Anisotropic Dark Energy Research Articles

Five dimensional anisotropic dark energy model in f(R,T) gravity

Five dimensional Kaluza-Klein space-time is considered in the presence of anisotropic dark energy in f(R,T) gravity proposed by Harko et al. (Phys. Rev. D 84:024020, 2011). To obtain a determinate solution of the field equations we have used the special law of variation for Hubble’s parameter given by Bermann (Nuovo Cimento B74:182, 1983). Some physical and kinematical properties of the model are also discussed.

Hypersurface-homogeneous space-time with anisotropic dark energy in scalar tensor theory of gravitation

The exact solutions of the field equations for Hypersurface-homogeneous space time under the assumption on the anisotropy of the fluid (dark energy) are obtained for exponential and power-law volumetric expansions in a scalar-tensor theory of gravitation proposed by Saez and Ballester (Phys. Lett. A 113:467, 1985). The physical and kinematical properties of the universe have been discussed.

Unified dark fluid in Brans–Dicke theory

Anisotropic dark energy cosmological models are constructed in the frame work of generalised Brans-Dicke theory with a self interacting potential. Wet dark fluid characterized by a linear equation of state is considered as the source of dark energy. Shear scalar is considered to be proportional to the expansion scalar simulating an anisotropic relationship among the directional expansion rates. The dynamics of the universe in presence of wet dark fluid in anisotropic background have been discussed. The presence of evolving scalar field makes it possible to get accelerating phase of expansion even for a linear relationship among the directional Hubble rates. It is found that, the anisotropy in expansion rates does not affect the scalar field, self interacting potential but it controls the non-evolving part of the Brans- Dicke parameter.

Evaluation of Bianchi type VI0 magnetized anisotropic dark energy models with constant deceleration parameter in bimetric theory of gravitation

In this paper, Bianchi type VI0 magnetized anisotropic dark energy models with constant deceleration parameter have been studied by solving the Rosen's field equations in Bimetric theory of gravitation. The models corresponding to power law expansion and exponential law expansion have been evaluated and studied their nature geometrically and physically. It is seen that there is real visible matter (baryonic matter) suddenly appeared only for small interval of time 0.7 ≤ t < 0.7598 and for the remaining whole range of time t, there is dark energy matter in the universe. Our investigations are supported to the observational fact that the usual matter described by known particle theory is about 4% and the dark energy cause the accelerating expansion of the universe and several high precision observational experiments, especially the Wilkinson Microwave Anisotropic Probe (WMAP) satellite experiment (see [C. L. Bennett et al., Astrophys. J. Suppl. Ser. 148 (2003) 1; WMAP Collab. (D. N. Spergel et al.), Astrophys. J. Suppl. Ser. 148 (2003) 175; D. N. Spergel et al., Astrophys. J. Suppl. 170 (2007) 377; WMAP Collab. (E. Komastu et al.), Astrophys. J. Suppl. 180 (2009) 330; WMAP Collab. (G. Hinshaw et al.), Astrophys. J. Suppl. 208 (2013) 19; Plank Collab. (P. A. R. Ade), arXiv:1303.5076; arXiv:1303.5082]) conclude that the dark energy occupies near about 73% of the energy of the universe and dark matter is about 23%. In exponential law of expansion, our model is fully occupied by real visible matter and there is no chance of dark energy and dark matter.

Hypersurface Homogeneous Space Time with Anisotropic Dark Energy in Brans Dicke Theory of Gravitation

The main purpose of the present paper is to explore hypersurface homogenous space time in Brans Dicke theory of gravitation in terms of the dark energy source. To obtain solution of the field equation, we have taken into account the relation between ϕ and the average scale factor a. The volumetric expansions are considered to get deterministic solutions. Physical properties of the models are also discussed in detail.

Axially symmetric cosmological model with anisotropic dark energy

The axially symmetric cosmological model is investigated in the presence of anisotropic dark energy. Exact solutions of the Einstein field equations are obtained by a special law of variation for the mean Hubble parameter, which yields a constant value of the deceleration parameter. Geometrical and kinematic properties of the model and the anisotropy of the dark energy have been carried out.

Kaluza Klein universe with magnetized anisotropic dark energy in general relativity and Lyra manifold

In this paper, the authors have investigated the Kaluza Klein universe with magnetized anisotropic dark energy in the context of Lyra manifold. Exponential and power law volumetric expansion is assumed to obtain the solution of the field equations. It is observed that magnetic field plays significant role in isotropization of the dark energy. The physical parameters of the models have been discussed in detail.

The traces of anisotropic dark energy in light of Planck

We study a dark energy model with non-zero anisotropic stress, either linked to the dark energy density or to the dark matter density. We compute approximate solutions that allow to characterise the behaviour of the dark energy model and to assess the stability of the perturbations. We also determine the current limits on such an anisotropic stress from the cosmic microwave background data by the Planck satellite, and derive the corresponding constraints on the modified growth parameters like the growth index, the effective Newton's constant and the gravitational slip.

Bianchi Type II, VIII & IX Cosmological Model with Magnetized Anisotropic Dark Energy in Brans-Dicke Theory of Gravitation

In the present paper we studied Bianchi type II, VIII & IX space time in the presence of magnetized anisotropic dark energy in Brans-Dicke theory of gravitation. The exact solution of the field equations under the assumption on the anisotropy of the fluid are obtained for exponential and power law expansions. The obtained models approach isotropy asymptotically at large value of t. Some physical properties of the model are discussed.

Magnetized anisotropic dark energy cosmological models in scale covariant theory of gravitation

In the present paper, we have investigated Bianchi type II, VIII and IX spacetime in the presence of magnetized anisotropic dark energy in the Scale covariant theory of gravitation. Exact solution of the field equations are obtained by assuming the expansion anisotropy (the ratio of shear scalar to expansion scalar) to be a function of average scale factor. The isotropy of the fluid, space and expansion are examined.

Exact Kantowski-Sachs Anisotropic Dark Energy Cosmological Models in Brans Dicke Theory of Gravitation

The main purpose of this paper is to explore the solution of Exact Kantowski-Sach cosmological models by using the Brans Dicke Theory of gravitation in the background of anisotropic dark energy. In order to obtain different physically variable models of the universe we have assumed the special law of variation of Hubbles parameter proposed by Berman (Nuovo Cimento B 74:182, 1983) which yields constant deceleration parameter and power law relation between average scale factor R and scalar field f, which has already been used by Johri and Desikan in RW Brans Dicke models. Some physical and geometrical consequences of the models have been carried out by using some physical quantities.

Strange star model with Tolmann IV type potential

We report a general solution in one of the gravitational potentials to the Einstein system in static spherically symmetric spacetime, modeling anisotropic strange quark matter by imposing a linear barotropic equation of state. The model generated by choosing Tolmann IV form for the gravitational potential is shown to contain the previously known anisotropic dark energy star model of Lobo (Class. Quantum Gravity 23:1525, 2006) and isotropic models of de Sitter and Einstein. Moreover, the model is shown to be physically admissible and corroborate with experimental observations on strange star candidates such as SAX J1808.4-3658 and 4U 1820-30.

Cosmic microwave background anomalies from imperfect dark energy

We test anisotropic dark energy models with the 7-year WMAP temperature observations data. In the presence of imperfect sources, due to large-scale gradients or anisotropies in the dark energy field, the CMB sky will be distorted anisotropically on its way to us by the ISW effect. The signal covariance matrix then becomes nondiagonal for small multipoles, but at $\ell \gtrsim 20$ the anisotropy is negligible. We parametrize possible violations of rotational invariance in the late universe by the magnitude of a post-Friedmannian deviation from isotropy and its scale dependence. This allows to obtain hints on possible imperfect nature of dark energy and the large-angle anomalous features in the CMB. A robust statistical analysis, subjected to various tests and consistency checks, is performed to compare the predicted correlations with those obtained from the satellite-measured CMB full sky maps. The preferred axis point towards $(l,b) = (168^\circ, -31^\circ)$ and the amplitude of the anisotropy is $\varpi_0 = (0.51\pm 0.94)$ (1$\sigma$ deviation quoted). The best-fit model has a steep blue anisotropic spectrum ($n_{\mathrm{de}} = 3.1\pm1.5$).

Isotropic and anisotropic dark energy models

In this review we discuss the evolution of the universe filled with dark energy with or without perfect fluid. In doing so we consider a number of cosmological models, namely Bianchi type I, III, V, VI0, VI and FRW ones. For the anisotropic cosmological models we have used proportionality condition as an additional constrain. The exact solutions to the field equations in quadrature are found in case of a BVI model. It was found that the proportionality condition used here imposed severe restriction on the energy-momentum tensor, namely it leads to isotropic distribution of matter.

Magnetized Anisotropic Dark Energy Models in Barber’s Second Self-Creation Theory

The present paper deals with Bianchi type IX cosmological model with magnetized anisotropic dark energy by using Barber’s self-creation theory. The energy momentum tensor consists of anisotropic fluid with EoS parameterωand a uniform magnetic field of energy densityρB. In order to obtain the exact solution we have assumed that dark energy components and the components of magnetic field interact minimally and obey the law of conservation of energy momentum tensors. We have also used the special law of variation for the mean generalized Hubble parameter and power law relation between scalar field and scale factor. Some physical and kinematical properties of the models have been discussed.

The Measurement of and in Bianchi Type-I Anisotropic Dark Energy Cosmological Model with Constant Deceleration Parameter in Bimetric Theory of Gravitation

The Measurement of and in Bianchi Type-I Anisotropic Dark Energy Cosmological Model with Constant Deceleration Parameter in Bimetric Theory of Gravitation

Anisotropic Dark Energy Bianchi Type-II Cosmological Models in Lyra Geometry

The spatially homogeneous and totally anisotropic Bianchi type-II cosmological model has been discussed in general relativity in the presence of a hypothetical anisotropic dark energy fluid with constant deceleration parameter within the frame work of Lyra’s manifold with uniform and time varying displacement field vector. With the help of special law of variation for Hubble’s parameter proposed by Bermann (Nuovo Cimento 74B:182, 1983) a dark energy cosmological model is obtained in this theory. We use the power law relation between average Hubble parameter H and average scale factor R to find the solution. The assumption of constant deceleration parameter leads to two models of universe, i.e. power law model and exponential model. Some physical and kinematical properties of the model are also discussed.

Constraining the anisotropic expansion of the Universe

We study the possibly existing anisotropy in the accelerating expansion universe with the Union2 Type Ia supernovae data and Gamma-ray burst data. We construct a direction-dependent dark energy model and constrain the anisotropy direction and strength of modulation. We find that the maximum anisotropic deviation direction is $(l,\,b)=(126^{\circ},\,13^{\circ})$ (or equivalently $(l,\,b)=(306^{\circ},\,-13^{\circ})$), and the current anisotropy level is $g_0=0.030_{+0.010}^{-0.030}$ ($1\sigma$ confidence level with Union2 data). Our results do not show strong evidence for the anisotropic dark energy model. We also discuss potential methods that may distinguish the peculiar velocity field from the anisotropic dark energy model.

LRS Bianchi Type-I Dark Energy Cosmological Models in General Scalar Tensor Theory of Gravitation

Locally rotationally symmetric (LRS) Bianchi type-I dark energy cosmological model with variable equation of state (EoS) parameter in (Nordtvedt 1970) general scalar tensor theory of gravitation with the help of a special case proposed by (Schwinger 1970) is obtained. It is observed that these anisotropic and isotropic dark energy cosmological models always represent an accelerated universe and are consistent with the recent observations of type-Ia supernovae. Some important features of the models, thus obtained, have been discussed.

Bianchi Type-III Cosmological Models with Anisotropic Dark Energy (DE) in Lyra Geometry

The main purpose of this paper is to explore the solutions of Bianchi type-III cosmological model in Lyra geometry in the background of anisotropic dark energy. The general form of the anisotropy parameter of the expansion for Bianchi type-III space time is obtained in the presence of a single imperfect fluid with a dynamical anisotropic equation of state parameter and a dynamical energy density in Lyra geometry. A special law is assumed for the anisotropy of the fluid with reduces the anisotropy parameter of the expansion to a simple form \(\Delta \propto \frac{1}{H^{2}V^{2}}\). The exact solutions of the field equations, under the assumption on the anisotropy of the fluid, are obtained for exponential and power law volumetric expansion. The isotropy of the fluid, space and expansion are discussed. It is observed that the universe can approach to isotropy monotonically even in the presence of an anisotropic fluid. The anisotropy of the fluid also isotropizes at later times for accelerating models. The expression for the look-back time, proper distance, luminosity distance and angular diameter distance are also derived.