5,847 research outputs found
Initial Conditions for Supersymmetric Inflation
We perform a numerical investigation of the fields evolution in the
supersymmetric inflationary model based on radiative corrections. Supergravity
corrections are also included. We find that, out of all the examined initial
data, only about 10% give an adequate amount of inflation and can be considered
as ''natural''. Moreover, these successful initial conditions appear scattered
and more or less isolated.Comment: 15 pages RevTeX 4 eps figure
Fine tuning of the initial conditions for hybrid inflation
We study the evolution of regions of space with various initial field values
for a simple theory that can support hybrid inflation. Only very narrow domains
within the range of initial field values below the Planck scale lead to the
onset of inflation. This implies a severe fine tuning for the initial
configuration that will produce inflation.Comment: 11 pages, LaTeX, 8 figures in eps forma
Thermodynamics via Creation from Nothing: Limiting the Cosmological Constant Landscape
The creation of a quantum Universe is described by a {\em density matrix}
which yields an ensemble of universes with the cosmological constant limited to
a bounded range . The
domain is ruled out by a cosmological bootstrap
requirement (the self-consistent back reaction of hot matter). The upper cutoff
results from the quantum effects of vacuum energy and the conformal anomaly
mediated by a special ghost-avoidance renormalization. The cutoff establishes a new quantum scale -- the accumulation point of an infinite
sequence of garland-type instantons. The dependence of the cosmological
constant range on particle phenomenology suggests a possible dynamical
selection mechanism for the landscape of string vacua.Comment: RevTex, 4 pages, 4 figure
Inflation with
We discuss various models of inflationary universe with . A
homogeneous universe with may appear due to creation of the
universe "from nothing" in the theories where the effective potential becomes
very steep at large , or in the theories where the inflaton field
nonminimally couples to gravity. Inflation with generally requires
intermediate first order phase transition with the bubble formation, and with a
second stage of inflation inside the bubble. It is possible to realize this
scenario in the context of a theory of one scalar field, but typically it
requires artificially bent effective potentials and/or nonminimal kinetic
terms. It is much easier to obtain an open universe in the models involving two
scalar fields. However, these models have their own specific problems. We
propose three different models of this type which can describe an open
homogeneous inflationary universe.Comment: 29 pages, LaTeX, parameters of one of the models are slightly
modifie
Pre-Big-Bang Requires the Universe to be Exponentially Large From the Very Beginning
We show that in a generic case of the pre-big-bang scenario, inflation will
solve cosmological problems only if the universe at the onset of inflation is
extremely large and homogeneous from the very beginning. The size of a
homogeneous part of the universe at the beginning of the stage of pre-big-bang
(PBB) inflation must be greater than , where is the
stringy length. The total mass of an inflationary domain must be greater than
, where . If the universe is initially
radiation dominated, then its total entropy at that time must be greater than
. If the universe is closed, then at the moment of its formation it
must be uniform over causally disconnected domains. The natural
duration of the PBB stage in this scenario is . We argue that the
initial state of the open PBB universe could not be homogeneous because of
quantum fluctuations. Independently of the issue of homogeneity, one must
introduce two large dimensionless parameters, , and , in order to solve the flatness problem in the PBB cosmology. A regime
of eternal inflation does not occur in the PBB scenario. This should be
compared with the simplest versions of the chaotic inflation scenario, where
the regime of eternal inflation may begin in a universe of size
with vanishing initial radiation entropy, mass , and geometric entropy
O(1). We conclude that the current version of the PBB scenario cannot replace
usual inflation even if one solves the graceful exit problem in this scenario.Comment: 14 pages, a discussion of the flatness problem in the PBB cosmology
is adde
Inflationary cosmology of the extreme cosmic string
Starting with a study of the cosmological solution to the Einstein equations
for the internal spacetime of an extreme supermassive cosmic string kink, and
by evaluating the probability measure for the formation of such a kink in
semiclassical approximation using a minisuperspace with the appropriate
symmetry, we have found a set of arguments in favor of the claim that the
kinked extreme string can actually be regarded as a unbounded chain of pairs of
Planck- sized universes. Once one such universe pairs is created along a
primordial phase transition at the Planck scale, it undergoes an endless
process of continuous self-regeneration driven by chaotic inflation in each of
the universes forming the pair.Comment: 15 pages, RevTex, to appear in Int. J. Mod. Phys.
Inflation without Slow Roll
We draw attention to the possibility that inflation (i.e. accelerated
expansion) might continue after the end of slow roll, during a period of fast
oscillations of the inflaton field \phi . This phenomenon takes place when a
mild non-convexity inequality is satisfied by the potential V(\phi). The
presence of such a period of \phi-oscillation-driven inflation can
substantially modify reheating scenarios.
In some models the effect of these fast oscillations might be imprinted on
the primordial perturbation spectrum at cosmological scales.Comment: 9 pages, Revtex, psfig, 1 figure, minor modifications, references
adde
Functional Approach to Stochastic Inflation
We propose functional approach to the stochastic inflationary universe
dynamics. It is based on path integral representation of the solution to the
differential equation for the scalar field probability distribution. In the
saddle-point approximation scalar field probability distributions of various
type are derived and the statistics of the inflationary-history-dependent
functionals is developed.Comment: 20 pages, Preprint BROWN-HET-960, uses phyzz
Supersymmetry breaking and loop corrections at the end of inflation
We show that quantum corrections to the effective potential in supersymmetric
hybrid inflation can be calculated all the way from the inflationary period -
when the Universe is dominated by a false vacuum energy density - till the
fields settle down to the global supersymmetric minimum of the potential. These
are crucial for getting a continuous description of the evolution of the
fields.Comment: minor corrections; version to be published in Phys. Rev.
Creation of a Compact Topologically Nontrivial Inflationary Universe
If inflation can occur only at the energy density V much smaller than the
Planck density, which is the case for many inflationary models based on string
theory, then the probability of quantum creation of a closed or an infinitely
large open inflationary universe is exponentially suppressed for all known
choices of the wave function of the universe. Meanwhile under certain
conditions there is no exponential suppression for creation of topologically
nontrivial compact flat or open inflationary universes. This suggests, contrary
to the standard textbook lore, that compact flat or open universes with
nontrivial topology should be considered a rule rather than an exception.Comment: 9 pages 2 figures, new materials and references adde
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