16,370 research outputs found
Dual interacting cosmologies and late accelerated expansion
In this paper we show that by considering a universe dominated by two
interacting components a superaccelerated expansion can be obtained from a
decelerated one by applying a dual transformation that leaves the Einstein's
field equations invariant.Comment: 13 pages, 1 figura, version to match published articl
Constraints on Cold Dark Matter Accelerating Cosmologies and Cluster Formation
We discuss the properties of homogeneous and isotropic flat cosmologies in
which the present accelerating stage is powered only by the gravitationally
induced creation of cold dark matter (CCDM) particles (). For
some matter creation rates proposed in the literature, we show that the main
cosmological functions such as the scale factor of the universe, the Hubble
expansion rate, the growth factor and the cluster formation rate are
analytically defined. The best CCDM scenario has only one free parameter and
our joint analysis involving BAO + CMB + SNe Ia data yields
() where
is the observed matter density parameter. In particular, this implies that the
model has no dark energy but the part of the matter that is effectively
clustering is in good agreement with the latest determinations from large scale
structure. The growth of perturbation and the formation of galaxy clusters in
such scenarios are also investigated. Despite the fact that both scenarios may
share the same Hubble expansion, we find that matter creation cosmologies
predict stronger small scale dynamics which implies a faster growth rate of
perturbations with respect to the usual CDM cosmology. Such results
point to the possibility of a crucial observational test confronting CCDM with
CDM scenarios trough a more detailed analysis involving CMB, weak
lensing, as well as the large scale structure.Comment: 12 pages, 3 figures, Accepted for publication by Physical Rev.
New Cosmic Accelerating Scenario without Dark Energy
We propose an alternative, nonsingular, cosmic scenario based on
gravitationally induced particle production. The model is an attempt to evade
the coincidence and cosmological constant problems of the standard model
(CDM) and also to connect the early and late time accelerating stages
of the Universe. Our space-time emerges from a pure initial de Sitter stage
thereby providing a natural solution to the horizon problem. Subsequently, due
to an instability provoked by the production of massless particles, the
Universe evolves smoothly to the standard radiation dominated era thereby
ending the production of radiation as required by the conformal invariance.
Next, the radiation becomes sub-dominant with the Universe entering in the cold
dark matter dominated era. Finally, the negative pressure associated with the
creation of cold dark matter (CCDM model) particles accelerates the expansion
and drives the Universe to a final de Sitter stage. The late time cosmic
expansion history of the CCDM model is exactly like in the standard
CDM model, however, there is no dark energy. This complete scenario is
fully determined by two extreme energy densities, or equivalently, the
associated de Sitter Hubble scales connected by , a result that has no correlation with the cosmological constant
problem. We also study the linear growth of matter perturbations at the final
accelerating stage. It is found that the CCDM growth index can be written as a
function of the growth index, . In this
framework, we also compare the observed growth rate of clustering with that
predicted by the current CCDM model. Performing a statistical test
we show that the CCDM model provides growth rates that match sufficiently well
with the observed growth rate of structure.Comment: 12 pages, 3 figures, accepted for publication by Phys. Rev. D. (final
version, some references have corrected). arXiv admin note: substantial text
overlap with arXiv:1106.193
Monitoramento, sanitização e controle químico no manejo da mancha de corinespora do mamoeiro.
bitstream/item/80202/1/Mancha-de-CorynesporadoMamoeiro69.pd
Influence of temperature and storage time on anthocyanin stability of grape juice treated by hot filling.
The objective of this study was to analyze the storage temperatures on anthocyanins content of grape juices bottled hot, simulating inadequate cooling and storage conditions
Classical and quantum dynamics of confined test particles in brane gravity
A model is constructed for the confinement of test particles moving on a
brane. Within the classical framework of this theory, confining a test particle
to the brane eliminates the effects of extra dimensions, rendering them
undetectable. However, in the quantized version of the theory, the effects of
the gauge fields and extrinsic curvature are pronounced and this might provide
a hint for detecting them. As a consequence of confinement the mass of the test
particle is shown to be quantized. The condition of stability against small
perturbations along extra dimensions is also studied and its relation to dark
matter is discussed.Comment: 15 pages, no figures, extended, references adde
Observational constraints on interacting quintessence models
We determine the range of parameter space of Interacting Quintessence Models
that best fits the recent WMAP measurements of Cosmic Microwave Background
temperature anisotropies. We only consider cosmological models with zero
spatial curvature. We show that if the quintessence scalar field decays into
cold dark matter at a rate that brings the ratio of matter to dark energy
constant at late times,the cosmological parameters required to fit the CMB data
are: \Omega_x = 0.43 \pm 0.12, baryon fraction \Omega_b = 0.08 \pm 0.01, slope
of the matter power spectrum at large scals n_s = 0.98 \pm 0.02 and Hubble
constant H_0 = 56 \pm 4 km/s/Mpc. The data prefers a dark energy component with
a dimensionless decay parameter c^2 =0.005 and non-interacting models are
consistent with the data only at the 99% confidence level. Using the Bayesian
Information Criteria we show that this exra parameter fits the data better than
models with no interaction. The quintessence equation of state parameter is
less constrained; i.e., the data set an upper limit w_x \leq -0.86 at the same
level of significance. When the WMAP anisotropy data are combined with
supernovae data, the density parameter of dark energy increases to \Omega_x
\simeq 0.68 while c^2 augments to 6.3 \times 10^{-3}. Models with quintessence
decaying into dark matter provide a clean explanation for the coincidence
problem and are a viable cosmological model, compatible with observations of
the CMB, with testable predictions. Accurate measurements of baryon fraction
and/or of matter density independent of the CMB data, would support/disprove
these models.Comment: 16 pages, Revtex4, 5 eps figures, to appear in Physical Review
Bound vortex states and exotic lattices in multi-component Bose-Einstein condensates: The role of vortex-vortex interaction
We numerically study the vortex-vortex interaction in multi-component
homogeneous Bose-Einstein condensates within the realm of the Gross-Pitaevskii
theory. We provide strong evidences that pairwise vortex interaction captures
the underlying mechanisms which determine the geometric configuration of the
vortices, such as different lattices in many-vortex states, as well as the
bound vortex states with two (dimer) or three (trimer) vortices. Specifically,
we discuss and apply our theoretical approach to investigate intra- and
inter-component vortex-vortex interactions in two- and three-component
Bose-Einstein condensates, thereby shedding light on the formation of the
exotic vortex configurations. These results correlate with current experimental
efforts in multi-component Bose-Einstein condensates, and the understanding of
the role of vortex interactions in multiband superconductors.Comment: Published in PR
Complementary Constraints on Brane Cosmology
The acceleration of the expansion of the universe represents one of the major
challenges to our current understanding of fundamental physics. In principle,
to explain this phenomenon, at least two different routes may be followed:
either adjusting the energy content of the Universe -- by introducing a
negative-pressure dark energy -- or modifying gravity at very large scales --
by introducing new spatial dimensions, an idea also required by unification
theories. In the cosmological context, the role of such extra dimensions as the
source of the dark pressure responsable for the acceleration of our Universe is
translated into the so-called brane world (BW) cosmologies. Here we study
complementary constraints on a particular class of BW scenarios in which the
modification of gravity arises due to a gravitational \emph{leakage} into extra
dimensions. To this end, we use the most recent Chandra measurements of the
X-ray gas mass fraction in galaxy clusters, the WMAP determinations of the
baryon density parameter, measurements of the Hubble parameter from the
\emph{HST}, and the current supernova data. In agreement with other recent
results, it is shown that these models provide a good description for these
complementary data, although a closed scenario is always favored in the joint
analysis. We emphasize that observational tests of BW scenarios constitute a
natural verification of the role of possible extra dimensions in both
fundamental physics and cosmology.Comment: 6 Pages, 4 Figures, LaTe
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