Bianchi type III models with anisotropic dark energy

The general form of the anisotropy parameter of the expansion for Bianchi type-III metric is obtained in the presence of a single diagonal imperfect fluid with a dynamically anisotropic equation of state parameter and a dynamical energy density in general relativity. A special law is assumed for the anisotropy of the fluid which reduces the anisotropy parameter of the expansion to a simple form (D μ H^-2V^-2{\Delta\propto H^{-2}V^{-2}}, where Δ is the anisotropy parameter, H is the mean Hubble parameter and V is the volume of the universe). The exact solutions of the Einstein field equations, under the assumption on the anisotropy of the fluid, are obtained for exponential and power-law volumetric expansions. The isotropy of the fluid, space and expansion are examined. It is observed that the universe can approach to isotropy monotonically even in the presence of an anisotropic fluid. The anisotropy of the fluid also isotropizes at later times for accelerating models and evolves into the well-known cosmological constant in the model for exponential volumetric expansion.     

Inflationary Scenario in Bianchi Type I Space-Time

Inflationary scenario in Bianchi Type I space-time is discussed. To get the deterministic model of the universe, it has been considered that the energy-momentum tensor of particles ∼T ⁴, almost vanishes in the course of expansion of universe and total energy-momentum tensor reduces to vacuum stress tensor. This leads to a∼e ^Ht where a is scale factor and H the Hubble constant and effective potential V(φ)=constant where φ is Higg’s field and n is a constant. The physical and geometrical aspects of the model in the context of inflationary scenario are also discussed.     

Mass hierarchy from many domain walls

We construct a new model with exponential mass hierarchy by starting with the Einstein–Hilbert action with the cosmological constant in five dimensions plus an action describing many domain walls in four dimensions. The model includes many hidden sectors and one visible sector, and each four-dimensional domain wall, that is, 3-brane, interacts with one another through only a gravitational interaction and realizes many universe cosmology inspired by D-brane perspective. It is shown that in the present model only even numbers of domain walls are allowed to locate in five dimensional space-time and the validity of Randall–Sundrum scenario, which explains mass hierarchy between the Planck mass and the electro-weak scale in our world, depends on a relative relation between our world and hidden worlds.     

Spacetime Curvature is Important for Cosmology Constrained with Supernova Emissions

We investigate universe expansion models as functions of emission frequency ratio decline rather than redshift z, using the latest on-line, self-consistent data from 192 supernovae. We present results for simpler and some current models of cosmology, including those with dark energy (standard model) and a recent model correcting for the effect of a small time-dependent, emission frequency increase with lookback. This new model, with a gentle lookback decline of the Planck constant, and the standard model fit the data with similar confidence according to Bayesian Information Criteria. The standard model tends towards solutions high in matter density while remaining flat, but models without dark energy tend towards dilute universes with significant spacetime and curvature and a smaller Hubble constant. We conclude the normalized spacetime parameter, Ω _k , should not be ignored and it includes the combined contributions of huge spacetime magnitude and curvature.     

The weight,shape, and speed of the universe

Present astronomical data indicate an unbound universe with density ～1.6 × 10^?31 g cm^?3 in which galaxies could not have formed gravitationally. We show how magnetohydrodynamic (MHD) processes allow galaxy formation in an open anisotropic MHD universe with shear, rotation, and fluid flow. The dipole anisotropy of the microwave background radiation sets their respective first-order values at 3.7×10^?15 yr^?1, 10^?14 yr^?1, and 5×10^?4 c. Second-order effects of Maxwell and Reynolds stresses require that the magnetic field, shear, and Hubble expansion be 10^?8 G, 3.7×10^?15 yr^?1, and 10^?10 yr^?1 (100 km sec^?1 Mpc^?1). The model is rigidly self-consistent, predicting both the recent value of the Hubble expansion above and of the shear (? 9×10^?15 yr^?1) given by the microwave background's recently measured quadrupole anisotropy.     

f(R) theories of gravity in the Palatini approach matched with observations

We investigate the viability of f(R) theories in the framework of the Palatini approach as solutions to the problem of the observed accelerated expansion of the universe. Two physically motivated popular choices for f(R) are considered,: power law, f(R) = β R ⁿ , and logarithmic, f(R) = α ln R. Under the Palatini approach, both Lagrangians give rise to cosmological models comprising only standard matter and undergoing a present phase of accelerated expansion. We use the Hubble diagram of type Ia Supernovae and the data on the gas mass fraction in relaxed galaxy clusters to see whether these models are able to reproduce what is observed and to constrain their parameters. It turns out that they are indeed able to fit the data with values of the Hubble constant and of the matter density parameter in agreement with some model independent estimates, but the today deceleration parameter is higher than what is measured in the concordance ΛCDM model.     

The Planck Aether model for a unified theory of elementary particles

A dense assembly of an equal number of two kinds of Planck masses, one having positive and the other one negative kinetic energy, described by a nonrelativistic nonlinear Heisenberg equation with pointlike interactions, is proposed as a model for a unified theory of elementary particles. The dense assembly of Planck masses leads to a vortex field below the Planck scale having the form of a vortex lattice, which can propagate two types of waves, one having the property of Maxwell's electromagnetic and the other one the property of Einstein's gravitational waves. The waves have a cutoff at a wavelength equal to the vortex lattice constant about 10³ times larger than the Planck length, reproducing the GUT scale of elementary particle physics. The vortex lattice has a resonance energy leading to two kinds of quasiparticles, both of which have the property of Dirac spinors. Depending on the resonance energy, estimated to be 10⁷ times smaller than the Planck energy, the mass of one of these quasiparticles is about equal to the electron mass. The mass of the other particle is much smaller, making it a likely candidate for the much smaller neutrino mass. Larger spinor masses occur as internal excitations, with a maximum of four such excitations corresponding to a maximum of four particle families. Other vortex solutions may describe the quark-lepton symmetries of the standard model. All masses, with the exception of the Planck mass particles, are quasiparticles for which Lorentz invariance holds, with the Galilei invariance at the Planck scale dynamically broken into Lorentz invariance below this scale. The assumed equal number of Planck masses with positive and negative kinetic energy makes the cosmological constant exactly equal to zero.     

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.     

The gauge in general relativity. III

A noncustomary gauge theory of general relativity, developed in detail in the preceding paper (II), is here applied to cosmology. A universe that is homogeneous and isotropic in the customary gauge, is considered-first generally, and then in more detail for the case where the noncustomary universe is matter dominated and static. With a particular choice of equation, this model is solved and a new relation between customary mass density, Hubble constant, and deceleration parameter is found. For a customary deceleration parameter of 1.98, this relation yields a customary mass density of 3.1×10^–31 g/cm³-in good agreement with experiment. Finally, the age of the universe in this model is found to be>6.6× 10⁹ yr, again in agreement with other estimates.     

Remarks on the Idea of Spontaneous Break-Down of Symmetry,Cosmic Variability of Eddington's Number,Mach's Idea Concering the Origin of Inertia,and Field Equations Describing Global and Local Gravitational Fields

Subject is considered on the level of classical field theory. We start from some aspects of the theory of ferromagnets. Their counterpart in classical field theory is pointed out using the over simplified model of a selfinteracting scalar field. The ground state (“vacuum expection value”) of the scalar field is interpreted as cosmic background field, which can be considered as constant for local physical phenomena. In practice, however, it is a function of the age of universe. Which kind of function it could be is suggested by a discussion of the cosmic variability of Eddington's number γ = 10⁴⁰, which refers to Dirac's consideration of this problem. But contrary to Dirac's assumption that atomic quantities are constant, we suppose that the inertial mass of elementary particles is a function of the age of universe. The cosmic gravitational field is described by other equations than the gravitational field created by local matter distributions. The field equations for the local gravitational field we start from reduce to Einstein's equations, if we neglect the possible influence of the universe on local phenomena. In case that the cosmic matter is homogeneously and isotropically distributed, the field equations for the cosmic gravitational field permit only such a time dependent solution the three-spaces of which are linearly expanding and spherically closed. The different field equations for cosmic and local gravitational fields are considered approximations of more fundamental field equations which approximately split into two sets of equations, if it is possible to contrast local physical systems with the universe. The described cosmological model taken as a basis, the inertial mass of elementary particles becomes a function of the matter density creating the cosmic gravitational field. This could be considered as, at least, partly realisation of Mach's idea concerning the origin of inertia. Starting from the interpretation of the ground state (vacuum expection value) as a function of a certain cosmic background field, more realistic gage field models could give the following picture of cosmic development: In the far past there was a state of the universe characterized by enormous contraction of matter. In this stage of development, it was impossible to contrast particles with the universe. Matter expands and it becomes possible to contrast certain physical systems with the universe. But the ground state is such a symmetric one that only fields with vanishing rest mass can be contrasted with the universe (ferromagnet above Curie temperature). With further expansion of the universe the ground state will lose certain symmetry properties. By this it becomes possible that you get the impression there are particles with nonvanishing rest mass (ferromagnet below Curie temperature). Finally, the influence of the universe on local physical systems goes to zero with further expansion. Especially, this means the inertial mass of elementary particles goes to zero, too (Curie temperature of ferromagnetic material goes to zero with cosmic expansion).     

Thermodynamic Gravity and the Schrödinger Equation

We adopt a formulation of the Mach principle that the rest mass of a particle is a measure of it’s long-range collective interactions with all other particles inside the horizon. As a consequence, all particles in the universe form a ‘gravitationally entangled’ statistical ensemble and one can apply the approach of classical statistical mechanics to it. It is shown that both the Schrödinger equation and the Planck constant can be derived within this Machian model of the universe. The appearance of probabilities, complex wave functions, and quantization conditions is related to the discreetness and finiteness of the Machian ensemble.     

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.     

Effect of density fluctuations on the expansion of the universe far from the singularity

The effect of fluctuations in the density of matter on the expansion of the universe far from the singularity is analyzed on the basis of a model with a three-dimensional space which is homogeneous and isotropie on the average. The fluctuations reduce the gravitational effect, retarding the expansion. This effect of the fluctuations increases as the expansion proceeds and can strongly affect the expansion velocity. An equation is derived for the age of the universe on the basis of this model. The age is expressed in terms of observable quantities: the Hubble constant and the acceleration parameter. It is shown that fluctuations lead to an increase in this age. It is concluded that fluctuations must be taken into account in studying the expansion of the observable universe.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 1, pp. 7–11, January, 1977.     

Viscous Fluid Cosmology in Bianchi Type-I Space-Time

The paper presents a spatially homogeneous and anisotropic Bianchi type-I cosmological model consisting of a dissipative fluid. The field equations are solved explicitly by using a law of variation for mean Hubble parameter, which is related to average scale factor and yields a constant value for deceleration parameter. We find that the constant value of deceleration parameter describes the different phases of the evolution of universe. A barotropic equation of state (p=γ ρ) together with a linear relation between shear viscosity and expansion scalar, is assumed. It is found that the viscosity plays a key role in the process of the isotropization of the universe. The presence of viscous term does not change the fundamental nature of initial singularity. The thermodynamical properties of the solutions are studied and the entropy distribution is also given explicitly.     

Tachyon field in cosmology

We study cosmological effects of homogeneous tachyon field as dark energy. We concentrate on two different scalar field potentials, the inverse square potential and the exponential potential. These models have a unique feature that the matter density parameter and the density parameter for tachyons remain comparable for a large range in red-shift. It is shown that there exists a range of parameters for which the universe undergoes an accelerated expansion and the evolution is consistent with structure formation requirements. For a viable model we require fine tuning of parameters comparable to that in ACDM or in quintessence models. For the exponential potential, the accelerated phase is followed by a phase witha(t) α t ^2/3 thus eliminating a future horizon.     

Anisotropic Dark Energy Bianchi Type-II Cosmological Models in Lyra Geometry

The spatially homogeneous and totally anisotropic Bianchi type-II cosmological model has been discussed in general relativity in the presence of a hypothetical anisotropic dark energy fluid with constant deceleration parameter within the frame work of Lyra’s manifold with uniform and time varying displacement field vector. With the help of special law of variation for Hubble’s parameter proposed by Bermann (Nuovo Cimento 74B:182, 1983) a dark energy cosmological model is obtained in this theory. We use the power law relation between average Hubble parameter H and average scale factor R to find the solution. The assumption of constant deceleration parameter leads to two models of universe, i.e. power law model and exponential model. Some physical and kinematical properties of the model are also discussed.     

Graviton creation in the inflationary universe and the grand unification scale

The creation of gravitons in the inflationary universe and their effects on the 3K photon background are considered. It is shown that the inflationary universe scenario is compatible with existing experimental data on the large scale anisotropy of relic photons only if the energy density of the symmetric vacuum is much less than the Planck energy density, ?_V < 3 × 10^?8M_pl⁴. This implies an upper bound on the grand unification scale.     

Is Galaxy Dark Matter a Property of Spacetime?

We describe the motion of a particle in acentral field in an expanding universe. Use is made ofa double expansion in 1/c and 1/, where c and are the speed of light and the Hubble time. In thelowest approximation the rotational velocity is shownto satisfy v⁴ = 2/3 GMcH₀, whereG is Newton's gravitational constant, M is the mass ofthe central body (galaxy), and H₀ is theHubble constant. This formula satisfies observations of stars moving inspiral and elliptical galaxies, and is in accordancewith the familiar Tully–Fisher law.     

非奇异宇宙的理想气体自相似模型

通过引力作用下理想气体运动连续性方程的无量纲化,根据量纲理论Π定理,以尺度因子R(t)为物理量统一度量基准,发现了引力作用下理想气体宇宙模型的自相似性和一系列R(t)的解析解.基于R(t),可建立对应的、具有非欧氏几何特性的均匀膨胀时空坐标系S(t,ξ,θ,φ),并获得一个密度ρ为常数、速度u为零、压强p不为零的理想气体宇宙解.在这个解的形式中,光子红移量z所表现的是光子传播距离r,当红移量z较小时两者成正比(即哈勃定律).由均匀膨胀坐标系还可推导出Robertson-Walker度规(k= 关键词： 宇宙 自相似 哈勃定律