9,715 research outputs found
Pair Creation of Dilaton Black Holes in Extended Inflation
Dilatonic Charged Nariai instantons mediate the nucleation of black hole
pairs during extended chaotic inflation. Depending on the dilaton and inflaton
fields, the black holes are described by one of two approximations in the
Lorentzian regime. For each case we find Euclidean solutions that satisfy the
no boundary proposal. The complex initial values of the dilaton and inflaton
are determined, and the pair creation rate is calculated from the Euclidean
action. Similar to standard inflation, black holes are abundantly produced near
the Planck boundary, but highly suppressed later on. An unusual feature we find
is that the earlier in inflation that the dilatonic black holes are created,
the more highly charged they can be.Comment: 23 pages, LaTeX, 6 figures; submitted to Phys. Rev.
Metric perturbations in two-field inflation
We study the metric perturbations produced during inflation in models with
two scalar fields evolving simultaneously. In particular, we emphasize how the
large-scale curvature perturbation on fixed energy density
hypersurfaces may not be conserved in general for multiple field inflation due
to the presence of entropy as well as adiabatic fluctuations. We show that the
usual method of solving the linearized perturbation equations is equivalent to
the recently proposed analysis of Sasaki and Stewart in terms of the perturbed
expansion along neighboring trajectories in field-space. In the case of a
separable potential it is possible to compute in the slow-roll approximation
the spectrum of density perturbations and gravitational waves at the end of
inflation. In general there is an inequality between the ratio of tensor to
scalar perturbations and the tilt of the gravitational wave spectrum, which
becomes an equality when only adiabatic perturbations are possible and
is conserved.Comment: RevTex, 9 pages, 1 uuencoded figure appended, also available on WWW
via http://star.maps.susx.ac.uk/index.htm
Uncertainties of predictions in models of eternal inflation
In a previous paper \cite{MakingPredictions}, a method of comparing the
volumes of thermalized regions in eternally inflating universe was introduced.
In this paper, we investigate the dependence of the results obtained through
that method on the choice of the time variable and factor ordering in the
diffusion equation that describes the evolution of eternally inflating
universes. It is shown, both analytically and numerically, that the variation
of the results due to factor ordering ambiguity inherent in the model is of the
same order as their variation due to the choice of the time variable.
Therefore, the results are, within their accuracy, free of the spurious
dependence on the time parametrization.Comment: 30 pages, RevTeX, figure included, added some references and Comments
on recent proposal (gr-qc/9511058) of alternative regularization schemes, to
appear in Phys. Rev.
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
Measuring the transition to homogeneity with photometric redshift surveys
We study the possibility of detecting the transition to homogeneity using
photometric redshift catalogs. Our method is based on measuring the fractality
of the projected galaxy distribution, using angular distances, and relies only
on observable quantites. It thus provides a way to test the Cosmological
Principle in a model-independent unbiased way. We have tested our method on
different synthetic inhomogeneous catalogs, and shown that it is capable of
discriminating some fractal models with relatively large fractal dimensions, in
spite of the loss of information due to the radial projection. We have also
studied the influence of the redshift bin width, photometric redshift errors,
bias, non-linear clustering, and surveyed area, on the angular homogeneity
index H2 ({\theta}) in a {\Lambda}CDM cosmology. The level to which an upcoming
galaxy survey will be able to constrain the transition to homogeneity will
depend mainly on the total surveyed area and the compactness of the surveyed
region. In particular, a Dark Energy Survey (DES)-like survey should be able to
easily discriminate certain fractal models with fractal dimensions as large as
D2 = 2.95. We believe that this method will have relevant applications for
upcoming large photometric redshift surveys, such as DES or the Large Synoptic
Survey Telescope (LSST).Comment: 14 pages, 14 figure
Non-equilibrium Goldstone phenomenon in tachyonic preheating
The dominance of the direct production of elementary Goldstone waves is
demonstrated in tachyonic preheating by numerically determining the evolution
of the dispersion relation, the equation of state and the kinetic power spectra
for the angular degree of freedom of the complex matter field. The importance
of the domain structure in the order parameter distribution for the
quantitative understanding of the excitation mechanism is emphasized. Evidence
is presented for the very early decoupling of the low-momentum Goldstone modes.Comment: 14 LaTeX pages, 5 figures, version published in Phys. Rev.
Microwave background anisotropies in quasiopen inflation
Quasiopenness seems to be generic to multi-field models of single-bubble open
inflation. Instead of producing infinite open universes, these models actually
produce an ensemble of very large but finite inflating islands. In this paper
we study the possible constraints from CMB anisotropies on existing models of
open inflation. The effect of supercurvature anisotropies combined with the
quasiopenness of the inflating regions make some models incompatible with
observations, and severely reduces the parameter space of others. Supernatural
open inflation and the uncoupled two-field model seem to be ruled out due to
these constraints for values of . Others, such as the
open hybrid inflation model with suitable parameters for the slow roll
potential can be made compatible with observations.Comment: 19 pages, ReVTeX, 10 figures inserted with eps
Complete power spectrum for an induced gravity open inflation model
We study the phenomenological constraints on a recently proposed model of
open inflation in the context of induced gravity. The main interest of this
model is the relatively small number of parameters, which may be constrained by
many different types of observation. We evaluate the complete spectrum of
density perturbations, which contains continuum sub-curvature modes, a discrete
super curvature mode, and a mode associated with fluctuations in the bubble
wall. From these, we compute the angular power spectrum of temperature
fluctuations in the microwave background, and derive bounds on the parameters
of the model so that the predicted spectrum is compatible with the observed
anisotropy of the microwave background and with large-scale structure
observations. We analyze the matter era and the approach of the model to
general relativity. The model passes all existing constraints.Comment: 12 pages RevTeX file with four figures incorporated (uses RevTeX and
epsf). Also available by e-mailing ARL, or by WWW at
http://star-www.maps.susx.ac.uk/papers/early_papers.html Only change is
additional reference
Preheating in Hybrid Inflation
We investigate a possibility of preheating in hybrid inflation. This scenario involves at least two scalar fields, the inflaton field , and the symmetry breaking field . We found that the behavior of these fields after inflation, as well as the possibility of preheating, depends crucially on the ratio of the coupling constant (self-interaction of the field For , oscillations of the field soon after inflation become very small, and all energy is concentrated in the oscillating field light scalar (or vector) fields~. For both fields motion stabilizes, and parametric resonance with production of particles becomes possible. For parametric resonance typically does not occur, though some exceptions from this rule are possible. In the recently proposed hybrid models with a second stage of inflation after the phase transition, both preheating and usual reheating are inefficient. Therefore for a very long time the universe remains in a state with vanishing pressure. As a result, density contrasts generated during the phase transition in these models can grow and collapse to form primordial black holes. Under certain conditions, most of the energy density after inflation will be stored in small black holes, which will later evaporate and reheat the universe
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