Particle horizon

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

A higher-dimensional Bianchi type-I inflationary Universe in general relativity

Abstract: A five-dimensional Bianchi type-I inflationary Universe is investigated in the presence of massless scalar field with a flat potential. To get an inflationary Universe, a flat region in which the potential V is constant is considered. Some physical and kinematical properties of the Universe are also discussed.

The large-scale structure of the Universe

Abstract: The search for a theory that explains the origin of galaxies and large-scale structure in the Universe is at an exciting stage. Observational advances, including measurements of the anisotropy in the cosmic microwave background and systematic surveys of galaxy redshifts, are confronting theoretical calculations of the distribution of matter produced by the action of gravity on small initial density fluctuations in the expanding Universe. Although the basic idea behind most theoretical models is simple, the details are complicated and there are many unknown parameters, such as the quantity and type of dark matter forming the bulk of the mass of the Universe. Consequently, at present, there are a number of contenders for a theory of structure formation but no single model can fit all the observational data completely satisfactorily.

Initial monopole density in an inflationary Universe

Abstract: Non-equilibrium dynamics leading to the formation of topological defects in a symmetry-breaking phase transition is studied. In a spatially flat inflationary Universe an initial number density of monopoles as a function of metric characteristic is estimated. PACS numbers: 1127, 9880B, 9880C 1. Context The first moments of the Universe when the classical description of the spacetime is valid are crucial for our understanding of the present shape of the Universe. It seems that in the early hot Universe as a consequence of expansion and cooling a number of phase transitions occurred. A symmetry-breaking phase transition can produce topological defects which are relics of the symmetric phase of the field theory [1]. Such frozen-out relics of the distant past come in three basic varieties: monopoles, strings and domain walls. The kind of defects which will be left behind by the transition depends on the homotopy group of the manifold of the degenerate broken symmetry vacua [2]. The early stages of the Universe are described within a paradigm of cosmological inflation [3]. Inflation plays three key roles in modern cosmology. The first, is in providing a theory for the origin of perturbations in the Universe. These perturbations are believed to evolve into all the observed structures in the present Universe, including the existence and clustering of galaxies and the anisotropy in the cosmic background radiation. The second, is in setting the initial conditions for the Universe, by arranging a large homogenous Universe. In fact, inflation makes the Universe homogenous and isotropic on the large scale by making cosmic rotation and expansion anisotropies very small on the largest scales [4]. The last role is in diluting defects formed before a period of inflation to such a degree that their number density stays below the observable limits. Among other defects the most troublesome are monopoles which are an inevitable outcome of breaking GUT symmetry. The reason for the monopole problem lies in the monopole mass, which would dominate the Universe and force it to recollapse well before the present era. All of these roles are realized by a period of enormous acceleration of an expansion of the Universe.

Hidden dimensions of the large scale universe and isotropy of the cosmic microwave background radiation

Abstract: It is suggested to resolve the contradiction between the two main cosmological observations of the high isotropy of the cosmic microwave background and fractal structure of the large-scale universe by consideration of a hidden support dimension of the multifractal space-luminous distribution of visible matter in the Perseus-Pisces redshift survey. It is shown that while a simple set given by the galaxy space positions has a support dimension ${D}_{0}\ensuremath{\simeq}2$ inclusion of the galaxy mass (luminosity) leads to a multifractal distribution which can be characterized by two different support dimensions. One of them (corresponding to comparatively rare visible matter) is close to two, whereas the second (corresponding to comparatively dense visible matter) is close to three. The crossover between these two states can be considered as a morphological phase transition.