Rotating charged perfect-fluid universes coupled with scalar field in general relativity

Certain new analytic solutions for slowly-rotating charged perfect-fluid universes coupled with zero-mass scalar field are found out to substantiate the possibility of the existence of rotating cosmological objects of such nature and their dynamics is investigated. The nature and role of the metric rotation (r, t) as well as that of the matter rotation (r, t) under different conditions are studied. The effects of the charged field and the scalar field on the rotational motion are also discussed. In some solutions we find out the temporal restrictions on the models for real astrophysical situations. Rotating models which are expanding as well are obtained, in which cases the rotational velocities are found to decay with the time, and these models may be taken as good examples of real astrophysical objects in this Universe.     

Radiating anisotropic two-fluid model universes involving rotation in general relativity

Radiating anisotropic two-fluid model universes coupled with a scalar field when a slow rotation is introduced in them are studied here, where the anisotropic pressure is generated by the presence of two non-interacting perfect fluids which are in relative motion with respect to each other. Special discussion is made of the physically interesting class of models in which one fluid is a comoving radiative perfect fluid which is taken to model the cosmic microwave background and the second a non-comoving perfect fluid which will model the observed material content of the Universe. Here we take up four analytic solutions. The effects of rotation on these models are studied and the reactions of the scalar and the radiation fields with respect to the rotational motion are discussed. Analysis on the rotational perturbations are also made, in the course of which the amount of anisotropy induced in the pressure distribution by a small deviation from the Friedmann metric is also investigated. It is shown that such anisotropies could grow faster than the expansion of the Universe. The rotating models we obtain here are found to be theoretically satisfactory and they may be taken as physically acceptable models.     

Slowly rotating perfect-fluid universes coupled with zero-mass scalar field

Certain new analytic solutions for rotating perfect-fluid spheres in the Robertson-Walker universe are found out to substantiate the possibility of the existence of rotating cosmological objects coupled with zero-mass scalar field. Exact solutions for the metric rotation (r, t) and the matter rotation (r, t) under different conditions are obtained and their nature and role are investigated. Except for perfect dragging the scalar field is found to have a damping effect on the rotation of matter. In some solutions we find out the restrictions on the radii of the models for realistic astrophysical situations. Rotating models which can also be expanding are also obtained, in which case the rotational velocities are found to decay with the time; and these models may be taken as examples of real astrophysical objects in the Universe.     

Rotational perturbations of magneto-viscous fluid universes coupled with zero-mass scalar field

The dynamics of slowly rotating magneto-viscous fluid universe coupled with zero-mass scalar field is investigated, and the rotational perturbations of such models are studied in order to substantiate the possibility that the Universe is endowed with slow rotation, in the course of presentation of several new analytic solutions. Four different cases are taken up in which the nature and role of the metric rotation (r, t) as well as that of the matter rotation(r,t) are discussed. Except for the case of perfect drag, the scalar field is found to have a damping effect on the rotational motion. This damping effect is seen to be roughly analogous to the viscosity. The periods of physical validity of some of the models are also found out. Most of the rotating models obtained here come out to be expanding ones as well which may be taken as good examples of real astrophysical situations.     

Some rotating perfect fluid universes coupled with electromagnetic field interacting with gravitation

Some new interesting solutions, the dynamics, behaviour and phenomena of rotating charged perfect fluid models are investigated, and their physical and geometrical properties are studied in order to substantiate the possibility of the existence of such astrophysical bodies in this Universe. The nature and role of the metric rotation Ω(r,t) as well as that of the matter rotation ω(r,t) are studied for uniform and non-uniform motions. The reactions of the gravitational and charged fields with respect to the rotational motion are studied and possible results are explored for real astrophysical situations, and in some solutions we find the spatial restrictions on the models for realistic conditions. Rotating models which are expanding are obtained in which the rotational motions are decaying with time.     

Rotational perturbations of radiating Universes coupled with zero-mass scalar field

Investigations are made on slowly rotating radiating Universes coupled with a scalar field in the spherically symmetric Einstein formalism, and some new interesting solutions are obtained. Their physical and geometrical properties are studied from various angles. The rotational perturbations of such models are examined in order to substantiate the possibility that the universe is endowed with some rotation. The nature and role of the metric rotation as well as that of the rotation of matter are studied, and the effects of radiation and scalar fields on them are discussed. The models here turn out to be rotating as well as expanding ones, which may be taken as good examples of real astrophysical objects in this universe. The periods of the physical validity and the restrictions on the radii of the models for real astrophysical situations are obtained and discussed. The models obtained here are theoretically satisfactory and therefore there is a possibility that there may be less known objects in this universe which may be represented by our model Universes obtained here and many unknown properties of this universe may be explored and unfolded in the study of these models.     

Rotational perturbations of relativistic perfect-fluid model universes interacting with gravitational field

Along with the presentation of several new analytic solutions, the dynamics of slowly rotating perfect-fluid model universes are investigated, and their physical and geometrical properties are discussed from all angles. The rotational perturbations of such models are examined in detail in order to substantiate the possibility that the Universe is endowed with some rotation. The nature and role of the rotational velocity (r, t) which is related to the local dragging of inertial frames and that of the matter rotation (r, t) are studied for uniform and non-uniform motions. We find out the restrictions on the radii of the models for real astrophysical situations, and the periods of physical validity of them are also obtained. Rotating models which are expanding as well are obtained, in which cases the rotational velocities are found to decay with the time; and these models may be taken as examples of real astrophysical objects in this Universe.     

On slowly-rotating cosmological viscous-fluid model universes in general relativity

The dynamics of a slowly-rotating cosmological viscous-fluid universe is investigated and the rotational perturbations of such models are studied in order to substantiate the possibility that the Universe is endowed with slow rotation, in the course of presentation of some new analytic solutions. Three different cases are taken up in which the nature and role of the metric rotation (r, t) as well as that of the matter rotation (r, t) are discussed. The periods of physical validity of some of the models and the effect of viscosity on the rotational motion are also found out. Rotating models which are expanding as well are obtained, where in all the cases the rotational velocities are found to decay with the time; and these models may be taken as good examples of real astrophysical situations.     

Rotational perturbations of cosmological viscous-fluid Universe with zero-mass scalar field

Certain new analytic solutions for the rotational perturbations of the Robertson-Walker universe are found out to substantiate the possibility of the existence of a rotating viscous universe with zero-mass scalar field. The values for (r, t) which is related to the local dragging of inertial frames are investigated. In all the cases the rotational velocity is found to decay with time. Except for perfect dragging the scalar field is found to have a damping effect on the rotation of matter. The damping effect is found to be roughly analogous to viscosity. In some solutions it is found that the scalar field may exist only during a time period in the course of evolution of the Universe.     

Cosmological Massive Scalar Field Interacting with Viscous Fluid

Relativistic cosmological field equations are obtained for a Robertson-Walker space time interacting with viscous fluid and massive scalar field. The cosmological solutions to the field equations are obtained and the nature of the scalar field as well as the viscous fluid are studied. It is found that the solutions obtained are realistic only for a closed Universe. This revised version was published online in July 2006 with corrections to the Cover Date.     

Rotating anisotropic two-fluid magnetocharged cosmological models in general relativity

Presenting some interesting new solutions, rotating models of anisotropic two-fluid universes coupled with a magnetic field are investigated and studied, where the anisotropic pressure is generated by the presence of two non-interacting perfect fluids which are in relative motion with respect to each other. Here special discussion is made of the physically interesting class of models in which one fluid is a comoving radiative perfect fluid which is taken to model the cosmic microwave background and the second a non-comoving perfect fluid which will model the observed material content of the universe. Besides studying their physical and dynamical properties the effects of rotation on these models are studied and the reactions of the magnetic and gravitational fields with respect to the rotational motion are discussed. Analysis on the rotational perturbations are also made, in the course of which the amount of anisotropy induced in pressure distribution by a small deviation from the Friedmann metric is also investigated. The models obtained here are found to be theoretically satisfactory and thereby substantiates the possibilities of existence of such astrophysical objects in this Universe and may be taken as good examples of real astrophysical situations.     

Noncommutative branch-cut quantum gravity with a self-coupling inflaton scalar field: The wave function of the Universe

This article focuses on the implications of a noncommutative formulation of branch-cut quantum gravity. Based on a mini-superspace structure that obeys the noncommutative Poisson algebra, combined with the Wheeler–DeWitt equation and Hořava–Lifshitz quantum gravity, we explore the impact of a scalar field of the inflaton-type in the evolution of the Universe's wave function. Taking as a starting point the Hořava–Lifshitz action, which depends on the scalar curvature of the branched Universe and its derivatives, the corresponding wave equations are derived and solved. The noncommutative quantum gravity approach adopted preserves the diffeomorphism property of General Relativity, maintaining compatibility with the Arnowitt–Deser–Misner Formalism. In this work we delve deeper into a mini-superspace of noncommutative variables, incorporating scalar inflaton fields and exploring inflationary models, particularly chaotic and nonchaotic scenarios. We obtained solutions to the wave equations without resorting to numerical approximations. The results indicate that the noncommutative algebraic space captures low and high spacetime scales, driving the exponential acceleration of the Universe.     

Slow rotational perturbations of Robertson-Walker universes

A slow rotation perturbation of Robertson-Walker universes filled with perfect fluid has been investigated. It is found that the unit-four vector of perfect fluid hasno angular velocity in the perturbed cosmological models. The slow rotation which is related to the dragging of the local inertial frames, is compatible only with the cases of positive and negative curvatures of the cosmological universe. The intrinsic velocity vector field of the Universe isexpanding as well asshearing.     

Cosmological scalar fields that mimic the ΛCDM cosmological model

We look for cosmologies with a scalar field (dark energy without cosmological constant), which mimic the standard ΛCDM cosmological model yielding exactly the same large-scale geometry described by the evolution of the Hubble parameter (i.e. photometric distance and angular diameter distance as functions on z). Asymptotic behavior of the field solutions is studied in the case of spatially flat Universe with pressureless matter and separable scalar field Lagrangians; the cases of power-law kinetic term and power-law potential are considered. Exact analytic solutions are found in some special cases. A number of models have the field solutions with infinite behavior in the past or even singular behavior at finite redshifts. We point out that introduction of the cosmological scalar field involves some degeneracy leading to lower precision in determination of Ω _m . To remove this degeneracy additional information is needed besides the data on large-scale geometry. The article is published in the original.     

Nucleosynthesis in bouncing cosmologies

It is shown that certain anomalies connected with the primordial abundances of light nuclei may be resolved if it is assumed that the Universe oscillates between phases of finite densities. Since general relativity does not produce bouncing models of the Universe, such models are obtained through the introduction of a negative energy scalar field of zero rest mass. It is shown that all the relevant parameters of the dynamics of the model and the nucleosynthesis in it are determined by observations and that a self-consistent picture emerges. The model is capable of admitting more than three neutrino flavours without an embarrassingly high primordial helium content. It is also shown that the calculations could be adapted to described production of light nuclei in compact massive bouncing objects.     

Irreversible Matter Creation in Inflationary Cosmology

Irreversible matter creation is investigated in a two-component (scalar field and ordinary matter) cosmological fluid in a homogeneous spatially flat and isotropic Friedmann-Robertson-Walker (FRW) inflationary Universe during its reheating era. The thermodynamics of open systems as applied together with the gravitational field equations to the two-component cosmological fluid leads to a generalisation of the elementary reheating theory in which the decay (creation) pressures are explicitly considered as parts of the fluid stress-energy tensor. Particular models describing coherently oscillating scalar waves and leading to a high particle production at the beginning of the oscillatory period are considered too. This revised version was published online in July 2006 with corrections to the Cover Date.     

Bianchi-II Rotating World

Dynamical and kinematic properties of Bianchi-II cosmological models with rotation and expansion are investigated. Exact solutions of Einstein field equations are obtained which describe the evolution of a rotating Universe. Exact solutions of null, timelike and spacelike geodesics are constructed. Two new cosmological tests for rotating universes are discussed: cosmological lens effect and cosmological mirror effect.     

Slowly-rotating charged viscous-fluid universes: Exact solutions

By considering a spherically-symmetric metric, certain new analytic solutions for charged rotating viscous-fluid cosmological models in the Einstein universe are found out. Five different cases in which the nature and role of the rotational velocity (r, t) is related to the local dragging of inertial frames and that of matter rotation (r, t), are investigated. Except for the case of perfect dragging, the electric field is found to have a damping effect on the rotation of matter. The damping effect is seen to be roughly analogous to the viscosity. In some solutions we find out the temporal restrictions for realistic astrophysical situations. Models which are rotating as well as expanding are also obtained and studied.     

Conformal analogs of the Jordan-Brans-Dicke theory. II. (models including vacuum effects)

This paper is part of a series based on a modified Jordan tensor-scalar theory of gravitation. Given the current importance of research on vacuum phenomena in cosmic evolution, we examine several standard cosmological models with a scalar field and a physical vacuum, including models that have a dominant scalar field with the vacuum energy taken into account in various conformal representations of the Jordan theory, as well as models in which ordinary matter that obeys the conventional equations of state is present. Some noteworthy results are obtained which are, to a certain extent, consistent with currently available observational data.