Particle horizon

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

Chapter 5 – The Birth of the Universe and Dark Energy

Abstract: The theory of the birth of the Universe in the frame of nonlocal quantum hydrodynamics is considered. The transport equations for the physical vacuum (PV) are delivered. The calculations demonstrate that PV equations for “empty” space have the traveling wave solutions belonging, in particular, to the soliton class. The possible influence and reaction of the background microwave radiation is taken into account. These results lead to the principal correction of the inflation theory and serve as the explanation for the recently discovered Universe's cosmic microwave background anomalies. The simple analytical particular cases and numerical calculations are delivered. The analogue of the Hubble effect in the PV boxes is demonstrated.

Spherical Domain Wall Collapse in a Dust Universe

Abstract: To clarify observational consequence of bubble nucleations in inflationary era, we analyse dynamics of a spherical domain wall in an expanding universe. We consider a spherical shell of the domain wall with tension $\sigma$ collapsing in a spherically-symmetric dust universe, which is initially separated into the open Friedmann-Lema\^itre-Robertson-Walker universe inside the shell and the Einstein-de Sitter universe outside. The domain wall shell collapses due to the tension, and sweeps the dust fluid. The universe after the collapse becomes inhomogeneous and is described by the Lema\^itre-Tolman-Bondi model. We construct solutions describing this inhomogeneous universe by solving dynamical equations obtained from Israel's junction conditions applied to this system. We find that a black hole forms after the domain wall collapse for any initial condition, and that the black hole mass at the moment of its formation is universally given by $M_{\rm BH}\simeq 17 \sigma/H_{\rm hc}$, where $H_{\rm hc}$ is the Hubble parameter at the time when the shell radius becomes equal to the Hubble radius. We also find that the dust fluid is distributed as $\rho\propto R^{3/2}$ near the central region after the collapse, where $R$ is the area radius. These features would provide observable signatures of a spherical domain wall generated in the early universe.

The Early Universe, the Present Universe

Abstract: Almost ten years ago Gasperini and Veneziano proposed a new picture of the very primordial Universe (z ≫ 1) based on string theory, called the pre-big-bang scenario. Here we review the key ideas of this model, its main phenomenological consequences, and the most striking differences with respect to ordinary inflationary models. The second part of this Proceedings is concerned with cosmology at much lower redshifts, z < 2. We tackle the problem of the motion of inspiraling and merging black-hole binaries, which are among the most promising astrophysical sources of gravitational waves. We discuss a new approach for the two-body problem in general relativity, which makes it possible to study the transition between the adiabatic inspirai and the plunge, and which provides a first estimate of the gravitational waveform emitted during the late dynamical evolution of a binary black-hole system.

Detecting large-scale deviations from a FRW geometry with future CMB observations

Abstract: We discuss the question to what degree the geometrical structure and the matter content of the universe at scales exceeding the present Hubble horizon is constrained by cosmological observations, in particular by measurements of the cosmic microwave background radiation. For an answer, a simple formalism is described, which goes back to a paper by Kristian and Sachs in 1966.

On Holography in Brans-Dicke Cosmology

Abstract: The holographic bound in Brans-Dicke $k=1$ matter dominated Cosmology is discussed In this talk, both the apparent horizon and the particle horizon are taken for the holographic bound The covariant entropy conjecture proposed by Bousso is also discussed