Two-Fluid Cosmological Models in Bianchi Type-V Space-Time

We have presented anisotropic, homogeneous two-fluid cosmological models using Bianchi type-V space-time. Here one fluid represents the matter content of the universe and another fluid is chosen to model the CMB radiation. The radiation and matter content of the universe are in interactive phase. Also we have discussed the behavior of fluid parameters and kinematical parameters.     

Implications of Time Varying Cosmological Constant on Kaluza-Klein Cosmological Model

In this paper, the cosmological model with variable $\varLambda= \alpha \frac{\dot{R}^{2}}{R^{2}} + \beta\frac{1}{R^{2}}$ in Kaluza-Klein metric have been studied. Here α and β are dimensionless parameters. The solutions to Einstein field equations which assume that the Universe is filled with perfect fluid have been obtained by using the Gamma Law Equation p=(γ?1)ρ; in which the parameter γ is constant and power law equation A(t)=R ⁿ (t)—where A(t) is scale factor for extra dimension and R(t) is scale factor for space dimensions. The fifth dimension for the radiation dominated phases is more prominent with this model. Other physical parameters i.e. density, pressure, deceleration parameter, Hubble parameter have been determined for this model. It is observed physical parameters depends upon constants α, β and n. Neo-classical tests have also been studied in this paper.     

Kasner Cosmological Models with Two-Fluid Source in General Relativity

In this paper we present Bianchi type-I metric of the Kasner form describing two-fluid source of the universe in general relativity. In Kasner cosmological models one fluid is a radiation field modeling the cosmic microwave background, while the other is a matter field, modeling material content of the universe. The radiation and matter content of the universe are in interactive phase. We have also presented anisotropic, homogeneous nature of Kasner cosmological models with two-fluid. The behavior of fluid parameters and kinematical parameters of the models are also discussed.     

Cosmological Two-Fluid Thermodynamics

We reveal unifying thermodynamic aspects of so different phenomena as the cosmological electron-positron annihilation, the evaporation of primordial black holes with a narrow mass range, and the "deflationary" transition from an initial de Sitter phase to a subsequent standard Friedmann–Lemaître–Robertson–Walker (FLRW) behavior.     

Cosmological Kaluza-Klein monopoles

A solution of a pair of monopoles in 5D Kaluza-Klein theory without matter fields is given. The scale of the internal space is the same as that of the outer space. Its euclidean version is useful for calculating the wave function of the universe with monopoles.     

Higher Dimensional Plane Symmetric Cosmological Models with Two-Fluid Source in General Relativity

We consider anisotropic, homogeneous two-fluid plane symmetric cosmological models in higher dimensions. Here one fluid represents the matter content of the universe and another fluid is chosen to model the CMB (cosmic microwave background) radiation. The radiation and matter content of the universe are in interactive phase. Also we have discussed the behaviour of fluid parameters and kinematical parameters.     

Cosmological applications in Kaluza-Klein theory

The field equations of Kaluza–Klein (KK) theory have been applied in the domain of cosmology. These equations are solved for a flat universe by taking the gravitational and the cosmological constants as a function of time t. We use Taylor’s expansion of cosmological function, Λ(t), up to the first order of the time t. The cosmological parameters are calculated and some cosmological problems are discussed.     

Cosmological production of Kaluza-Klein monopoles

The cosmological production of Kaluza-Klein monopoles is discussed. The present monopole-to-entropy ratio is calculated in some simple models with the conclusion that this ratio is unacceptably large unless additional mechanisms for entropy production or monopole annihilation are present.     

Kaluza-Klein Cosmological Model in Self-Creation Cosmology

A five dimensional Kaluza-Klein Space-time is considered in the presence of a perfect fluid source in Barber’s (Gen. Relativ. Gravit. 14:117, 1982) second self-creation theory of gravitation. An exact cosmological model is presented using a relation between the metric potentials and an equation of state. Some physical and kinematical properties of the model are also discussed.     

Holographic Dark Energy (DE) Cosmological Models with Quintessence in Bianchi Type-V Space Time

In this paper, author studied homogeneous and anisotropic Bianchi type-V universe filled with matter and holographic dark energy (DE) components. The exact solutions to the corresponding Einstein’s field equations are obtained for exponential and power-law volumetric expansion. The holographic dark energy (DE) EoS parameter behaves like constant, i.e. ω _Λ =?1, which is mathematically equivalent to cosmological constant (Λ) for exponential expansion of the model, whereas the holographic dark energy (DE) EoS parameter behaves like quintessence for power-law expansion of the model. A correspondence between the holographic dark energy (DE) models with the quintessence dark energy (DE) is also established. Quintessence potential and dynamics of the quintessence scalar field are reconstructed, which describe accelerated expansion of the universe. The statefinder diagnostic pair {r,s} is adopted to characterize different phases of the universe.     

Cosmological compactification in Kaluza-Klein model and time-dependent cosmological term

Einstein's equations for the generalized (4+D)-dimensional Robertson-Walker model are solved taking the conformally invariant action for the matter field. Compactification of this model is discussed and the compactification time/compactification mass scale for different values ofD is calculated. The resulting 4-dimensional action for gravity is obtained. It is found that a time-dependent cosmological constant is induced which is very large when the cosmic time is small and very small when the cosmic time is large.     

Cosmological models in a Kaluza-Klein theory with variable rest mass

A general class of solutions is obtained for a homogeneous, spatially isotropic five-dimensional (5D) Kaluza-Klein theory with variable rest mass. These solutions generalize in the algebraic and physical sense the previously found solutions in the literature. The 4D spacetime sections of the solutions reduce to the Minkowski metric, K=0 Robertson-Walker metric with the equation of statep=np (p=pressure,n=constant sound speed,=energy density), and to the Robertson-Walker spacetime with steady-state metric. Some of the solutions, in different limits, show compactification of the fifth dimension. Some extensions of the model are discussed.     

Cosmological Models with Time Dependent G and A Coupling Scalars

A cosmologicM model in which the universe has its critical density and gravitational constants generalized as coupling scalars in Einstein＇s theory is considered. A general method of solving the field equations is given. An exact solution for matter distribution in cosmological models satisfying G = G0（ R/ R0）^n is presented. Corresponding physical interpretations of the cosmological solutions are also discussed.     

Bianchi Type-Ⅲ String Cosmological Models with Time Dependent Bulk Viscosity

Bianchi type-Ⅲ string cosmological models with bulk viscous fluid for massive string are investigated. To obtain the determinate model of the universe, we assume that the coeffcient of bulk viscosity ξ is inversely proportional to the expansion θ in the model and expansion θ in the model is proportional to the shear g. This leads to B =lC^n, where l and n are constants. Behaviour of the model in the presence and absence of bulk viscosity is discussed. The physical implications of the models are also discussed in detail.     

Two-Fluid Cosmological Model of Bianchi Type-V with Negative Constant Deceleration Parameter

This paper deals with a two-fluid Bianchi type-V anisotropic cosmological model with negative constant deceleration parameter. Exact solution of Einstein’s field equations for interacting matter and radiation field is presented which represents an expanding shearing and nonrotating cosmological model of the universe. This model describes the accelerated phase of the expanding universe. The physical and kinematical behaviors of the model are discussed.     

Asymptotic Symmetries in Cosmological Models

In the present article we study asymptotic isometries and asymptotic conformal Killing motions of some anisotropic Bianchi cosmological models. We show that asymptotically isotropic homogeneous cosmological spaces can be covariantly studied and characterized using scalars constructed with the help the Killing equations. We exhibit some illustrative examples of space-times possessing asymptotic Killing collineations. We apply our results in order to discuss asymptotic symmetries associated with scalar cosmological perturbations.     

Cosmological Constant and Stability of the Cosmological Models

The importance of cosmological constant for the cosmological models is given. The variations of the cosmological model for parameters λ and k were discussed respectively. Near λ = 0, the cosmological model is unstable with the change of λ, and near λ = β = 0, the cosmological model is unstable with the change of k. So when we consider the stable cosmological model, we must consider the nonzero cosmological constant.     

An Interacting and Non-interacting Two-Fluid Dark Energy Models in FRW Universe with Time Dependent Deceleration Parameter

We study the evolution of the dark energy parameter in a spatially homogeneous and isotropic FRW space-time filled with barotropic fluid and dark energy by considering a time dependent deceleration parameter. Two cases are discussed when the dark energy is minimally coupled to the perfect fluid as well as direct interaction with it. It is concluded that in both non-interacting and interacting cases only open and flat universes cross the phantom region. We find that during the evolution of the universe, the equation of state (EoS) for dark energy ω _D changes from ω _D >−1 to ω _D <−1, which is consistent with recent observations. The cosmic jerk parameter in our derived models is also found to be in good agreement with the recent data of astrophysical observations.