Particle horizon

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

Structure of the Universe

Abstract: An introductory account is given of the understanding of the structure of the universe. At present the most plausible theory of the origin of the universe is that it formed from the explosion of an extremely hot and dense fireball several billion years ago. During the first few seconds after the big bang, the energy density was so great that only fundamental particles (leptons, quarks, gauge bosons) existed. As the universe cooled and expanded after the big bang, nuclei and atoms formed and condensed into galaxies and stars and systems of them. The fundamental particles and a wide range of gravitational aggregates of them constitute the small-scale and large-scale structure of the present universe. The current knowledge of the elements of the structure of the universe based on the standard big bang model and the standard model of fundamental particles is considered.

Expanding cosmology with back reaction term caused by quantum particle creation

Abstract: An extended Standard cosmological Model is considered with a time dependent cosmological term of the form λ0( ˙ R/dt)/R, R(t) the cosmic scale factor. Such term, that is proportional to the number of quantum particles created by Universe expansion, is introduced to take into account the back reaction to particle creation. The model is first studied when the equation of state p = wρ holds between the energy density ρ and pressure p of the Universe. Exact solutions are determined in the flat space-time case for arbitrary w. The curved space-time cases are solved for w = −1, −1/3. The solutions show the existence of a large variety of possible dynamics of the Universe. The model is studied also when the energy density has the sufficiently general form ρ = ρ0(R/R0) −α . Solutions are given by quadrature. In the flat spacetime case case the quadrature is performed exactly. This shows the existence of an inflationary big-bang at time t = 0 and an accelerated expansion for large t with corresponding particle production. Moreover a numerical determination of the particle creation parameter Ωcr is obtained. In the matter dominated case the value of Ωcr is near to the value of ΩΛ while in the radiation dominated case Ωcr is near to ΩΛ+ΩC where ΩΛ, ΩC are the numerical values of the experimental dark energy and cold dark matter parameters at present time. The model is solved also for ρ =0 ,p � 0. For such unusual situation the value of the ”radius of the Universe” at the present time is calculated

Cosmological constraints on the variable modified Chaplygin gas model by using MCMC approach

Abstract: We investigate the cosmological constraints on the variable modified Chaplygin gas (VMCG) model from the latest observational data: Union2 dataset of Type Ia supernovae (SNIa), the observational Hubble data (OHD), the baryon acoustic oscillations (BAO) and the cosmic microwave background (CMB) data. By using the Markov chain Monte Carlo (MCMC) method, we obtain the mean values of parameters in the flat model: , , , , , and . Furthermore, we investigate the thermodynamical properties of VMCG model at apparent horizon, event horizon and particle horizon respectively.

The Cosmic Causal Mass

Abstract: In order to provide a better understanding of rotating universe models, and in particular the Godel universe, we discuss the relationship between cosmic rotation and perfect inertial dragging. In this connection, the concept of causal mass is defined in a cosmological context, and discussed in relation to the cosmic inertial dragging effect. Then, we calculate the mass inside the particle horizon of the flat ΛCDM-model integrated along the past light cone. The calculation shows that the Schwarzschild radius of this mass is around three times the radius of the particle horizon. This indicates that there is close to perfect inertial dragging in our universe. Hence, the calculation provides an explanation for the observation that the swinging plane of a Foucault pendulum follows the stars.

Cosmic sound: Measuring the Universe with baryonic acoustic oscillations

Abstract: During the last ten to fifteen years cosmology has turned from a data-starved to a data-driven science. Several key parameters of the Universe have now been measured with an accuracy better than 10%. Surprisingly, it has been found that instead of slowing down, the expansion of the Universe proceeds at an ever increasing rate. From this we infer the existence of a negative pressure component -- the so-called Dark Energy (DE) -- that makes up more than two thirds of the total matter-energy content of our Universe. It is generally agreed amongst cosmologists and high energy physicists that understanding the nature of the DE poses one of the biggest challenges for the modern theoretical physics. Future cosmological datasets, being superior in both quantity and quality to currently existing data, hold the promise for unveiling many of the properties of the mysterious DE component. With ever larger datasets, as the statistical errors decrease, one needs to have a very good control over the possible systematic uncertainties. To make progress, one has to concentrate the observational effort towards the phenomena that are theoretically best understood and also least ``contaminated'' by complex astrophysical processes or several intervening foregrounds. Currently by far the cleanest cosmological information has been obtained through measurements of the angular temperature fluctuations of the Cosmic Microwave Background (CMB). The typical angular size of the CMB temperature fluctuations is determined by the distance the sound waves in the tightly coupled baryon-photon fluid can have traveled since the Big Bang until the epoch of recombination. A similar scale is also expected to be imprinted in the large-scale matter distribution as traced by, for instance, galaxies or galaxy clusters. Measurements of the peaks in the CMB angular power spectrum fix the physical scale of the sound horizon with a high precision. By identifying the corresponding features in the low redshift matter power spectrum one is able to put constraints on several cosmological parameters. In this thesis we have investigated the prospects for the future wide-field SZ cluster surveys to detect the acoustic scale in the matter power spectrum, specifically concentrating on the possibilities for constraining the properties of the DE. The core part of the thesis is concerned with a power spectrum analysis of the SDSS Luminous Red Galaxy (LRG) sample. We have been able to detect acoustic features in the redshift-space power spectrum of LRGs down to scales of ~ 0.2 hMpc^{-1}, which approximately corresponds to the seventh peak in the CMB angular spectrum. Using this power spectrum measurement along with the measured size of the sound horizon, we have carried out the maximum likelihood cosmological parameter estimation using Markov chain Monte Carlo techniques. The precise measurement of the low redshift sound horizon in combination with the CMB data has enabled us to measure, under some simplifying assumptions, the Hubble constant with a high precision: H_0 = 70.8 {+1.9} {-1.8} km/s/Mpc. Also we have shown that a decelerating expansion of the Universe is ruled out at more than 5-sigma confidence level.