Abstract:
In this article we compute the density of scalar and Dirac particles created by a cosmological anisotropic Bianchi type I universe in the presence of a time varying electric field. We show that the particle distribution becomes thermal when one neglects the electric interaction.

Abstract:
Using squeezed vacuum state formalism of quantum optics, an approximate solution to the semiclassical Einstein equation is obtained in Bianchi type-I universe. The phenomena of nonclassical particle creation is also examined in the anisotropic background cosmology.

Abstract:
I study the dynamical effects due to the Brans-Dicke scalar $\phi$-field at the early stages of a supposedly anisotropic Universe expansion in the scalar-tensor cosmology of Jordan-Brans-Dicke. This is done considering the behaviour of the general solutions for the homogeneous model of Bianchi type VII in the vacuum case. I conclude that the Bianchi-VII$_0$ model shows an isotropic expansion and that its only physical solution is equivalent to a Friedman-Robertson-Walker spacetime whose evolution can, depending on the value of the JBD coupling constant, begin in a singularity and, after expanding (inflating, if $\omega>0$), shrink to another, or starting in a non-singular state, collapse to a singularity. I also conclude that the general Bianchi-VII$_h$ (with $h\neq 0$) models show strong curvature singularities producing a complete collapse of the homogeinity surfaces to 2D-manifolds, to 1D-manifolds or to single points. Our analysis depends crucially on the introduction of the so-called intrinsic time, $\Phi$, as the product of the JBD scalar field $\phi$ times a mean scale factor $a^3=a_1a_2a_3$, in which the finite-cosmological-time evolution of this universe unfolds into an infinite $\Phi$-range. These universes isotropize from an anisotropic initial state, thence I conclude that they are stable against anisotropic perturbations.

Abstract:
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 $p=\omega{\rho}$ and a uniform magnetic field of energy density $\rho_B$. 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.

Abstract:
An anisotropic Bianchi type-III cosmological model is investigated in the presence of a bulk viscous fluid within the framework of Lyra geometry with time-dependent displacement vector. It is shown that the field equations are solvable for any arbitrary function of a scale factor. To get the deterministic model of the universe, we have assumed that (i) a simple power-law form of a scale factor and (ii) the bulk viscosity coefficient are proportional to the energy density of the matter. The exact solutions of the Einstein’s field equations are obtained which represent an expanding, shearing, and decelerating model of the universe. Some physical and kinematical behaviors of the cosmological model are briefly discussed. 1. Introduction After Einstein (1916) proposed his theory of general relativity which provided a geometrical description of gravitation, many physicists attempted to generalize the idea of geometrizing the gravitation to include a geometrical description of electromagnetism. One of the first attempts was made by Weyl [1] who proposed a more general theory by formulating a new kind of gauge theory involving metric tensor to geometrize gravitation and electromagnetism. But Weyl theory was criticized due to the nonintegrability of length of vector under parallel displacement. Later, Lyra [2] suggested a modification of Riemannian geometry by introducing a gauge function into the structureless manifold which removed the nonintegrability condition. This modified geometry is known as Lyra geometry. Subsequently, Sen [3] formulated a new scalar-tensor theory of gravitation and constructed an analogue of the Einstein’s field equations based on Lyra geometry. He investigated that the static model with finite density in Lyra manifold is similar to the static model in Einstein’s general relativity. Halford [4] has shown that the constant displacement vector field in Lyra geometry plays the role of cosmological constant in general relativity. He has also shown that the scalar-tensor treatment based in Lyra geometry predicts the same effects, within observational limits, as in Einstein’s theory (Halford, [5]). Soleng [6] has investigated cosmological models based on Lyra geometry and has shown that the constant gauge vector field either includes a creation field and be identical to Hoyle’s creation cosmology (Hoyle, [7], Hoyle, and Narlikar [8, 9]) or contains a special vacuum field which together with the gauge vector term may be considered as a cosmological term. In the latter case, solutions are identical to the general relativistic cosmologies with

Abstract:
Spatially homogeneous and anisotropic Bianchi type $VI_0$ cosmological models with cosmological constant are investigated in the presence of anisotropic dark energy. We examine the effects of electromagnetic field on the dynamics of the universe and anisotropic behavior of dark energy. The law of variation of the mean Hubble parameter is used to find exact solutions of the Einstein field equations. We find that electromagnetic field promotes anisotropic behavior of dark energy which becomes isotropic for future evolution. It is concluded that the isotropic behavior of the universe model is seen even in the presence of electromagnetic field and anisotropic fluid.

Abstract:
A spatially homogeneous and anisotropic Bianchi Type I universe has been studied with {\omega} <-1 without Big Smash. It is demonstrated that if cosmic dark energy behaves like a fluid with equation of state p = {\omega}{\rho} (p and {\rho} being pressure and energy density respectively) as well as generalized chaplygin gas simultaneously, Big Rip or Big Smash problem does not arise even for equation of state parameter {\omega} <-1 unlike other phantom models, here, the scale factor for Bianchi Type I universe is found regular for all time. The present model is derived by using law of variation of Hubble's parameter from Bianchi Type I space-time and also the effective role of GCG behaviour is discussed.

Abstract:
In the present article we analyze the phenomenon of particle creation in a cosmological anisotropic universe when a constant electric field is present. We compute, via the Bogoliubov transformations, the density number of particles created.

Abstract:
Self-consistent system of nonlinear spinor field and Bianchi I (BI) gravitational one with time dependent gravitational constant ($G$) and cosmological constant ($\Lambda$) has been studied. The initial and the asymptotic behaviors of the field functions and the metric one have been thoroughly investigated. Given $\Lambda = \Lambda_0/\tau^2$, with $\tau = \sqrt{-g}$, $G$ has been estimated as a function of $\tau$. The role of perfect fluid at the initial state of expansion and asymptotical isotropization process of the initailly anisotropic universe has been elucidated.

Abstract:
We have studied the Hoyle-Narlikar C-field cosmology with Bianchi type-V non static space- time in higher dimensions. Using methods of Narlikar and Padmanabham [1], the solutions have been studied when the creation field C is a function of time t only as space time is non static. The geometrical and physical aspects for model are also studied.