Spherically symmetric cosmological perturbation in a universe with background field

In a previous paper the equations of small cosmological perturbations of a theory of gravitation in flat space-time are derived. They are applied to a homogeneous, isotropic, nonsingular cosmological model with radiation, matter and background field. At the beginning of the universe small spherically symmetric inhomogeneities on almost all scales can arise by instability. Later on the density contrast of dust grows exponentially during a short time epoch. The solution during this time period is given analytically.     

Spherically symmetric cosmological perturbations in the de Donder gauge (II)

In the framework of a previously developed procedure the evolution of small spherically symmetric perturbations in a homogeneous R-W-F universe is analyzed. It turns out that the evolution tendency is mainly predicted by the state of the cosmic background. In the radiation dominated period the universe does not stimulate growing processes, a perturbation will be in a frozen state or it will diffuse. It is found that a dust dominated universe stimulates the perturbation masses to grow. The rate of this cosmic affected growing process is proportional to (R)^–1/2 (R being the scale factor). Consequently almost all galaxies were formed at the beginning of the dust dominated era.     

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.     

Scalar-tensor theory of gravity and generalized second law of?thermodynamics on?the?event horizon

Here we consider our universe as homogeneous spherically symmetric FRW model and analyze the thermodynamics of this model of the universe in scalar-tensor theory. Assuming the first law of thermodynamics validity of the generalized second law of thermodynamics (GSLT) at the event horizon is examined in both the cases when the universe is filled with perfect fluid and the holographic dark energy.     

Perturbation of the vectorial elements of non-Keplerian orbits

A vector method of treating perturbations of orbits in arbitrary spherically symmetric fields of force is presented. This formulation makes it possible to commence the vector perturbational analysis of motion in an arbitrary non-symmetric field from an intermediate orbit which incorporates all of the spherically symmetric part of the field rather than from a simple Keplerian orbit. Only the nonsymmetric part of the field need then be considered the source of the perturbation.     

Spherically symmetric cosmological perturbations in the de Donder gauge

Cosmological perturbations on a F-R-W background are considered in a modified de Donder gauge. To guarantee the energy-momentum conservation for the perturbations in the de Donder gauge a compatibility condition is obtained. Finally we present the basic equations for the propagation of spherically symmetric perturbations. These equations are the basis for investigating the influence of cosmological epoches on the growing of density contrasts.     

Long-periodic and secular perturbations to the orbit of a spherical satellite due to direct solar radiation pressure

A theory is developed for the perturbations to the orbit of a spherically symmetric satellite which accounts for the changes in the perigee and nodal positions and the variations of the Sun-Earth distance and direction over an orbital revolution. The theory is semi-analytical, the equations of motion being integrated with respect to time over the sunlit period of each orbital revolution. Long-periodic and short-periodic perturbations may be treated separately, and this is important for long-term analyses in terms of mean elements where short-period terms are averaged or omitted.     

Anisotropic Fluid Distribution in Bimetric Theory of Relativity

In this paper we have presented a procedure to obtain exact analytical solutions of field equations for spherically symmetric self-gravitating distribution of anisotropic matter in bimetric theory of gravitation. The solution agrees with the Einstein's general relativity for a physical system compared to the size of universe such as the solar system. This revised version was published online in July 2006 with corrections to the Cover Date.     

Perturbations of a close-Earth satellite due to sunlight diffusely reflected from the Earth

A semianalytic method has been developed to calculate the radiation-pressure perturbations of a close-Earth satellite due to sunlight reflected from the Earth. The assumptions made are that the satellite is spherically symmetric and that the solar radiation is reflected from the Earth according to Lambert's Law with uniform albedo. By using expressions for the components of the radiation-pressure force due to Lochry, the expressions for the perturbations of the elements were developed into series in the true anomalyv. The perturbations within a given revolution can be obtained analytically by integrating with respect tov while holding all slowly varying quantities constant. The long-range perturbations are then obtained by accumulating the net perturbations at the end of each revolution.     

Perturbations of a close-earth satellite due to sunlight diffusely reflected from the Earth

A semianalytical method has been developed to calculate the radiation-pressure perturbations of a close-Earth satellite due to sunlight reflected from the Earth. It is assumed that the satellite is spherically symmetric and that the solar radiation is reflected from the Earth according to Lambert's Law. To account for the increasing reflectivity of the Earth toward the poles, its albedo is assumed to have a latitudinal dependence given bya=a ₀ +a ₂ sin². The effect of the terminator on the perturbations has been neglected. The perturbations within a particular revolution are given analytically, while the long-range perturbations are obtained by accumulation.     

Accretion of holographic dark energy: dependency only upon horizon radius of expanding universe

In this paper we deal with accretion of dark energy in the holographic dark energy model for a general non-rotating static spherically symmetric black hole. The mass of the black hole increases or decreases depending on the nature of the holographic dark energy (quintessence or phantom) as well as on some integration parameters. It is to be illustrated that the enhancement or reduction of mass of a black hole is independent of the mass or size of the black hole itself. Rather it depends only upon the radius of the event horizon of the universe. Finally, the generalized second law of thermodynamics has been studied on the event horizon to be assured that the law holds even if when the black hole mass is decreasing though it is engrossing some mass.     

Dynamics of warm inflation with gauge fields in Bianchi type I universe model

In this paper, we study the dynamics of warm inflation in which slow-roll inflation is driven by non-Abelian gauge fields. To this end, we use the geometry of locally rotationally symmetric Bianchi type I universe model. We construct dynamical equations, i.e., first model field equation, energy conservation equations and equation of motion under slow-roll approximation. In order to discuss inflationary perturbations, we evaluate parameters like scalar and tensor power spectra as well as scalar and tensor spectral indices. We also evaluate inflaton, directional Hubble parameter, slow-roll and perturbation parameters as well as tensor-scalar ratio as a function of inflaton during intermediate and logamediate inflationary eras. It is concluded that anisotropic inflationary universe model with non-Abelian gauge fields remains compatible with WMAP7.     

Charged shell supported by a phantom energy

This paper discusses the evolution of a thin spherically symmetric self gravitating phantom shell around the charged shell. The general equations describing the motion of shell with a general form of equation of state are derived. The different types of space-time R _± and T _± regions and shell motion are classified depending on the parameters of the problem. The mechanical stability analysis of this spherically symmetric thin shell with charge in Reissner-Nordstrom (RN) to linearized spherically symmetric perturbation about static equilibrium solution is carried out.     

Black hole stability in multidimensional gravity theory

Exact static, spherically symmetric solutions to the Einstein-Maxwell-scalar equations, with a dilatonic-type scalar-vector coupling, in D-dimensional gravity with a chain of n Ricci-flat internal spaces are considered. Their properties and special cases are discussed. A family of multidimensional dilatonic black-hole solutions is singled out, depending on two integration constants (related to black hole mass and charge) and three free parameters of the theory (the coordinate sphere, internal space dimensions, and the coupling constant). The behaviour of the solutions under small perturbations preserving spherical symmetry, is studied. It is shown that the black-hole solutions without a dilaton field are stable, while other solutions, possessing naked singularities, are catastrophically unstable.     

2-post-Newtonian approximation of a nonstationary spherically symmetric star in flat space-time theory of gravitation

Starting from a previously stated theory of gravitation in flat space-time the 2-post-Newtonian approximation of a nonstationary spherically symmetric star is derived. The theory forces retarded effects for one part of the solutions of the 2-post-Newtonian approximation. The equations of motion and the conserved total energy of a nonstationary star are given up to 2-post-Newtonian order. The solution in the exterior of the body is studied to this accuracy. Birkhoff's theorem is violated. For the special case of a static spherically symmetric star we get deviations of the exterior solution in the 2-post-Newtonian approximation relative to Einstein's theory.     

Theory of linear cosmological perturbations in flat space-time theory of gravitation

Covariant linear cosmological perturbations are considered in flat space-time theory of gravitation. The background metric is not altered. The perturbed energy-momentum is given. The basic equations for the propagation of the perturbations are presented. The perturbed equations for a homogeneous, isotropic universe are stated.     

Gravitational perfect fluid collapse in f(R) gravity

In this paper, we investigate spherically symmetric perfect fluid gravitational collapse in metric f(R) gravity. We take non-static spherically symmetric metric in the interior region and static spherically symmetric metric in the exterior region of a star. The junction conditions between interior and exterior spacetimes are derived. The field equations in f(R) theory are solved using the assumption of constant Ricci scalar. Inserting their solution into junction conditions, the gravitational mass is found. Further, the apparent horizons and their time of formation is discussed. We conclude that the constant scalar curvature term f(R ₀) acts as a source of repulsive force and thus slows down the collapse of matter. The comparison with the corresponding results available in general relativity indicates that f(R ₀) plays the role of the cosmological constant.     

Anisotropic fluid distribution in higher dimensional general theory of relativity

We have obtained static and spherically symmetric self-gravitating solution of the field equations for anisotropic distribution of matter in higher- dimensional in the context of Einstein’s general theory of relativity. This work is an extension of the previous work of Hector Rago (Astrophys. Space Sci. 183:333, 1991) for four dimensional space-time. The solutions are matched to the analytical solutions for spherically symmetric self gravitating distribution of anisotropic matter obtained by Hector Rago (1991) for n=2.     

Equilibrium problems in a rotating convection zone

This paper is a continuation of the author's work on stellar convection (Vandakurov, 1975a; hereafter referred to as Paper I). The approximate equations for convective perturbations in Paper I are somewhat corrected and generalized to include both nonlinear terms and possible variations in molecular weight. A crude estimate of the nonlinear terms is given by means of an expansion of the solution in powers of the perturbation amplitude. We assume that only the most rapidly growing unstable modes are of significance and that the initial kinetic energy of each independent mode is the same. An expansion in powers of the angular velocity is also performed. (This means that some upper stellar layers with small, but not very small, superadiabaticity are considered.) It is shown that an azimuth-averaged azimuthal force is created by the unstable perturbations. In particular, it is most likely that in the upper part of any stellar convection envelope the rigid rotation is nonequilibrious. A simple formula for the above azimuthal force is derived in the case of a latitudedependent angular velocity and a small viscosity of the medium. If the perturbed characteristic scaleheight is sufficiently small, the azimuthal force created by the most unstable modes is equivalent to a viscous force, but with a negative viscosity coefficient. In the approximation under consideration, the heat flux is spherically symmetric.