Charged gravastars admitting conformal motion

In this paper, we study two different models of dark energy based on the Chaplygin gas equation of state. The first model is the variable modified Chaplygin gas, while the second one is the extended Chaplygin gas. Both models are considered in the framework of higher order $$f(R)$$
 modified gravity. We also consider the case of time-varying gravitational constant $$G$$
 and $$\Lambda $$
 for both models. We investigate some cosmological parameters such as the Hubble, the deceleration, and the equation of state parameters. Then we show that the model that we consider, the extended Chaplygin gas with time-dependent $$G$$
 and $$\Lambda $$
 , is consistent with the observational data. Finally we conclude with the discussion of cosmological perturbations of our model.

https://link.springer.com/content/pdf/10.1140%2Fepjc%2Fs10052-015-3263-6.pdf

Higher order corrections of the extended Chaplygin gas cosmology with varying G and \Lambda

We propose extended Chaplygin gas equation of state for which it recovers barotropic fluid with quadratic equation of state. We use numerical method to investigate the behavior of some cosmological parameters such as scale factor, Hubble expansion parameter, energy density, and deceleration parameter. We also discuss the resulting effective equation of state parameter. Using density perturbations we investigate the stability of the theory.

/pdf/frw-cosmology-with-the-extended-chaplygin-gas-1ubcar1z26.pdf

FRW Cosmology with the Extended Chaplygin Gas

We propose a model for relativistic compact star with anisotropy and analytically obtain exact spherically symmetric solutions which describe interior of the dense star admitting non-static conformal symmetry. Several features of the solutions, including drawbacks of the model, have been explored and discussed. For this purpose we have provided the energy conditions, TOV equation and other physical requirements and thus thoroughly have investigated stability, mass-radius relation and surface redshift of the model. It is observed that most of the features are well matched with the compact strange stars.

Anisotropic stars with non-static conformal symmetry

A simple classification is given of the anisotropic relativistic star models, resembling the one of charged isotropic solutions. On the ground of this database, and taking into account the conditions for physically realistic star models, a method is proposed for generating all such solutions. It is based on the energy density and the radial pressure as seeding functions. Numerous relations between the realistic conditions are found and the need for a graphic proof is reduced just to one pair of inequalities. This general formalism is illustrated with an example of a class of solutions with linear equation of state and simple energy density. It is found that the solutions depend on three free constants and concrete examples are given. Some other popular models are studied with the same method.

/pdf/analytical-study-of-anisotropic-compact-star-models-4fmqxuu4m4.pdf

Analytical study of anisotropic compact star models

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) $p_{t}-p_{r}=\frac{1}{8\pi}(\frac{c_{1}}{r^{2}}+c_{2})$
 
where, n, c
 1 and c
 2 are arbitrary constants. The solutions yield expressions of the physical quantities like pressure gradients and the mass.

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

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

Motivated by earlier studies (Tiwari et al. in Astrophys. Space Sci. 182:105, 1984; Herrera and Varela in Phys. Lett. 189:11, 1994), we model electron as a spherically symmetric charged perfect fluid distribution of matter. The existing model is extended assuming a matter source that is characterized by quadratic equation of state in the context of general theory of relativity. For the suitable choices of the parameters, our charged fluid models almost satisfy the physical properties of electron.

Revisiting the classical electron model in general relativity

Lorentz proposed a classical model of electron in which electron was assumed to have only 'electromagnetic mass'. We modeled electron as charged anisotropic perfect fluid sphere admitting non static conformal symmetry. It is noticed that the pressure and density fail to be regular at the origin but effective gravitational mass is regular everywhere and vanishes at the limit r->0 i.e. it does not have to tolerate the problem of singularity. Further, we have matched interior metric with exterior (Reissner-Nordstrom) metric and determine the values of the parameters k and r_0 (occurring in the solutions) in functions of mass, charge and radius of the spherically symmetric charged objects i.e. electron.

Classical electron model with non static conformal symmetry

Electron is modeled as a spherically symmetric charged perfect fluid distribution of matter. The existing model is extended assuming a matter source that is characterized by quadratic EoS in the context of general theory of relativity. For the suitable choices of the parameters, our charged fluid models almost satisfy the physical properties of electron.

Kaushik Chakraborty

Papers

On role of pressure anisotropy for relativistic stars admitting conformal motion

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

Revisiting the classical electron model in general relativity

Classical electron model with non static conformal symmetry

Revisiting the classical electron model in general relativity