FRW Cosmological Models with Bulk-Viscosity in?Barber’s Second Self-Creation Theory

We have studied the evolution of spatially homogeneous and isotropic FRW cosmological model with bulk-viscosity in the frame work of Barber’s (Gen. Relativ. Gravit. 14: 117, 1982) second self-creation theory of gravitation. The cosmological models are obtained with the help of special law of variation for Hubble parameter proposed by Bermann (Nuovo Cimento 74B: 182, 1983). Physical parameters of the models have been discussed in case of false vacuum model, Zel’dovich fluid and radiation dominated fluid.     

On Kantowski-Sachs Cosmic Strings Coupled with Maxwell Fields in Bimetric Relativity

Kantowski-Sachs model is studied with source cosmic cloud strings coupled with electromagnetic field in Rosen’s (Gen. Relativ. Gravit. 4:435, 1973) bimetric theory of relativity. It is shown that there is no contribution from Maxwell fields in this theory. Hence geometric string and vacuum cosmological models are established.     

Axially Symmetric Cosmological Micro Model in Barber’s Modified Theory of Einstein General Relativity

Axially symmetric Bianchi type-I cosmological micro model is obtained in Barber’s (Gen. Relativ. Gravit. 14:117, 1982) modified theory of general relativity. Some properties of the model are discussed.     

String Cosmological Solutions in Self-Creation Theory of Gravitation

We have studied the problem of cosmic strings for Bianchi-I, II, VIII and IX string cosmological models in Barber’s (Gen. Relativ. Gravit. 14:117, 1982) second self—creation theory of gravitation. We have obtained some classes of solutions by considering different functional form for metric potentials. It is also observed that due to the presence of scalar field, the power index ‘m’ of the metric coefficients has a range of values.     

FRW Cosmological Solution in Self Creation Theory

In this paper, we have investigated spatially homogeneous isotropic Friedman-Robertson-Walker cosmological model with bulk viscosity and zero-mass scalar field in the frame work of Barber’s second self-creation theory (Gen. Relativ. Gravit. 14:117, 1982). The cosmological models are obtained with the help of the special law of variation for Hubble’s parameter proposed by Bermann (Nuovo Cimento B 74:182, 1983) and power law relation. Some physical properties of the models are also discussed.     

String Cloud with Quark Matter in Self-creation Cosmology

We have constructed Bianchi type-III cosmological model with strange quark matter attached to the string cloud in Barber’s (Gen. Relativ. Gravit. 14:117, 1982) second self-creation theory of gravitation which is inflationary. Further it is obtained that the theory leads to Einstein theory at initial epoch and at infinite future.     

Spherically Symmetric Cosmic Strings in Bimetric Theory

Spherically symmetric space-time is considered in bimetric theory of gravitation formulated by Rosen (Gen. Relativ. Gravit. 4:435, [1973]) in the presence of perfect fluid, massive scalar field and cosmic string. It is shown that either macro cosmological model represented by perfect fluid or cosmic string do not exist and only a vacuum model can be constructed whereas in case of a micro cosmological model represented by a scalar field exists and the model is obtained.     

Bianchi Types V and VI<Subscript>0</Subscript> Cosmic Strings Coupled with Maxwell Fields in Bimetric Theory

Spatially homogeneous Bianchi types V and VI₀ cosmological models are studied with source cosmic cloud strings coupled with electromagnetic field in Rosen’s (Gen. Relativ. Gravit. 4:435, 1973) bimetric theory of relativity. It is observed that Bianchi type V space time is feasible whereas Bianchi type VI₀ is not feasible. In the feasible case different equations of state for cosmic strings with Maxwell fields do not survive in this theory and the space-time turns out to be flat.     

Strange Quark Matter Attached to String Cosmology in FRW Space-Time

We have obtained FRW cosmological model with strange quark matter attached to the string cloud in general relativity. The model is obtained with the help of special law of variation for Hubble parameter proposed by Bermann (Nuovo Cimento 74B:182, 1983). Also, some physical and kinematics properties of the model are discussed. The results are analogous to results obtained by Yilmaz (Gen. Relativ. Gravit. 38:1397–1406, 2006).     

Axially Symmetric Cosmological Model with Wet Dark Fluid in Bimetric Theory of Gravitation

The purpose of this paper is to investigate the role of wet dark fluid in axially symmetric cosmological model within the frame work of bimetric theory of gravitation proposed by Rosen (Gen. Relativ. Gravit. 4:435, 1973). In this theory, it is observed that there is no contribution from wet dark fluid.     

Axially Symmetric Bianchi Type-I Model with Massless Scalar Field and Cosmic Strings in Barber’s Self-Creation Cosmology

Axially symmetric Bianchi type-I space time is considered in the presence of massless scalar field and cosmic strings in Barber’s (Gen. Relativ. Gravit. 14:117, 1982) self-creation theory with two conditions (i) A=B ⁿ and (ii) ε+λ=0. Some physical and kinematical properties of the model, thus obtained, are also discussed.     

On Axially Symmetric Domain Walls and Cosmic Strings in Bimetric Theory

It is shown that the axially symmetric thick domain walls and cosmic strings do not survive in the frame work of bimetric theory of gravitation proposed by Rosen (Gen. Relativ. Gravit. 4:435, 1973). Hence vacuum models are presented and studied.     

Inhomogeneous Plane Symmetric String Cosmological Models in Bimetric Theory

It is shown that the inhomogeneous plane symmetric perfect fluid distribution and cosmic strings do not survive in frame work of bimetric theory of gravitation proposed by Rosen (Gen. Relativ. Gravit. 4:435, 1973). Hence vacuum models are presented and studied.     

Note on “Continuous matter creation and the acceleration of the universe: the growth of density fluctuations”

Recently, de Roany and Pacheco (Gen Relativ Gravit, doi:) performed a Newtonian analysis on the evolution of perturbations for a class of relativistic cosmological models with Creation of Cold Dark Matter (CCDM) proposed by the present authors (Lima et al. in JCAP 1011:027, 2010). In this note we demonstrate that the basic equations adopted in their work do not recover the specific (unperturbed) CCDM model. Unlike to what happens in the original CCDM cosmology, their basic conclusions refer to a decelerating cosmological model in which there is no transition from a decelerating to an accelerating regime as required by SNe type Ia and complementary observations.     

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.     

Magnetized Bianchi Type III String Universe with Time Decaying Vacuum Energy Density Λ

Exact solution of Einstein’s field equations is obtained for massive string cosmological model of Bianchi III space-time using the technique given by Letelier (Phys. Rev. D 28:2414, 1983) in presence of perfect fluid and decaying vacuum energy density Λ. To get the deterministic solution of the field equations the expansion θ in the model is considered as proportional to the eigen value s² ₂\sigma^{2}_{~2} of the shear tensor s^j _i\sigma^{j}_{~i} and also the fluid obeys the barotropic equation of state. It is observed that the particle density and the tension density of the string are comparable at the two ends and they fall off asymptotically at similar rate. But in early stage as well as at the late time of the evolution of the universe we have two types of scenario (i) universe is dominated by massive strings and (ii) universe is dominated by strings depending on the nature of the two constants L and ℓ. The value of cosmological constant Λ for the model is found to be small and positive which is supported by the results from recent supernovae Ia observations. Some physical and geometric properties of the model are also discussed.     

Relaxation of vacuum energy in <Emphasis Type="Italic">q</Emphasis>-theory

The q-theory formalism aims to describe the thermodynamics and dynamics of the deep quantum vacuum. The thermodynamics leads to an exact cancellation of the quantum-field zero-point-energies in equilibrium, which partly solves the main cosmological constant problem. But, with reversible dynamics, the spatially flat Friedmann–Robertson–Walker universe asymptotically approaches the Minkowski vacuum only if the Big Bang already started out in an initial equilibrium state. Here, we extend q-theory by introducing dissipation from irreversible processes. Neglecting the possible instability of a de-Sitter vacuum, we obtain different scenarios with either a de-Sitter asymptote or collapse to a final singularity. The Minkowski asymptote still requires fine-tuning of the initial conditions. This suggests that, within the q-theory approach, the decay of the de-Sitter vacuum is a necessary condition for the dynamical solution of the cosmological constant problem.     

Cylindrically Symmetric Scalar Field and it’s Lyapunov stability in General Relativity

In this paper we found an Exact solution for massless scalar field with cosmological constant. This exact solution generalized the Levi-Civita vacuum solution Levi-Civita (Rend. Acc. Lincei 27:183, 1917) to a massless scalar field, with a cosmological constant term.This solution in the absence of the Cosmological constant recovers the spacetime of a massless scalar field with cylindrical symmetry (Buchdahl metric (Buchdahl in Phys. Rev. 115:1325, 1959)). Also if the scalar field disappears, the spacetime will be a representation of de-Sitter space.We prove that the form of the metric’s function which was purposed in Momeni and Miraghaei (Int. J. Mod. Phys. A 24(31):5991, 2009) is valid even if we assume a general form. Furthermore we show that in which conditions this solution satisfies energy conditions. Finally the credibility of focusing theorem is proved.     

The Cosmological constant and the coincidence problem in a new cosmological interpretation of the universal constant “c”

In a recent paper (Vigoureux et al. in Int. J. Theor. Phys. 47:928, 2007) it has been suggested that the velocity of light and the expansion of the universe are two aspects of one single concept connecting space and time in the expanding universe. It has then be shown that solving Friedmann’s equations with that interpretation (and keeping c=constant) can explain number of unnatural features of the standard cosmology (for example: the flatness problem, the problem of the observed uniformity in term of temperature and density of the cosmological background radiation, the small-scale inhomogeneity problem…) and leads to reconsider the Hubble diagram of distance moduli and redshifts as obtained from recent observations of type Ia supernovae without having to need an accelerating universe. In the present work we examine the problem of the cosmological constant. We show that our model can exactly generate Λ (equation of state P _φ =−ρ _φ c ² with Λ∝ R ⁻²) contrarily to the standard model which cannot generate it exactly. We also show how it can solve the so-called cosmic coincidence problem.