Related papers: Initial Conditions in Pre-Big Bang
We investigate the initial conditions problem for multifield inflation. In these scenarios the pre-inflationary dynamics can be chaotic, increasing the sensitivity of the onset of inflation to the initial data even in the homogeneous limit.…
We study the entire coupled evolution of the inflaton and the scale factor for general initial conditions at a given initial time. The generic early universe evolution has three stages: decelerated fast-roll followed by inflationary fast…
In the standard hot big bang model, the expansion of the early universe is given by the Friedmann equation with an energy density dominated by relativistic particles. Since in a variety of models this equation is altered, we introduce…
After a brief summary of general relativity and cosmology, we present the basic concepts underlying inflation, the currently best motivated models for the early Universe. We describe the simplest inflation models, based on a single scalar…
In pre-big-bang string cosmology one uses a phase of dilaton-driven inflation to stretch an initial (microscopic) spatial patch to the (much larger) size of the big-bang fireball. We show that the dilaton-driven inflationary phase does not…
Over the past three years we have determined the basic features of our Universe. It is spatially flat; accelerating; comprised of 1/3 a new form of matter, 2/3 a new form of energy, with some ordinary matter and a dash of massive neutrinos;…
The different couplings of the dilaton to the U(1) gauge field of heterotic and Type I superstrings may leave an imprint on the relics of the very early cosmological evolution. Working in the context of the pre-big bang scenario, we discuss…
An introductory account is given of the modern understanding of the physics of the early Universe. Particular emphasis is placed on the paradigm of cosmological inflation, which postulates a period of accelerated expansion during the…
A variety of supergravity and string models involve hidden sectors where the hidden sectors may couple feebly with the visible sectors via a variety of portals. While the coupling of the hidden sector to the visible sector is feeble its…
Within the framework of an eternal inflationary scenario, a natural question regarding the production of eternal bubbles is the essential condition requires to have a universe capable of generating life. In either an open or a closed…
Though predictions of the simplest inflationary cosmological models with cold dark matter, flat space and approximately flat initial spectrum of adiabatic perturbations are remarkably close to observational data, we have to go beyond them…
There is an apparent power deficit relative to the Lambda-CDM prediction of the CMB spectrum at large scales, which, though not yet statistically significant, persists from WMAP to Planck data. We first present a simple toy model…
We analyze the quantum cosmology of the simplest pre--big--bang model without dilaton potential. In addition to the minisuperspace variables we include inhomogeneous dilaton fluctuations and determine their wave function on a semiclassical…
The inflationary scenario is not the only paradigm of early universe cosmology which is consistent with current observations. General criteria will be presented which any successful early universe model must satisfy. Various ways, including…
We point out that the horizon problem encountered in standard text-books or review papers on cosmology is, in general, derived for world models based on Robertson-Walker line element where homogeneity and isotropy of the universe -- \`a la…
In the standard big bang model the universe starts in a radiation dominated era, where the gravitational perturbations are described by second order differential equations, which will generally have two orthogonal set of solutions. One is…
The Big Bang singularity in standard model cosmology suggests a program of study in 'early universe' quantum gravity phenomenology. Inflation is usually thought to undermine this program's prospects by means of a dynamical diluting…
Using Bogomil'nyi inequality and the vanishing of topological charge at the unset of nucleation of a new universe permits a simpler,more direct insight into how topological defects (kinks and anti kinks) contribute to initial conditions at…
While cosmological inflation can erase primordial inhomogeneities, it is possible that inflation may not begin in a significantly inhomogeneous universe. This issue is particularly pressing in multifield scenarios, where even the…
The primordial bispectrum has been considered in the past decade as a powerful probe of the physical processes taking place in the early Universe. Within the inflationary paradigm, the properties of the bispectrum are one of the keys that…