Particle horizon

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

Universe in the inflationary phase: Revisited

Abstract: The inflationary phase of the Universe is explored by proposing a toy model related to the scalar field, termed as `inflaton'. The potential part of the energy density in the said era is assumed to have a constant vacuum energy density part and a variable part containing the inflaton. The prime idea of the proposed model constructed in the framework of the closed universe is based on a fact that the inflaton is the root cause of the orientation of the space. According to this model the expansion of the Universe in the inflationary epoch is not approximately rather exactly exponential in nature and thus it can solve some of the fundamental puzzles, viz. flatness and horizon problems. The model keeps room for the end of inflationary era.

Holographic Description of the Early Universe

Abstract: The holographic principle is applied to a description of the Universe in the early stage of its evolution. As an example, we examine a cosmological model with a bounce with subsequent transition to the early stage of inflation. We investigate cosmological models based on a viscous liquid with a generalized equation of state in terms of the holographic cutoff proposed by Nojiri and Odintsov. Within the framework of these models, we have calculated the infrared radius in terms of the particle horizon or the event horizon. Energy conservation laws are obtained from the holographic point of view. The viscous liquid describing the bounce and the early Universe is presented as a generalization of holographic energy.

Five-dimensional bulk with a time-dependent warp factor and its consequences on brane cosmology

Abstract: In this paper, we have considered a 5-dimensional warped product space-time with a timedependent warp factor. The time-dependent warp factor plays an important role in localizing matter to the 4-dimensional hypersurface constituting the observed universe. We then proceed to determine the nature of modifications produced in the bulk geometry as well as the consequences on the corresponding braneworld. The five-dimensional field equations are constructed. For the bulk metric chosen, the Weyl tensor is found to vanish under a certain condition, thereby satisfying the conditions of a constant curvature bulk. Consequently we have constructed the solutions to the field equations for such a bulk and have studied its physical properties. The braneworld is described by a flat FRW-type metric in the ordinary spatial dimension. It is found that the the effective cosmological constant for the induced matter is a variable quantity monitored by the time-dependent warp factor and is associated with the bending of the braneworlds. The universe is initially decelerated, but subsequently makes a transition to an accelerated phase at later times, when its dynamics is dominated by the dynamical dark energy component. For a particular choice of the warp factor, it has been found that the universe is represented by a model of dark energy with the age of the universe as the measure of length, driving the universe to a state of accelerated expansion at later times.

Edge of the Universe: A Voyage to the Cosmic Horizon and Beyond

Abstract: Prologue: Cosmology's Extraordinary New Frontiers 1 1 How Far Out Can We See?: Voyage to the Edge of the Known Universe 7 2 How Was the Universe Born?: Revealing the Dawn of Time 22 3 How Far Away Will the Edge Get?: The Discovery of the Accelerating Universe 39 4 Why Does the Universe Seem So Smooth?: The Inflationary Era 52 5 What Is Dark Energy?: Will It Tear Space Apart? 67 6 Do We Live in a Hologram?: Exploring the Boundaries of Information 82 7 Are There Alternatives to Inflation?: Extra Dimensions and the Big Bounce 96 8 What Builds Structure in the Universe?: The Search for Dark Matter 110 9 What Is Tugging on Galaxies?: The Mysteries of Dark Flow and the Great Attractor 125 10 What Is the "Axis of Evil"?: Investigating Strange Features of the Cosmic Background 137 11 What Are the Immense Blasts of Energy from the Farthest Reaches of Space?: Gamma-Ray Bursts and the Quest for Cosmic Dragons 148 12 Can We Journey to Parallel Universes?: Wormholes as Gateways 161 13 Is The Universe Constantly Splitting into Multiple Realities?: The Many-Worlds Hypothesis 174 14 How Will the Universe End?: With a Bang, Bounce, Crunch, Rip, Stretch, or Whimper? 188 15 What Are the Ultimate Limits of Our Knowledge about the Cosmos? 204 Acknowledgments 217 Notes 219 Further Reading 225 Index 229

The fractal bubble model with a cosmological constant

Abstract: We generalize the fractal bubble model (FB), recently proposed in the literature as an alternative to the standard $\Lambda$CDM cosmology, to include a non-zero cosmological constant. We retain the same volume partition of voids and walls as the original FB model, and the same matching conditions for null geodesics, but do not include effects associated with a nonuniform time flow arising from differences of quasilocal gravitational energy that may arise in the coarse-graining process. The Buchert equations are written and partially integrated and the asymptotic behaviour of the solutions is given. For a universe with $\Lambda=0$, as it is the case in the FB model, an initial void fraction with hyperbolic curvature evolves in such a way that it asymptotically fills completely our particle horizon. Conversely, in presence of a non vanishing $\Lambda$, we show that this does not happen and the voids fill a finite fraction $f_{v_{\infty}}<1$, where the value of $(1-f_{v_{\infty}})$ is expected to depend on $\Lambda$ and the initial fraction $f_{vi}$ and also to be small. For its determination, a numerical integration of the equations is necessary. Finally, an interesting prediction of our model is a formula giving a minimum allowed value of present day dark energy as a function of the age of the universe and of the matter and curvature density parameters at our time.