen-ph↗

arXiv2017

Dynamics of Polynomial Chaplygin Gas Warm Inflation

In the present work, we study the consequences of considering a recently proposed polynomial inflationary potential in the context of the generalized, modified, and generalized cosmic Chaplygin gas models. In addition, we consider dissipative effects by coupling the inflation field to radiation, i.e., the inflationary dynamics is studied in the warm inflation scenario. We take into account a general parametrization of the dissipative coefficient $Γ$ for describing the decay of the inflaton field into radiation. By studying the background and perturbative dynamics in the weak and strong dissipative regimes of warm inflation separately for the positive and negative quadratic and quartic potentials, we obtain expressions for the most relevant inflationary observables as the scalar power spectrum, the scalar spectral, and the tensor-to-scalar ratio. We construct the trajectories in the $n_s-r$ plane for several expressions of the dissipative coefficient and compare with the two-dimensional marginalized contours for ($n_s,r$) from the latest Planck data. We find that our results are in agreement with WMAP9 and Planck 2015 data.

gr-qc↗

arXiv2017

Impact of generalized dissipative coefficient on warm inflationary dynamics in the light of latest Planck data

The warm inflation scenario in view of the modified Chaplygin gas is studied. We consider the inflationary expansion is driven by a standard scalar field whose decay ratio $Γ$ has a generic power law dependence with the scalar field $ϕ$ and the temperature of the thermal bath $T$. By assuming an exponential power law dependence in the cosmic time for the scale factor $a(t)$, corresponding to the intermediate inflation model, we solve the background and perturbative dynamics considering that our model evolves according to (i) weak dissipative regime and (ii) strong dissipative regime. Specifically, we find explicit expressions for the dissipative coefficient, scalar potential, and the relevant inflationary observables as the scalar power spectrum, scalar spectral index, and tensor-to-scalar ratio. The free parameters characterizing our model are constrained by considering the essential condition for warm inflation, the conditions for the model evolves according to weak or strong dissipative regime, and the 2015 Planck results through the $n_s-r$ plane.

gr-qc↗

arXiv2017

Accreting Fluids onto Regular Black Holes Via Hamiltonian Approach

We investigate the accretion of test fluids onto regular black holes such as Kehagias-Sfetsos black hole and a regular black hole with Dagum Distribution Function. We analyze the accretion process when different test fluids are falling onto these regular black holes. The accreting fluid is being classified through equation of state according to features of regular black holes. The behavior of fluid flow and the existence of sonic points is being checked for these regular black holes. It is noted that three velocity depends on critical points and equation of state parameter on phase space.

gr-qc↗

arXiv2017

Tidal Forces in Kiselev Black Hole

The aim of this paper is to examine the tidal forces occurred in Kiselev black hole surrounded by radiation and dust fluids. It is noted that radial and angular component of tidal force change the sign between event and Cauchy horizons. We solve the geodesic deviation equation for radially free falling bodies toward Kiselev black holes. We explain the geodesic deviation vector graphically and point out the location of event and Cauchy horizons in it for specific values of radiation and dust parameter.

gr-qc↗

arXiv2017

Effects of Thermal Fluctuations on Non-minimal Regular Magnetic Black Hole

We analyze the effects of thermal fluctuations on a regular black hole (RBH) of non-minimal Einstein-Yang-Mill theory with gauge field of magnetic Wu-Yang type and a cosmological constant. We consider the logarithmic corrected entropy in order to analyze the thermal fluctuations corresponding to non-minimal RBH thermodynamics. In this scenario, we develop various important thermodynamical quantities such as entropy, pressure, specific heats, Gibb's free energy and Helmothz free energy. We investigate first law of thermodynamics in the presence of logarithmic corrected entropy and non-minimal RBH. We also discuss the stability of this RBH using various frameworks such as $γ$ factor (comprises of ratio of heat capacities), phase transition, grand canonical ensemble and canonical ensemble. It is observed that the non-minimal RBH becomes more globally and locally stable if we increase the value of cosmological constant.

gr-qc↗

arXiv2017

Dynamics of warm power-law plateau inflation with a generalized inflaton decay rate: predicctions and constraints after Planck 2015

In the present work we study the consequences of considering a new family of single-field inflation models, called power-law plateau inflation, in the warm inflation framework. We consider the inflationary expansion is driven by a standard scalar field with a decay ratio $Γ$ having a generic power-law dependence with the scalar field $ϕ$ and the temperature of the thermal bath $T$ given by $Γ(ϕ,T)=C_ϕ\,\frac{T^m}{ϕ^{m-1}}$. Assuming that our model evolves according to the strong dissipative regime, we study the background and perturbative dynamics, obtaining the most relevant inflationary observables as the scalar power spectrum, the scalar spectral index and its running, and the tensor-to-scalar ratio. The free parameters characterizing our model are constrained by considering the essential condition for warm inflation, the conditions for the model evolves according to the strong dissipative regime, and the 2015 Planck results through the $n_s-r$ plane. For completeness, we study the predictions in the $n_s-dn_s/d\ln k$ plane. The model is consistent with a strong dissipative dynamics and predicts values for the tensor-to-scalar ratio and for the running of the scalar spectral index consistent with current bounds imposed by Planck, and we conclude that the model is viable.

gr-qc↗

arXiv2017

Warm Modified Chaplygin Gas Shaft Inflation

In this paper, we examine the possible realization of a new family of inflation called "shaft inflation" by assuming the modified Chaplygin gas model and tachyon scalar field. We also consider the special form of dissipative coefficient as $Γ={a_0}\frac{T^{3}}{ϕ^{2 }}$ and calculate the various inflationary parameters in the scenario of strong and weak dissipative regimes. In order to examine the behavior of inflationary parameters, the planes of $n_s - ϕ,~n_s - r$ and $n_s - α_s$ (where $n_s,~α_s,~r$ and $ϕ$ represent spectral index, its running, tensor to scalar ratio and scalar field respectively) are being developed which lead to the constraints: $r< 0.11$, $n_s=0.96\pm0.025$ and $α_s =-0.019\pm0.025$. It is quite interesting that these results of inflationary parameters are compatible with BICEP$2$, WMAP $(7+9)$ and recent Planck data.

gr-qc↗

arXiv2016

Non-minimal Coupling of Torsion-matter Satisfying Null Energy Condition for Wormhole Solutions

We explore wormhole solutions in a non-minimal torsion-matter coupled gravity by taking an explicit non-minimal coupling between the matter Lagrangian density and an arbitrary function of torsion scalar. This coupling depicts the transfer of energy and momentum between matter and torsion scalar terms. The violation of null energy condition occurred through effective energy-momentum tensor incorporating the torsion-matter non-minimal coupling while normal matter is responsible for supporting the respective wormhole geometries. We consider energy density in the form of non-monotonically decreasing function along with two types of models. First model is analogous to curvature-matter coupling scenario, that is, torsion scalar with $T$-matter coupling while the second one involves a quadratic torsion term. In both cases, we obtain wormhole solutions satisfying null energy condition. Also, we find that the increasing value of coupling constant minimizes or vanishes the violation of null energy condition through matter.

gr-qc↗

arXiv2016

Dynamics of Modified Chaplygin Gas Inflation on the Brane with Bulk Viscous Pressure

We investigate the role of bulk viscous pressure on the warm inflationary modified Chaplygin gas in brane-world framework in the presence of standard scalar field. We assume the intermediate inflationary scenario in strong dissipative regime and constructed the inflaton, potential, entropy density, slow-roll parameters, scalar and tensor power spectra, scalar spectral index and tensor-to-scalar ratio. We develop various trajectories such as $n_s - N$, $n_s - r$ and $n_s - α_s$ (where $n_s$ is the spectral index, $α_s$ is the running of spectral index, $N$ is the number of e-folds and $r$ is tensor-to-scalar ratio) for variable as well as constant dissipation and bulk viscous coefficients at high dissipative regime. It is interesting to remark here that our results of these parameters are compatible with recent observational data such as WMAP $7+9$, BICEP$2$ and Planck data.

gr-qc↗

arXiv2016

Dynamics of Particles around Time Conformal Schwarzschild Black Hole

In this work, we present the new technique for discussing the dynamical motion of neutral as well as charged particles in the absence/presence of magnetic field around the time conformal Schwarzschild black hole. Initially, we find the numerical solutions of geodesics of Schwarzschild black hole and the time conformal Schwarzschild black hole. We observe that the Schwarzschild spacetime admits the time conformal factor $e^{εf(t)}$, where $f(t)$ is an arbitrary function and $ε$ is very small which causes the perturbation in the spacetimes. This technique also re-scale the energy content of spacetime. We also investigate the thermal stability, horizons and energy conditions corresponding time conformal Schwarzschild spacetime. Also, we examine the dynamics of neutral and charged particle around time conformal Schwarzschild black hole. We investigate the circumstances under which the particle can escape from vicinity of black hole after collision with another particle. We analyze the effective potential and effective force of particle in the presence of magnetic field with angular momentum graphically.

physics.gen-ph↗

arXiv2016

Viscous Chaplygin Gas Models as a Spherical Top-Hat Collapsing Fluids

We study the spherical top-hat collapse in Einstein gravity and loop quantum cosmology by taking the non-linear evolution of viscous modified variable chaplygin gas and viscous generalized cosmic chaplygin gas. We calculate the equation of state parameter, square speed of sound, perturbed equation of state parameter, perturbed square speed of sound, density contrast and divergence of peculiar velocity in perturbed region and discussed their behavior. It is observed that both chaplygin gas models support the spherical collapse in Einstein as well as loop quantum cosmology because density contrast remains positive in both cases and the perturbed equation of state parameter remains positive at the present epoch as well as near future. It is remarked here that these parameters provide the consistence results for both chaplygin gas models in both gravities.

gr-qc↗

arXiv2016

Dynamics of Particles Around a Regular Black Hole with Nonlinear Electrodynamics

We investigate the dynamics of a charged particle being kicked off from its circular orbit around a regular black hole by an incoming massive particle in the presence of magnetic field. The resulting escape velocity, escape energy and the effective potential is analyzed. It is shown that the presence of even a very weak magnetic field helps the charged particles in escaping the gravitational field of the black hole. Moreover the effective force acting on the particle visibly reduces with distance. Thus particle near the black hole will experience higher effective force as compared to when it is far away.

gr-qc↗

arXiv2016

Aspects of Some New Versions of Pilgrim Dark Energy in DGP Braneworld

The illustration of cosmic acceleration under two interacting dark energy models (pilgrim dark energy with Granda and Oliveros cutoff and its generalized ghost version) in DGP braneworld framework is presented. In the current scenario, the equation of state parameter, deceleration parameter, $ω_{D}-ω'_{D}$ plane and statefinder diagnosis are investigated. The equation state parameter behave-like phantom era of the universe. The deceleration parameter depicts the accelerated expansion of the universe in both models. The cosmological planes like $ω_{D}-ω'_{D}$ and statefinder corresponds to $Λ$CDM limit. To end, we remark that our results support to phenomenon of pilgrim dark energy and cosmic acceleration. Also, the results are consistent with observational data.

gr-qc↗

arXiv2016

Generalized Mattig's relation in Brans-Dicke-Rastall gravity

The Geodesic Deviation Equation is being studied in Brans-Dicke-Rastall gravity. We briefly discuss the Brans-Dicke-Rastall gravity and then construct GDE for FLRW metric. In this way, the obtained geodesic deviation equation will correspond to the Brans-Dicke-Rastall gravity. Eventually, we solve numerically the null vector GDE to obtain from Mattig relation, the deviation vector $η(z)$ and observer area distance $r_0(z)$ and compare the results with $Λ$CDM model.

gr-qc↗

arXiv2016

Dynamics of Warm Chaplygin Gas Inflationary Models With Quartic Potential

Warm inflationary universe models in the context of generalized chaplygin gas, modified chaplygin gas, generalized cosmic chaplygin gas are being studied. The dissipative coefficient of the form $Γ\propto T$, weak and strong dissipative regimes are being considered. We use quartic potential $\frac{λ_{*}ϕ^{4}}{4}$, which is ruled out by current data in cold inflation but in our models it is analyzed that it is in agreement with the WMAP$9$ and latest Planck data. In these scenarios, the power spectrum, spectral index, and tensor to scalar ratio are being examined under the slow roll approximation. We show the dependence of tensor scalar ratio $r$ on spectral index $n_{s}$ and observe that the range of tensor scalar ratio is $r<0.05$ in generalized chaplygin gas, $r<0.15$ in modified chaplygin gas, and $r<0.12$ in generalized cosmic chaplygin gas models. Our results are in agreement with recent observational data like WMAP$9$ and latest Planck data.

gr-qc↗