Holographic Dark Energy Cosmological Models in f(G) Theory

In this paper, Locally Rotationally Symmetric (LRS) Bianchi type-I models with holographic dark energy within the framework of f(G) theory of gravitation are thought about. So as to get determinate solutions, volumetric exponential expansion, power law expansion and hybrid expansion law are mentioned. The physical interpretations of the solution have been studied by using some physical quantizes. Additionally to make the interpretation more clear for that the statefinder diagnostic pair {r, s} and jerk parameter are analyzed to characterize completely different phases of the universe.     

Higher-Dimensional Anisotropic Modified Holographic Ricci Dark Energy Cosmological Model in Lyra Manifold

Astrophysics - We used modified holographic Ricci dark energy to find anisotropic LRS Bianchi type I cosmological model in five-dimensions based on Lyra geometry. The exact solutions of the...     

Cosmological self-similarity

By use of a simple set of scaling equations it is demonstrated that atomic and stellar systems show evidence of quantitative self-similarity. Six of the basic parameters characterizing the atomic scale, when properly scaled, are nearly identical to the corresponding six basic measurements characterizing the stellar scale. Galactic scale extrapolations are mentioned and a definitive prediction with which to test the principle of self-similarity is identified.     

Zonal-Harmonics Perturbations

A recently developed iterative technique for solving the perturbed Kepler problem is explained, in a step-by-step detail, using the simple example of oblateness perturbations. The results are then extended to deal with higher-degree zonal harmonics.     

Cosmological hadronic fireball

Relativistic Non-Zero Pressure Cosmology describes a hadronic fireball in the primordial stage of the Universe near the singularity. It is phenomenologically matched to Hagedorn's equation of state based on thermodynamics of strong interactions.     

Cosmological considerations regarding Uranus

The cosmogony of Uranus is discussed within the context of a picture in which solid condensed materials accumulate to form a large body, which then acquires significant amounts of gas from the primitive solar nebula. Of prime cosmogonical importance is the tilt of the equatorial plane of the planet and of the plane of tilt of the planet can easily occur as a result of a major collision during the formation process; it seems most likely that the tilt of the satellite orbits requires that they were formed from a gaseous disc rotating about the planet after the tilt of the planetary rotational axis had occurred. Possible methods for tilting this gaseous disc are discussed. A strong early magnetic field may have helped in this and may have played an essential role in showing down the spin of the planet to the present observed value. These processes may have produced significant compositional differences between the satellites of Uranus and those of Jupiter and Saturn.     

Cosmological models of gamma-ray bursts

We review models of cosmological gamma-ray bursts (GRBs). The statistical and -ray transparency issues are summarized. Neutron-star and black-hole merger scenarios are described and estimates of merger rates are summarized. We review the simple fireball models for GRBs and the recent work on non-simple fireballs. Alternative cosmological models, including models where GRBs are analogs of active galactic nuclei and where they are produced by high-field, short period pulsars, are also mentioned. The value of neutrino astronomy to solve the GRB puzzle is briefly reviewed.     

Cosmological constant as integration constant

Einstein's field theory of elementary particles (Einstein 1919) yields black holes with a mass M ˜ G⁻¹ Λ^−1/2c² and a charge Q ˜ G^−1/2λ^−1/2c², their curvatu re radius is Λ^−1/2. Here 4Λ is an integration constant of Einstein's ‘trace-less’ gravitation equations. The choice λ = G⁻¹h⁻¹c³ for this constant defines Planckions and implies “strong gravity”. The choice λ = λ = 3H_inf²c⁻² (where H_inf means the Hubble parameter of a final de Sitter cosmos) involves “weak gravity” and describes an electro-vac spherical universe.     

Some Bianchi Type I Viscous Fluid Cosmological Models with a Variable Cosmological Constant

Some Bianchi type I viscous fluid cosmological models with a variable cosmological constant are investigated in which the expansion is considered only in two direction i.e. one of the Hubble parameter is zero. The viscosity coefficient of bulk viscous fluid is assumed to be a power function of mass density whereas the coefficient of shear viscosity is considered as constant in first case whereas in other case it is taken as proportional to scale of expansion in the model. The cosmological constant Λ is found to be positive and is a decreasing function of time which is supported by results from recent supernovae Ia observations. Some physical and geometric properties of the models are also discussed.     

Cosmological Evolution of Supergiant Star-Forming Clouds

We present the results of very high resolution CDM simulations of galaxy formation designed to follow the formation and evolution of self-gravitating, supergiant star-forming clouds. We find that the mass spectrum of these clouds is identical to that of globular clusters and GMCs; dN/dM ∝ M ^-1.7 ± 0.1. This revised version was published online in September 2006 with corrections to the Cover Date.     

Cosmological parameters and cosmic topology

Geometry constrains but does not dictate the topology of the three-dimensional space. In a locally spatially homogeneous and isotropic universe, however, the topology of its spatial section dictates its geometry. We show that, besides determining the geometry, the knowledge of the spatial topology through the circles-in-the-sky offers an effective way of setting constraints on the density parameters associated with dark matter (Ω_m) and dark energy  (Ω_Λ)  . By assuming the Poincaré dodecahedral space as the circles-in-the-sky detectable topology of the spatial sections of the Universe, we re-analyse the constraints on the density parametric plane  Ω_m–Ω_Λ  from the current Type Ia supernova plus X-ray gas mass fraction data, and show that a circles-in-the sky detection of the dodecahedral space topology gives rise to strong and complementary constraints on the region of the density parameter plane currently allowed by these observational data sets.     

Cosmological parameters and redshift periodicity

This work is the continuation of the search for such a cosmological model using which the observed redshift distribution of galaxies in the sample of Broadhurstet al. (1990) turns out to be maximally periodic in the calculated spatial distance. In a previous work, Paálet al. (1992) have demonstrated that among theflat models with non-negative cosmological constant (e.e., vacuum density) the one with a vacuum: dust ratio 2:1 provides the optimum. Now we extend that study to the case of arbitrary space curvature and find equally good periodicity in a surprisingly wide range of models. By use of the dimensionless parameters ₀= ₀/ _crit and ₀=/3H ₀ ² acceptable periodicity is obtained forall points of the parameter plane within the strip between the parallel lines 0.83₀–0.30< ₀(₀)<0.83₀+0.85(₀<1.8), whilst the best periodicities appear along the line ₀=0.83₀+0.39 fitting to the previous optimum at ₀=1/3, ₀=2/3. Any nonpositive value of ₀ gives bad periodicity unless the space curvature is strongly negative and ₀<0.4. Fairly good periodicity is observed only in the range of the deceleration parameter –1.2q ₀<0.2, corresponding to a small or even negative total gravitational attraction and an expansion time-scale longer than usually expected.     

Cosmological constraint on Brans-Dicke Model

We combine new Cosmic Microwave Background(CMB) data from Planck with Baryon Acoustic Oscillation(BAO) data to constrain the Brans-Dicke(BD) theory,in which the gravitational constant G evolves with time.Observations of type Ia supernovae(SNe Ia) provide another important set of cosmological data,as they may be regarded as standard candles after some empirical corrections.However,in theories that include modified gravity like the BD theory,there is some risk and complication when using the SNIa data because their luminosity may depend on G.In this paper,we assume a power law relation between the SNIa luminosity and G,but treat the power index as a free parameter.We then test whether the difference in distances measured with SNIa data and BAO data can be reduced in such a model.We also constrain the BD theory and cosmological parameters by making a global fit with the CMB,BAO and SNIa data set.For the CMB+BAO+SNIa data set,we find 0.08 × 10~(-2) ζ 0.33 × 10~(-2) at the 68% confidence level(CL) and-0.01 × 10~(-2) ζ 0.43 × 10~(-2) at the 95% CL,where ζ is related to the BD parameter ω by ζ = ln(1 + 1/ω).     

Cosmological evolution of pilgrim dark energy

We study pilgrim dark energy model by taking IR cut-offs as particle and event horizons as well as conformal age of the universe. We derive evolution equations for fractional energy density and equation of state parameters for pilgrim dark energy. The phantom cosmic evolution is established in these scenarios which is well supported by the cosmological parameters such as deceleration parameter, statefinder parameters and phase space of ω _? and \(\omega'_{\vartheta}\) . We conclude that the consistent value of parameter μ is μ<0 in accordance with the current Planck and WMAP9 results.