Particle horizon

About: Particle horizon is a research topic. Over the lifetime, 2096 publications have been published within this topic receiving 69137 citations.

Explaining the accelerated expansion of the Universe by particle creation

Abstract: A spatially flat FRW Universe in the context of particle creation has been discussed by assuming a variable deceleration parameter which is a function of scale factor. A dust model in which creation of particles giving a negative creation pressure has been studied. Treating the Universe as an open adiabatic system, it is supposed that matter creation takes place out of gravitational energy. In this model, the Universe shows an accelerating phase of its expansion. Total number of particles increases while number of particle density decreases. Some physical implications of this model are investigated.

The Best-Fit Universe

Abstract: Inflation provides very strong motivation for a flat Universe, Harrison-Zel’dovich (constant-curvature) density perturbations, and cold dark matter. However, there are a number of cosmological observations that conflict with the predictions of the simplest such model—one with zero cosmological constant. They include the age of the Universe, dynamical determinations of Ω, galaxy-number counts, and the apparent abundance of large-scale structure in the Universe. While the discrepancies are not yet serious enough to rule out the simplest and “most well motivated” model, the current data point to a “best-fit model” with the following parameters: ΩB Ω 0.03, QCDM Ω 0.17, ΩΛ Ω 0.8, and H o ≃ 70 km sec-1 Mpc-1, which improves significantly the concordance with observations. While there is no good reason to expect such a value for the cosmological constant, there is no physical principle that would rule such out.

The birth of a closed universe, and the anthropogenic principle

Abstract: A scenario is proposed for the evolution of the universe, starting with the quantum birth of a closed world at a minimum in the self-consistent de Sitter cosmological solution with vacuum polarization. The closure of the universe and the permanently supercritical value of its density follow directly from a single condition: that quantum birth take place. The perturbations must be small in order that the de Sitter phase may be sufficiently prolonged to ensure a protracted Friedmann plasma-matter expansion. Thus a universe having the properties we observe may in fact have been singled out by the anthropogenic principle.

Local inhomogeneities in a Robertson-Walker background. III - Elementary growth rates in a flat background with a relativistic equation of state

Abstract: The growth of a class of inhomogeneities embedded in a spatially flat Robertson-Walker background is examined. The inhomogeneities are restricted by the simplifying assumption that the isotropic pressure, as measured along the associated boundary surface, equals the local energy flux. The background is described both by means of a noninteracting mixture of blackbody photons and dust, and by means of a baryon-conserving equilibrium mixture of blackbody photons and a neutral, two-component, relativistic Maxwell-Boltzmann gas. We compare the resultant mass of the inhomogeneities with the Jeans and particle horizon mass scales and demonstrate the critical effect that varying the initial photon-to-baryon ratio in the background has on all masses.

The CMB Dipole and Circular Galaxy Distribution

Abstract: The validity of Hubble's law defies the determination of the center of the big bang expansion, even if it exists. Every point in the expanding universe looks like the center from which the rest of the universe flies away. In this paper, we show that the distri- bution of apparently circular galaxies is not uniform in the sky and that there exists a special direction in the universe in our neighborhood. The data is consistent with the assumption that the tidal force due to the mass distribution around the universe center causes the deformation of galactic shapes depending on its orientation and location relative to the center and our galaxy. Moreover, the CMB dipole data can also be associated with the center of the universe expansion, if the CMB dipole at the center of our supercluster is assumed to be due to Hubble flow. The location of the center is estimated from the CMB dipole data. The direction to the center from both sets of data is consistent and the distance to the center is computed from the CMB dipole data.