Particle horizon

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

Primordial gravitational waves in the inflationary universe model, and the grand unification scale

Abstract: The amplification of vacuum metric fluctuations corresponding to gravitational waves is analyzed in the inflationary universe model. The primordial gravitational-wave spectrum is so chosen as to be independent of the detailed history of the universe after the phase transition. The inflationary scenario will be compatible with experimental data on the anisotropy of the cosmic microwave background only if the vacuum energy density of the symmetric phase is much lower than the Planck value.

High Momentum Behavior of Geometric Bremsstrahlung in the Expanding Universe

Abstract: •We discuss various kinds of geometric bremsstrahlung processes in the spatially flat Robertson· Walker universe. Despite the fact that the temperature of the universe is much higher than particle masses and the Hubble parameter, the transition probability of these processes does not vanish. It is also pointed out that explicit forms of the probability possess a new duality with respect to the scale factor of the background geometry. Particles in the early universe undergo severe redshift as a result of the cosmic expansion and become decelerated extraordinarily in comoving coordinates. Conse­ quently radiation or massless particles may be emitted from the decelerated particle. This process induced by the geometry of the universe is regarded as a kind of bremsstrahlung. We call this a geometric bremsstrahlung. This effect may bring about many sorts of decay and emission processes which are prohibited kinematically in flat spacetime. Despite its ability to realize such a process in the classical mechanical sense, there is a nontrivial aspect of the existence of quantum geometric bremsstrahlung. Tem­ perature in many interesting situations of the early universe is much higher than particle masses and the Hubble parameter. Since the momenta of the particles are comparable with the temperature, one might naively think that we can neglect all the mass parameters even in calculation of the transition probabilities. Hence it might be expected that the probability of the process is equal to that calculated in massless theories in the flat spacetime, and thus exactly zero. However, this naive expectation turns out to be wrong under careful analysis. In Ref. 1), the first precise analysis was performed in the four dimensional Robertson-Walker universe. The authors of that paper showed that even in the high momentum limit there remains the nonvanishing probability of photon emission via geometric bremsstrahlung. In this paper we give an extended analysis of several kinds of processes of geometric bremsstrahlung. This includes analyses of the ifi theory in arbitrary dimensional spacetimes, the theory with a Yukawa interaction, and the massive vector field theory. It will be shown that the high momentum limit, or the high temperature limit, does not result in the termination of the geometric bremsstrahlung process in a rather wide class of interactions and in arbitrary dimension. It is also stressed that a new type of duality can be found in the forms of the transition probabilities for renormalizable interactions. In § 2 we introduce the spatially flat Robertson-Walker universe with past and

Cosmological Constraints on a Massive Neutrino

Abstract: The paper by Sato and Kobayashi in 1977 studied the cosmological effects of a massive neutrino and obtained constraints on its properties. This paper initiated many studies to use cosmology as a laboratory of particle physics or to use particle physics to explore the very early universe. Subject Index: 154, 177, 416

Cosmological Distances in Closed Model of the Universe

Abstract: Four Cosmological distances were determined in the light of the closed cosmic model which was presented in a previous study. Each of these distances was obtained in terms of the redshift of an extragalactic object. It is found that the luminosity distance of the extragalactic object in the closed cosmic model, the observed model and model are approximately the same up to z = 0.1535. However, the luminosity distance in the close cosmic model approximately agrees with its value in the observed model up to z = 0.6442. Estimations of the horizon distance of the universe, the total mass and the mass of matter within the horizon distance, the equivalent numbers of the Milky Way-like galaxies and the Coma-like clusters of galaxies to the mass of matter were computed in the closed cosmic model at the present time.

Possible Role of Antimatter Galaxies for the Stability of the Universe

Abstract: Recent mathematical, theoretical and experimental studies have confirmed via measurements on Earth Zwicky's hypothesis according to which the cosmological redshift is due to galactic light losing energy to intergalactic media without the expansion of the universe. The main problem of the ensuing return to a static universe is the inevitable prediction that the universe should collapse due to gravitational attractions among galaxies. In this paper, we review the historical inability by general relativity to achieve a stable universe solely composed of matter, and present apparently for the first time a cosmological model in which the universe achieves stability under the condition of admitting an equal number of matter and antimatter galaxies at such a large mutual distance for which gravitational interactions are ignorable.