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Shamaila Rani

Publications and source records attributed to Shamaila Rani.

At least 19 recordsLinked to original sources
arXiv2024

Impact of $f(\mathcal{Q})$ Theory on the Stability of Compact Spherical Solutions

This research paper examines the feasibility and stability of compact stars in the context of $f(\mathcal{Q})$ theory, where $\mathcal{Q}$ represents the non-metricity scalar. To achieve this objective, a static spherical line element is assumed in the interior region and the Schwarzschild spacetime is used in the exterior region of the star. The unknown constants are determined by using the Darmois junction conditions. We consider a specific model of this theory to investigate the viability of compact stars through various physical quantities such as matter contents, energy bounds, anisotropy and state parameters. The stability states for the stellar objects under consideration are determined by the speed of sound and adiabatic index, respectively. The resulting data indicate that the compact stars in this modified framework are physically viable and stable.

gr-qc↗
arXiv2024

Viable and Stable Compact Stars in $f(\mathcal{Q})$ Theory

In this paper, we study the viability and stability of anisotropic compact stars in the context of $f(\mathcal{Q})$ theory, where $\mathcal{Q}$ is non-metricity scalar. We use Finch-Skea solutions to investigate the physical properties of compact stars. To determine the values of unknown constants, we match internal spacetime with the exterior region at the boundary surface. Furthermore, we study the various physical quantities, including effective matter variables, energy conditions and equation of state parameters inside the considered compact stars. The equilibrium and stability states of the proposed compact stars are examined through the Tolman-Oppenheimer-Volkoff equation, causality condition, Herrera cracking approach and adiabatic index, respectively. It is found that viable and stable compact stars exist in $f(\mathcal{Q})$ theory as all the necessary conditions are satisfied.

gr-qc↗
arXiv2020

Generalized Gravitational Baryogenesis of Well-Known $f(T,T_G)$ and $f(T,B)$ Models

The baryogenesis presents the theoretical mechanism that describes the matter-antimatter asymmetry in the history of early universe. In this work, we investigate the gravitational baryogenesis phenomena in the frameworks of $f(T, T_G)$ (where $T$ and $T_G$ are the torsion scalar and teleparallel equivalent to the Gauss-Bonnet term respectively) and $f(T, B)$ (where $B$ denotes the boundary term between torsion and Ricci scalar) gravities. For $f(T,T_G)$-gravity, we consider two generic power law models while logarithmic and general Taylor expansion models for $f(T,B)$-gravity. We consider power law scale factor for each model and compute baryon to entropy ratio by assuming that the universe filled by perfect fluid and dark energy. We find generalized baryogenesis interaction which is proportional to $\partial_μf(T+T_G)$ and $\partial_μf(T+B)$ for both theories of gravity. We compare our results against current astrophysical data of baryon to entropy ratio, which indicates excellent consistency with observational bounds (i.e., $\frac{η_B}{S} = 9.42 \times 10^{-11}$).

gr-qc↗
arXiv2019

Cosmological Consequences of New Dark Energy Models in Einstein-Aether Gravity

In this paper, we reconstruct various solutions for the accelerated universe in the Einstein-Aether theory of gravity. For this purpose, we obtain the effective density and pressure for Einstein-Aether theory. We reconstruct the Einstein-Aether models by comparing its energy density with various newly proposed holographic dark energy models such as Tsallis, R$\acute{e}$nyi and Sharma-Mittal. For this reconstruction, we use two forms of scale factor, power-law and exponential forms. The cosmological analysis of underlying scenario has been done by exploring different cosmological parameters. This includes equation of state parameter, squared speed of sound and evolutionary equation of state parameter via graphical representation. We obtain some favorable results for some values of model parameters.

physics.gen-ph↗
arXiv2018

Cosmological Implications of the Generalized Entropy Based Holographic Dark Energy Models in Dynamical Chern-Simons Modified Gravity

Recently, Tsallis, Rényi and Sharma-Mitall and entropies have widely been used to study the gravitational and cosmological setups. We consider a flat FRW universe with linear interaction between dark energy and dark matter. We discuss the dark energy models using Tsallis, Rényi and Sharma-Mitall entropies in the framework of Chern-Simons modified gravity. We explore various cosmological parameters (equation of state parameter, squared sound of speed ) and cosmological plane ($ω_{d}-ω_{d}'$, where $ω_{d}'$, is the evolutionary equation of state parameter). It is observed that the equation of state parameter gives quintessence-like nature of the universe in most of the cases. Also, the squared speed of sound shows stability of the models for Tsallis, Rényi dark energy model while unstable behavior for Sharma-Mitall dark energy model. The $ω_{d}-ω_{d}'$ plane represents the thawing region for all dark energy models.

physics.gen-ph↗
arXiv2018

Thermodynamics of Various Entropies in Specific Modified Gravity with Particle Creation

We consider the particle creation scenario in the dynamical Chern-Simons modified gravity in the presence of perfect fluid equation of state $p=(γ-1)ρ$. By assuming various modified entropies (Bekenstein, logarithmic, power law correction and Reyni), we investigate the first law of thermodynamics and generalized second law of thermodynamics on the apparent horizon. In the presence of particle creation rate, we discuss the generalized second law of thermodynamics and thermal equilibrium condition. It is found that thermodynamic laws and equilibrium condition remain valid under certain conditions of parameters.

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

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

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

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

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↗
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↗
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↗