8,292 research outputs found
A Toy Model for Open Inflation
The open inflation scenario based on the theory of bubble formation in the
models of a single scalar field suffered from a fatal defect. In all the
versions of this scenario known so far, the Coleman-De Luccia instantons
describing the creation of an open universe did not exist. We propose a simple
one-field model where the CDL instanton does exist and the open inflation
scenario can be realized.Comment: 7 pages, 4 figures, revtex, a discussion of density perturbations is
extende
Towards a gauge invariant volume-weighted probability measure for eternal inflation
An improved volume-weighted probability measure for eternal inflation is
proposed. For the models studied in this paper it leads to simple and
intuitively expected gauge-invariant results.Comment: 16 pages, 3 figs, few misprints corrected, comments adde
False Vacuum Chaotic Inflation: The New Paradigm?
Recent work is reported on inflation model building in the context of
supergravity and superstrings, with special emphasis on False Vacuum (`Hybrid')
Chaotic Inflation. Globally supersymmetric models do not survive in generic
supergravity theories, but fairly simple conditions can be formulated which do
ensure successful supergravity inflation. The conditions are met in some of the
versions of supergravity that emerge from superstrings.Comment: 4 pages, LATEX, LANCASTER-TH 94-1
Study of the Coleman - de Luccia instanton of the second order
We study the second order Coleman - de Luccia instanton which appears as the
curvature of the effective potential reaches a sufficiently large value. We
show how one can find the approximative formula for this instanton by
perturbative expansion in the case when the second derivative of the effective
potential divided by the Hubble parameter squared is close to -10, and we
perform a numerical study of this instanton in the case of quasi-exponential
potential.Comment: three pages, one figur
Unambiguous probabilities in an eternally inflating universe
``Constants of Nature'' and cosmological parameters may in fact be variables
related to some slowly-varying fields. In models of eternal inflation, such
fields will take different values in different parts of the universe. Here I
show how one can assign probabilities to values of the ``constants'' measured
by a typical observer. This method does not suffer from ambiguities previously
discussed in the literature.Comment: 7 pages, Final version (minor changes), to appear in Phys. Rev. Let
Isocurvature bounds on axions revisited
The axion is one of the best motivated candidates for particle dark matter.
We study and update the constraints imposed by the recent CMB and LSS
experiments on the mass of axions produced by the misalignment mechanism, as a
function of both the inflationary scale and the reheating temperature. Under
some particular although not unconventional assumptions, the axionic field
induces too large isocurvature perturbations. Specifically, for inflation
taking place at intermediate energy scales, we derive some restrictive limits
which can only be evaded by assuming an efficient reheating mechanism, with
T>10^{11} GeV. Chaotic inflation with a quadratic potential is still compatible
with the axion scenario, provided that the Peccei-Quinn scale f_a is close to
10^{10} or 10^{11} GeV. Isocurvature bounds eliminate the possibility of a
larger f_a and a small misalignment angle. We find that isocurvature
constraints on the axion scenario must be taken into account whenever the scale
of inflation is above 10^{12} GeV; below this scale, axionic isocurvature modes
are too small to be probed by current observations.Comment: 12 pages, 3 figures; more concise version, new figures, accepted in
PR
Predictability crisis in inflationary cosmology and its resolution
Models of inflationary cosmology can lead to variation of observable
parameters ("constants of Nature") on extremely large scales. The question of
making probabilistic predictions for today's observables in such models has
been investigated in the literature. Because of the infinite thermalized volume
resulting from eternal inflation, it has proven difficult to obtain a
meaningful and unambiguous probability distribution for observables, in
particular due to the gauge dependence. In the present paper, we further
develop the gauge-invariant procedure proposed in a previous work for models
with a continuous variation of "constants". The recipe uses an unbiased
selection of a connected piece of the thermalized volume as sample for the
probability distribution. To implement the procedure numerically, we develop
two methods applicable to a reasonably wide class of models: one based on the
Fokker-Planck equation of stochastic inflation, and the other based on direct
simulation of inflationary spacetime. We present and compare results obtained
using these methods.Comment: 23 pages, 13 figure
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
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
Dynamical renormalization group methods in theory of eternal inflation
Dynamics of eternal inflation on the landscape admits description in terms of
the Martin-Siggia-Rose (MSR) effective field theory that is in one-to-one
correspondence with vacuum dynamics equations. On those sectors of the
landscape, where transport properties of the probability measure for eternal
inflation are important, renormalization group fixed points of the MSR
effective action determine late time behavior of the probability measure. I
argue that these RG fixed points may be relevant for the solution of the gauge
invariance problem for eternal inflation.Comment: 11 pages; invited mini-review for Grav.Cos
- …