Dynamics of Bianchi I universe with magnetized anisotropic Dark Energy

We study Bianchi type I cosmological model in the presence of magnetized anisotropic dark energy. The energy-momentum tensor consists of anisotropic fluid with anisotropic EoS p=ω ρ and a uniform magnetic field of energy density ρ _B . We obtain exact solutions to the field equations using the condition that expansion is proportional to the shear scalar. The physical behavior of the model is discussed with and without magnetic field. We conclude that universe model as well as anisotropic fluid do not approach isotropy through the evolution of the universe.     

Dynamics of a magnetized Bianchi VI 0 universe with anisotropic fluid

We discuss spatially homogeneous and anisotropic Bianchi type VI ₀ cosmological model with anisotropic fluid and magnetic field. The energy-momentum tensor consists of anisotropic fluid with anisotropic EoS and a uniform magnetic field of energy density ρ _B . Exact solution of the field equations is obtained by using the condition that expansion is proportional to the shear scalar. We focus on the future evolution of the model both in the presence and absence of magnetic field. In particular, we address the question whether these models approach to isotropy.     

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.     

Cosmic strings and viscous matter in a Kantowski-Sachs universe

We study the dynamics of a universe where the matter content is represented by a radially directed distribution of cosmic strings plus matter admitting both shear and bulk viscosity. We assume specific forms for the equation of state of both the strings and matter and discuss the cosmological solutions obtained.     

Thermodynamics in non-linear electrodynamics with anisotropic universe

In this work, we consider the framework of non-linear electrodynamics in Bianchi type I universe model composed of matter and electromagnetic field. We deal with electric and magnetic universe separately. In this scenario, we calculate the electric and magnetic fields and their corresponding matter densities using two particular types of interaction terms. We also check the validity of generalized second law of thermodynamics in both universe models enclosed by apparent horizon. It turns out that this law holds on the apparent horizon for a particular range depending upon the parameters. Finally, we discuss the deceleration and statefinder parameters to check the viability of these models.     

Dynamics of viscous universe

The dynamics of the viscous Robertson-Walker universe is presented using the phase variables method. Connection between violence of the strong energy condition and the behaviour of the Universe near the singularity is discussed.     

String cosmology with magnetized bulk viscous fluid in Bianchi I universe

The objective of the present paper is to study an anisotropic Bianchi-I cosmological model filled with bulk viscous fluid and magnetic field in string cosmology. The magnetic field is due to an electric current produced along the x-axis. The expansion in the model is considered to be proportional to one of the components of the shear tensor. We obtain two different quadrature forms of volume scale factor by considering two different relations between bulk viscosity and expansion scalar. We discuss the behavior of the classical potential with respect to the volume scale factor in the presence or absence of magnetic field and bulk viscosity in each case. We observe the role of bulk viscosity on the classical potential and also on the choices of bulk viscous pressure. By introduction of magnetic field or bulk viscosity or both into the model it results in changes in the potential as well as in volume scale factors. The physical and geometrical aspects of the solutions are discussed in detail.     

Thermodynamics and cosmic expansion in magnetized chameleonic Brans-Dicke universe

This study is emphasized to explore the validity of generalized second law of thermodynamics in the context of non-linear electrodynamics (magnetic effects only) with Brans-Dicke chameleon scalar field as dark energy candidate. For this purpose, we consider FRW universe model with perfect fluid matter contents. We evaluate matter energy density and magnetic field by taking interacting and non-interacting cases of magnetic field and matter as well as the power law ansatz for scalar field. The validity of this law is discussed by using the first law of thermodynamics for four different horizons: Hubble, apparent, particle and event horizons. We conclude that this law may hold for all four horizons with small positive red-shift when chameleon mechanism is taken into account in Brans-Dicke gravity. Finally, we investigate the statefinders in order to check the viability of the model.     

Interaction of Gravitational field and Brans-Dicke field in R/W universe containing Dark Energy like fluid

On studying some new models of Robertson-Walker universes with a Brans-Dicke scalar field, it is found that most of these universes contain a dark energy like fluid which confirms the present scenario of the expansion of the universe. In one of the cases, the exact solution of the field equations gives a universe with a false vacuum, while in another it reduces to that of dust distribution in the Brans-Dicke cosmology when the cosmological constant is not in the picture. In one particular model it is found that the universe may undergo a Big Rip in the future, and thus it will be very interesting to investigate such models further.     

Probing Dark Energy with Supernova Searches

Four years ago, two teams presented independent analyzes coming from photometry of type Ia supernovae at various distances. The results presented back then shook-up the scientific community: the universe is accelerating with a positive repulsive fluid sometimes called dark energy. No significant work has disproved the fundamental results, yet some doubt subsists in the assumptions behind the full use of type Ia supernovae as perfect distance indicators. The uncertainty of the evolution problem, the explosion mechanisms and the diversity of the observed light curves properties are often cited problems. All these aspects are now being deeply investigated in to-come or already started supernova searches along with the on-going quest of determining the nature of dark energy. We will present here a brief introduction to the use of type Ia supernova in cosmology, the current status of supernova cosmology as well as an overview of the wide supernova surveys about to begin.     

Holographic dark energy model with variable deceleration parameter,cosmic coincidence and the future singularity of the Kantowski-Sachs universe

The present work deals with a spatially homogeneous and anisotropic Kantowski-Sachs space time filled with two minimally interacting fluids; dark matter and a hypothetical anisotropic fluid as the holographic dark energy components. To obtain an exact solution of the Einstein’s field equations, we used the assumption of linearly varying deceleration parameter. We have investigated geometric and kinematic properties of the model and the role of the anisotropic holographic dark energy in the evolution of the Kantowski-Sachs universe. Under the suitable condition, it is observed that the anisotropy parameter of the universe and the skewness parameter of the holographic dark energy approaches to zero for large cosmic time and the universe can achieve flatness for some particular moments throughout its entire lifetime. Results show that the coincidence parameter $( \Re= \frac{\rho_{\varLambda}}{\rho_{M}} )$ increases with increasing time and a big rip type future singularity will occur for this model. We have also applied the statefinder diagnostics method to study the behavior of different stages of the universe and to differentiate the proposed dark energy model from the ΛCDM model. Since in this model, the universe has a finite life time and passes through a significant time when the dark energy and the matter energy densities are roughly comparable, so considering $\frac{1}{ \Re_{0}} <\Re < \Re_{0}$ , where ?₀ is any fixed ratio, we have calculated the fraction of total life time of the universe when the universe passes through the coincidental stage for this future singularity. The results are found to be consistent with recent cosmological observations.     

Effect of modified Chaplygin gas in anisotropic universe

In this work, we have studied the model of modified Chaplygin gas and its role in accelerating phase of the universe for anisotropic model. We have assumed that the equation of state of this modified model is valid from the radiation era to ΛCDM model. We have obtained the possible relation between the hessence and the modified Chaplygin gas. We have also use the statefinder parameters for characterize different phase of the universe diagrammatically.     

Energy distributions of Kantowski-Sachs space-time in the theory of teleparallel gravity

We calculate the energy density and energy distribution of Kantowski-Sachs space-time, using Einstein, Bergmann-Thomson and Landau-Lifshitz energy-momentum complexes, in the theory of teleparallel gravity. A comparison of the results shows that the Einstein and Bergmann-Thomson definitions furnish a consistent result for the energy density and energy distribution, but the definition of Landau-Lifshitz does not concur with them. We show that the space-time under consideration gives a counterexample that the energy distribution is the same either in general relativity or teleparallel gravity.     

Dark Energy in the Universe

I 24 Studying the Nature of Dark Energy with Galaxy Clusters I 50 Constraining Dark Energy via Baryon Acoustic Oscillations I 65 Constraining Dark Energy with Redshift Surveys I 103 Dark Energy: Necessity, Models and Expectations I 177 Searching for galaxy clusters through weak lensing, X‐rays and the SZ observations I 181 SNIa and Dark Energy     

Dark energy model in anisotropic Bianchi type-III space-time with variable EoS parameter

A new dark energy model in anisotropic Bianchi type-III space-time with variable equation of state (EoS) parameter has been investigated in the present paper. To get the deterministic model, we consider that the expansion θ in the model is proportional to the eigen value s² ₂\sigma^{2}_{~2} of the shear tensor s^j _i\sigma^{j}_{~i}. The EoS parameter ω is found to be time dependent and its existing range for this model is in good agreement with the recent observations of SNe Ia data (Knop et al. in Astrophys. J. 598:102, 2003) and SNe Ia data with CMBR anisotropy and galaxy clustering statistics (Tegmark et al. in Astrophys. J. 606:702, 2004). It has been suggested that the dark energy that explains the observed accelerating expansion of the universe may arise due to the contribution to the vacuum energy of the EoS in a time dependent background. Some physical aspects of dark energy model are also discussed.     

Dark energy and future singularity of the universe in Kaluza-Klein space time

The dark energy model with the equation of state \(p_{\mathit{DE}} = {-} \rho_{\mathit{DE}} - A\rho_{\mathit{DE}}^{\alpha} \) is studied in Kaluza-Klein space time. The model comprises and provides realization of several types of singularities in different parameter regimes. We discuss the finite-time singularities into four classes and explicitly present the models which give rise to these singularities by assuming the form of the equation of state of dark energy. Also, we discussed the models in terms of the cosmological redshift and some observational parameters.