9,089 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.
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.
A parametrization of the growth index of matter perturbations in various Dark Energy models and observational prospects using a Euclid-like survey
We provide exact solutions to the cosmological matter perturbation equation
in a homogeneous FLRW universe with a vacuum energy that can be parametrized by
a constant equation of state parameter and a very accurate approximation
for the Ansatz . We compute the growth index \gamma=\log
f(a)/\log\Om_m(a), and its redshift dependence, using the exact and
approximate solutions in terms of Legendre polynomials and show that it can be
parametrized as in most cases. We then
compare four different types of dark energy (DE) models: CDM, DGP,
and a LTB-large-void model, which have very different behaviors at
z\gsim1. This allows us to study the possibility to differentiate between
different DE alternatives using wide and deep surveys like Euclid, which will
measure both photometric and spectroscopic redshifts for several hundreds of
millions of galaxies up to redshift . We do a Fisher matrix analysis
for the prospects of differentiating among the different DE models in terms of
the growth index, taken as a given function of redshift or with a principal
component analysis, with a value for each redshift bin for a Euclid-like
survey. We use as observables the complete and marginalized power spectrum of
galaxies and the Weak Lensing (WL) power spectrum. We find that, using
, one can reach (2%, 5%) errors in , and (4%, 12%) errors in
, while using WL we get errors at least twice as large.
These estimates allow us to differentiate easily between DGP, models and
CDM, while it would be more difficult to distinguish the latter from a
variable equation of state parameter or LTB models using only the growth
index.}Comment: 29 pages, 7 figures, 6 table
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
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
The iron deposit of Cerro Huacravilca, Junin
En el cerro Huacravilca se encuentran concentraciones de magnetita, de forma aproximadamente tabular, en zonas a lo largo del contacto entre el stock del cerro Huacravilca y la caliza triásica adyacente. Las rocas ígneas del stock, monzonita cuarcífera o granodiorita, y la caliza están fuertemente alteradas cerca del contacto. La monzonita cuarcífera ha sido reemplazada por ortosa, granate y epidota. La caliza se ha convertido en tactita constituida principalmente por granate, diopsida y magnetita y, en menor cantidad, una serie de silicatos y sulfuros. Generalmente los cuerpos de magnetita contienen bastantes impurezas, mayormente silicatos. Las masas de magnetita esencialmente pura y de tamaño regular no son muy abundantes. La mena común consiste de láminas alternadas de magnetita y caliza alterada. La oxidación es mayormente superficial, aunque también se encuentra hematita a mayores profundidades. Es probable que ninguno de los cuerpos contenga más de unos cuantos millones de toneladas de magnetita y además la extracción selectiva de gran parte de esta mena sería muy difícil. Las posibilidades económicas del yacimiento son muy limitadas debido a la baja ley de la mena, el pequeño tonelaje probable y la distancia a los centros de consumo
Fluorescence and Hybrid Detection Aperture of the Pierre Auger Observatory
The aperture of the Fluorescence Detector (FD) of the Pierre Auger
Observatory is evaluated from simulated events using different detector
configurations: mono, stereo, 3-FD and 4-FD. The trigger efficiency has been
modeled using shower profiles with ground impacts in the field of view of a
single telescope and studying the trigger response (at the different levels) by
that telescope and by its neighbours. In addition, analysis cuts imposed by
event reconstruction have been applied. The hybrid aperture is then derived for
the Auger final extension. Taking into account the actual Surface Detector (SD)
array configuration and its trigger response, the aperture is also calculated
for a typical configuration of the present phase.Comment: contribution to the 29th International Cosmic Ray Conference, Pune,
India, 3-10 August 200
Supernovae as seen by off-center observers in a local void
Inhomogeneous universe models have been proposed as an alternative
explanation for the apparent acceleration of the cosmic expansion that does not
require dark energy. In the simplest class of inhomogeneous models, we live
within a large, spherically symmetric void. Several studies have shown that
such a model can be made consistent with many observations, in particular the
redshift--luminosity distance relation for type Ia supernovae, provided that
the void is of Gpc size and that we live close to the center. Such a scenario
challenges the Copernican principle that we do not occupy a special place in
the universe. We use the first-year Sloan Digital Sky Survey-II supernova
search data set as well as the Constitution supernova data set to put
constraints on the observer position in void models, using the fact that
off-center observers will observe an anisotropic universe. We first show that a
spherically symmetric void can give good fits to the supernova data for an
on-center observer, but that the two data sets prefer very different voids. We
then continue to show that the observer can be displaced at least fifteen
percent of the void scale radius from the center and still give an acceptable
fit to the supernova data. When combined with the observed dipole anisotropy of
the cosmic microwave background however, we find that the data compells the
observer to be located within about one percent of the void scale radius. Based
on these results, we conclude that considerable fine-tuning of our position
within the void is needed to fit the supernova data, strongly disfavouring the
model from a Copernican principle point of view.Comment: 20 pages, 6 figures, matches the published versio
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