Particle horizon

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

Inflation in curved model universes with noncritical density

Abstract: Non.flat Friedmann-Lemaitre models solving the horizon problem in which, prior to and during inflation, cumat~re, cosmological constant and radiation are taken into account, are constructed Tor present density parameter values in the range 0.360,s 1.5. The presentation is based on an exact solution 10 the Lemaitre equation containing the three abave.mentioned contributions. Then the influence of matter different from radiation is discussed. We also Sive an example For what happens when the expansion is anisotropic. The large-scale structure of the universe is successfully represented by a Robertson- Walker ( RW) spacetime filled with matter and radiation obeying Einstein's field equation. Such models, being based on the a priori assumptions of spatial homogeneity and isotropy, cannot explain these two fundamental properties which are well supported particularly by the observed isotropy of the 3 K background radiation. Even if one assumes homogeneity and isotropy of spacetime, an explanation of the corresponding properties of marter and radialion in terms of transport processes fails because the comoving radius ud of the particle horizon at the time of decoupling Id, the 'primeval particle horizon', is much smaller than the comoving radius U, of that part of the universe which became visible at decoupling, the 'visual horizon'. Elementary particle theories assume the existence of scalar fields in the very early phases of the universe. These scalar fields can simulate a cosmological constant ( 11. If these scalar fields decay long before decoupling, the horizon problem can be solved, as first pointed out by Guth (?I. The solution of the horizon problem and related problems make inflationary cosmology attractive. It has been claimed that inflation yields a very small spatial curvature. In fact most calculations in inflationary cosmology have been done with a flat RW metric. Also it has been predicted that this vanishing spatial curvature can be used to test inflation (3, 41. Ellis has shown, however, with a simple model that it is possible to solve the horizon problem in cosmological models with an inflationary phase and to get a non-negligible curvature today. In these models the present value of the density parameter n= ~p,,,,/3H' does not have to equal 1 to high accuracy, either. Below we present an improved model supporting the essential conclusions of Ellis. Our model takes into account the effects of radiation and curvature at all times. Moreover, we avoid the unphysical discontinuity of source terms at the onset of inflation used by Ellis for computational simplicity. In contrast to Ellis', our model yields only a lower bound for the expansion during the inflationary phase. If used as a background model for fluctuations of the scalar field, it can therefore be adjusted even if the fluctuation calculations lead to larger lower bounds for the amount of inflationary expansion.

A Machian solution of the hierarchy problem

Abstract: The new interpretation of Mach’s principle of mass of a particle being a measure of the interactions of this particle with all other gravitating particles inside its causal spheres is introduced. It is shown that within some alternative model of gravitation that incorporates this principle, the Machian influence of the universe can reduce Planck’s scale to the electro-weak scale and the large number that is needed to explain the hierarchy between the scales is the amount of gravitating particles inside the universe horizon. Our model can lead to new observable effects at cosmological distances and close to the sources of a strong gravitational field.

Why is the temperature of the universe 2.726 Kelvin

Abstract: The Cosmic Background Explorer satellite has recently made the most accurate measurement of the temperature of the universe, determining it to be 2.726 ± 0.01 kelvin. In trying to understand why the temperature has this value, one is led to discover the most fundamental features of the universe—an early, radiation-dominated epoch, enormous entropy per nucleon, synthesis of the light elements around 3 minutes after the bang, and a small excess of matter over antimatter—as well as some of the most pressing issues in cosmology today—the development of structure in the universe and the identification of the nature of the ubiquitous dark matter.

An Atomic Model of the Early Universe

Abstract: The paper studies a quantum theory of the early Universe with a negative effective cosmological constant.

Radiation accretion by primordial black holes in the early universe

Abstract: The growth of a black hole by radiation accretion in the early Universe is analyzed in the particular case in which the inflow of radiation is purely radial. This is done by generalizing the Einstein-Strauss vacuole model to the case of a radiation-filled universe. It is shown that, under this circumstance, the black hole tends to grow at the same rate as the particle horizon of the universe; this corresponds to an upper limit to the accretion rate.