128 research outputs found
Stationarity of Inflation and Predictions of Quantum Cosmology
We describe several different regimes which are possible in inflationary
cosmology. The simplest one is inflation without self-reproduction of the
universe. In this scenario the universe is not stationary. The second regime,
which exists in a broad class of inflationary models, is eternal inflation with
the self-reproduction of inflationary domains. In this regime local properties
of domains with a given density and given values of fields do not depend on the
time when these domains were produced. The probability distribution to find a
domain with given properties in a self-reproducing universe may or may not be
stationary, depending on the choice of an inflationary model. We give examples
of models where each of these possibilities can be realized, and discuss some
implications of our results for quantum cosmology. In particular, we propose a
new mechanism which may help solving the cosmological constant problem.Comment: 30 pages, Stanford preprint SU-ITP-94-24, LaTe
Reheating in nonminimal derivative coupling model
We consider a model with nonminimal derivative coupling of inflaton to
gravity. The reheating process during rapid oscillation of the inflaton is
studied and the reheating temperature is obtained. Behaviors of the inflaton
and produced radiation in this era are discussed.Comment: 16 pages, 5 figures; discussions added; accepted by JCA
Topological Defects as Seeds for Eternal Inflation
We investigate the global structure of inflationary universe both by
analytical methods and by computer simulations of stochastic processes in the
early Universe. We show that the global structure of the universe depends
crucially on the mechanism of inflation. In the simplest models of chaotic
inflation the Universe looks like a sea of thermalized phase surrounding
permanently self-reproducing inflationary domains. In the theories where
inflation occurs near a local extremum of the effective potential corresponding
to a metastable state, the Universe looks like de Sitter space surrounding
islands of thermalized phase. A similar picture appears even if the state is unstable but the effective potential has a discrete symmetry . In this case the Universe becomes divided into domains containing
different phases. These domains will be separated from each other by domain
walls. However, unlike ordinary domain walls, these domain walls will inflate,
and their thickness will exponentially grow. In the theories with continuous
symmetries inflation generates exponentially expanding strings and monopoles
surrounded by thermalized phase. Inflating topological defects will be stable,
and they will unceasingly produce new inflating topological defects. This means
that topological defects may play a role of indestructible seeds for eternal
inflation.Comment: 21 pages, 17 figures (not included), Stanford University preprint
SU--ITP--94--
Relaxing the Cosmological Moduli Problem
Typically the moduli fields acquire mass m =C H in the early universe, which
shifts the position of the minimum of their effective potential and leads to an
excessively large energy density of the oscillating moduli fields at the later
stages of the evolution of the universe. This constitutes the cosmological
moduli problem, or Polonyi field problem. We show that the cosmological moduli
problem can be solved or at least significantly relaxed in the theories in
which C >> 1, as well as in some models with C << 1.Comment: 9 pages, 3 Postscript figure
Particle Production and Gravitino Abundance after Inflation
Thermal history after inflation is studied in a chaotic inflation model with
supersymmetric couplings of the inflaton to matter fields. Time evolution
equation is solved in a formalism that incorporates both the back reaction of
particle production and the cosmological expansion. The effect of the
parametric resonance gives rise to a rapid initial phase of the inflaton decay
followed by a slow stage of the Born term decay. Thermalization takes place
immediately after the first explosive stage for a medium strength of the
coupling among created particles. As an application we calculate time evolution
of the gravitino abundance that is produced by ordinary particles directly
created from the inflaton decay, which typically results in much more enhanced
yield than what a naive estimate based on the Born term would suggest.Comment: 23 pages + 13 figure
Quantum Creation of an Open Inflationary Universe
We discuss a dramatic difference between the description of the quantum
creation of an open universe using the Hartle-Hawking wave function and the
tunneling wave function. Recently Hawking and Turok have found that the
Hartle-Hawking wave function leads to a universe with Omega = 0.01, which is
much smaller that the observed value of Omega > 0.3. Galaxies in such a
universe would be about light years away from each other, so the
universe would be practically structureless. We will argue that the
Hartle-Hawking wave function does not describe the probability of the universe
creation. If one uses the tunneling wave function for the description of
creation of the universe, then in most inflationary models the universe should
have Omega = 1, which agrees with the standard expectation that inflation makes
the universe flat. The same result can be obtained in the theory of a
self-reproducing inflationary universe, independently of the issue of initial
conditions. However, there exist two classes of models where Omega may take any
value, from Omega > 1 to Omega << 1.Comment: 23 pages, 4 figures. New materials are added. In particular, we show
that boundary terms do not help to solve the problem of unacceptably small
Omega in the new model proposed by Hawking and Turok in hep-th/9803156. A
possibility to solve the cosmological constant problem in this model using
the tunneling wave function is discusse
From the Big Bang Theory to the Theory of a Stationary Universe
We consider chaotic inflation in the theories with the effective potentials
phi^n and e^{\alpha\phi}. In such theories inflationary domains containing
sufficiently large and homogeneous scalar field \phi permanently produce new
inflationary domains of a similar type. We show that under certain conditions
this process of the self-reproduction of the Universe can be described by a
stationary distribution of probability, which means that the fraction of the
physical volume of the Universe in a state with given properties (with given
values of fields, with a given density of matter, etc.) does not depend on
time, both at the stage of inflation and after it. This represents a strong
deviation of inflationary cosmology from the standard Big Bang paradigm. We
compare our approach with other approaches to quantum cosmology, and illustrate
some of the general conclusions mentioned above with the results of a computer
simulation of stochastic processes in the inflationary Universe.Comment: No changes to the file, but original figures are included. They
substantially help to understand this paper, as well as eternal inflation in
general, and what is now called the "multiverse" and the "string theory
landscape." High quality figures can be found at
http://www.stanford.edu/~alinde/LLMbigfigs
Dark energy and key physical parameters of clusters of galaxies
We study physics of clusters of galaxies embedded in the cosmic dark energy
background. Under the assumption that dark energy is described by the
cosmological constant, we show that the dynamical effects of dark energy are
strong in clusters like the Virgo cluster. Specifically, the key physical
parameters of the dark mater halos in clusters are determined by dark energy:
1) the halo cut-off radius is practically, if not exactly, equal to the
zero-gravity radius at which the dark matter gravity is balanced by the dark
energy antigravity; 2) the halo averaged density is equal to two densities of
dark energy; 3) the halo edge (cut-off) density is the dark energy density with
a numerical factor of the unity order slightly depending on the halo profile.
The cluster gravitational potential well in which the particles of the dark
halo (as well as galaxies and intracluster plasma) move is strongly affected by
dark energy: the maximum of the potential is located at the zero-gravity radius
of the cluster.Comment: 8 pages, 1 figur
More on Tachyon Cosmology in De Sitter Gravity
We aim to study rolling tachyon cosmological solutions in de Sitter gravity.
The solutions are taken to be flat FRW type and these are not time-reversal
symmetric. We find that cosmological constant of our universe has to be
fine-tuned at the level of the action itself, as in KKLT string
compactification. The rolling tachyon can give rise to required inflation with
suitable choice of the initial conditions which include nonvanishing Hubble
constant. We also determine an upper bound on the volume of the
compactification manifold.Comment: 15pp, 3 figures; references adde
Equation of motion of a classical scalar field with back reaction of produced particles
In the one-loop approximation we derive the equation of motion for a
classical scalar field \phi_c (t) with the back reaction of particle production
included. Renormalization of mass and couplings of \phi_c is done explicitly.
The equation is non-local in time, but can easily be treated perturbatively or
numerically. For the weak trilinear coupling of the external field to the
produced particles, the new equation gives the same solution as the familiar
one with the \Gamma \phi_c term. For a stronger coupling and other types of
couplings the results are significantly different. The equation can be applied
to the universe heating by the inflaton decay and to spontaneous baryogenesis.Comment: 29 pages, 16 figures, subm to NP
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