1,474 research outputs found
The Energy Density of "Wound" Fields in a Toroidal Universe
The observational limits on the present energy density of the Universe allow
for a component that redshifts like and can contribute significantly to
the total. We show that a possible origin for such a contribution is that the
universe has a toroidal topology with "wound" scalar fields around its cycles.Comment: 11 pages, 1figur
Scalar perturbation spectra from warm inflation
We present a numerical integration of the cosmological scalar perturbation
equations in warm inflation. The initial conditions are provided by a
discussion of the thermal fluctuations of an inflaton field and thermal
radiation using a combination of thermal field theory and thermodynamics. The
perturbation equations include the effects of a damping coefficient
and a thermodynamic potential . We give an analytic expression for the
spectral index of scalar fluctuations in terms of a new slow-roll parameter
constructed from . A series of toy models, inspired by spontaneous
symmetry breaking and a known form of the damping coefficient, lead to a
spectrum with on large scales and on small scales.Comment: 12 pages, 5 figures, RevTeX 4, revised with extra figure
Chemical similarity among domesticated and wild genotypes of peanut based on n-alkanes profiles
A new species of Djalmabatista Fittkau (Chironomidae, Tanypodinae) from Mato Grosso, Brazil
Caracterização fĂsico-quĂmica de frutos de novos hĂbridos e linhagens de mamoeiro
Lemaitre-Tolman-Bondi model and accelerating expansion
I discuss the spherically symmetric but inhomogeneous Lemaitre-Tolman- Bondi
(LTB) metric, which provides an exact toy model for an inhomogeneous universe.
Since we observe light rays from the past light cone, not the expansion of the
universe, spatial variation in matter density and Hubble rate can have the same
effect on redshift as acceleration in a perfectly homogeneous universe. As a
consequence, a simple spatial variation in the Hubble rate can account for the
distant supernova data in a dust universe without any dark energy. I also
review various attempts towards a semirealistic description of the universe
based on the LTB model.Comment: Invited Review for a special Gen. Rel. Grav. issue on Dark Energy. 17
pages, 3 figure
Assessment of antimicrobial activity in vitro of ethanolic extracts of Banisteriopsis anisandra (A. Juss.) B. Gates (Malpighiaceae)
Bianchi type I space and the stability of inflationary Friedmann-Robertson-Walker space
Stability analysis of the Bianchi type I universe in pure gravity theory is
studied in details. We first derive the non-redundant field equation of the
system by introducing the generalized Bianchi type I metric. This non-redundant
equation reduces to the Friedmann equation in the isotropic limit. It is shown
further that any unstable mode of the isotropic perturbation with respect to a
de Sitter background is also unstable with respect to anisotropic
perturbations. Implications to the choice of physical theories are discussed in
details in this paper.Comment: 5 pages, some comment adde
Observational Constraints on Chaplygin Quartessence: Background Results
We derive the constraints set by several experiments on the quartessence
Chaplygin model (QCM). In this scenario, a single fluid component drives the
Universe from a nonrelativistic matter-dominated phase to an accelerated
expansion phase behaving, first, like dark matter and in a more recent epoch
like dark energy. We consider current data from SNIa experiments, statistics of
gravitational lensing, FR IIb radio galaxies, and x-ray gas mass fraction in
galaxy clusters. We investigate the constraints from this data set on flat
Chaplygin quartessence cosmologies. The observables considered here are
dependent essentially on the background geometry, and not on the specific form
of the QCM fluctuations. We obtain the confidence region on the two parameters
of the model from a combined analysis of all the above tests. We find that the
best-fit occurs close to the CDM limit (). The standard
Chaplygin quartessence () is also allowed by the data, but only at
the level.Comment: Replaced to match the published version, references update
Double Inflation in Supergravity and the Large Scale Structure
The cosmological implication of a double inflation model with hybrid + new
inflations in supergravity is studied. The hybrid inflation drives an inflaton
for new inflation close to the origin through supergravity effects and new
inflation naturally occurs. If the total e-fold number of new inflation is
smaller than , both inflations produce cosmologically relevant density
fluctuations. Both cluster abundances and galaxy distributions provide strong
constraints on the parameters in the double inflation model assuming
standard cold dark matter scenario. The future satellite
experiments to measure the angular power spectrum of the cosmic microwave
background will make a precise determination of the model parameters possible.Comment: 19 pages (RevTeX file
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