11,542 research outputs found

### Restoring Time Dependence into Quantum Cosmology

Mini superspace cosmology treats the scale factor $a(t)$, the lapse function
$n(t)$, and an optional dilation field $\phi(t)$ as canonical variables. While
pre-fixing $n(t)$ means losing the Hamiltonian constraint, pre-fixing $a(t)$ is
serendipitously harmless at this level. This suggests an alternative to the
Hartle-Hawking approach, where the pre-fixed $a(t)$ and its derivatives are
treated as explicit functions of time, leaving $n(t)$ and a now mandatory
$\phi(t)$ to serve as canonical variables. The naive gauge pre-fix $a(t)=const$
is clearly forbidden, causing evolution to freeze altogether, so pre-fixing the
scale factor, say $a(t)=t$, necessarily introduces explicit time dependence
into the Lagrangian. Invoking Dirac's prescription for dealing with
constraints, we construct the corresponding mini superspace time dependent
total Hamiltonian, and calculate the Dirac brackets, characterized by
$\{n,\phi\}_D\neq 0$, which are promoted to commutation relations in the
quantum theory.Comment: Honorable Mentioned essay - Gravity Research Foundation 201

### Landscape Predictions from Cosmological Vacuum Selection

In BP models with hundreds of fluxes, we compute the effects of cosmological
dynamics on the probability distribution of landscape vacua. Starting from
generic initial conditions, we find that most fluxes are dynamically driven
into a different and much narrower range of values than expected from landscape
statistics alone. Hence, cosmological evolution will access only a tiny
fraction of the vacua with small cosmological constant. This leads to a host of
sharp predictions. Unlike other approaches to eternal inflation, the
holographic measure employed here does not lead to "staggering", an excessive
spread of probabilities that would doom the string landscape as a solution to
the cosmological constant problem.Comment: 15 pages, 6 figures, v4 prd format, minor editin

### 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

### 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

### End of multi-field inflation and the perturbation spectrum

We investigate the dynamics of inflation models driven by multiple, decoupled
scalar fields and calculate the Hubble parameter and the amplitude of the
lightest field at the end of inflation which may be responsible for
interesting, or possibly dangerous cosmological consequences after inflation.
The results are very simple and similar to those of the single field inflation,
mainly depend on the underlying spectrum of the masses. The mass distribution
is heavily constrained by the power spectrum of density perturbations P and the
spectral index n. The overall mass scale gives the amplitude of P, and n is
affected by the number of fields and the spacing between masses in the
distribution. The drop-out effect of the massive fields makes the perturbation
spectrum typically redder than the single field inflation spectrum. We
illustrate this using two different mass distributions.Comment: (v1) 16 pages, 5 figures, 3 tables; (v2) 17 pages, references added,
typos corrected; (v3) references added, typos corrected; (v4) 16 pages, typos
corrected, Table 1 expanded and Table 3 removed, Figs. 2 and 3 reduced, to
appear in Physical Review

### Stochastic inflation on the brane

Chaotic inflation on the brane is considered in the context of stochastic
inflation. It is found that there is a regime in which eternal inflation on the
brane takes place. The corresponding probability distributions are found in
certain cases. The stationary probability distribution over a comoving volume
and the creation probability of a de Sitter braneworld yield the same
exponential behaviour. Finally, nonperturbative effects are briefly discussed.Comment: 9 page

### 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

### Cosmological Higgs fields

We present a time-dependent solution to the coupled Einstein-Higgs equations
for general Higgs-type potentials in the context of flat FRW cosmological
models. Possible implications are discussed.Comment: 5 pages, no figures. Version to be published in Phys. Rev. Lett.
Changes: references and citations added; introduction partly modified;
expanded discussion of relations between parameters in the Higgs potentia

### Measure Problem for Eternal and Non-Eternal Inflation

We study various probability measures for eternal inflation by applying their
regularization prescriptions to models where inflation is not eternal. For
simplicity we work with a toy model describing inflation that can interpolate
between eternal and non-eternal inflation by continuous variation of a
parameter. We investigate whether the predictions of four different measures
(proper time, scale factor cutoff, stationary and causal {diamond}) change
continuously with the change of this parameter. We will show that {only} for
the stationary measure the predictions change continuously. For the proper-time
and the scale factor cutoff, the predictions are strongly discontinuous. For
the causal diamond measure, the predictions are continuous only if the stage of
the slow-roll inflation is sufficiently long.Comment: 9 pages, 4 figure

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