135 research outputs found
Dark Energy and the quietness of the Local Hubble Flow
The linearity and quietness of the Local () Hubble Flow (LHF) in
view of the very clumpy local universe is a long standing puzzle in standard
and in open CDM cosmogony. The question addressed in this paper is whether the
antigravity component of the recently discovered dark energy can cool the
velocity flow enough to provide a solution to this puzzle. We calculate the
growth of matter fluctuations in a flat universe containing a fraction
of dark energy obeying the time independent equation of state
. We find that dark energy can indeed cool the LHF. However the
dark energy parameter values required to make the predicted velocity dispersion
consistent with the observed value have been ruled out
by other observational tests constraining the dark energy parameters and
. Therefore despite the claims of recent qualitative studies dark
energy with time independent equation of state can not by itself explain the
quietness and linearity of the Local Hubble Flow.Comment: 4 pages, 3 figures, accepted in Phys. Rev. D. Minor corrections, one
figure adde
The imprint of the interaction between dark sectors in galaxy clusters
Based on perturbation theory, we study the dynamics of how dark matter and
dark energy in the collapsing system approach dynamical equilibrium while
interacting. We find that the interaction between dark sectors cannot ensure
the dark energy to fully cluster along with dark, leading to the energy
non-conservation problem in the collapsing system We examine the cluster number
counts dependence on the interaction between dark sectors. Furthermore, we
analyze how dark energy inhomogeneities affect cluster abundances. It is shown
that cluster number counts can provide specific signature of dark sectors
interaction and dark energy inhomogeneities.Comment: revised version. New treatment has been provided on studying the
structure formation in the spherical collapsing system where DE does not
cluster together with DM. Accepted for publication in JCA
The imprint of the interaction between dark sectors in galaxy clusters
Based on perturbation theory, we study the dynamics of how dark matter and
dark energy in the collapsing system approach dynamical equilibrium while
interacting. We find that the interaction between dark sectors cannot ensure
the dark energy to fully cluster along with dark, leading to the energy
non-conservation problem in the collapsing system We examine the cluster number
counts dependence on the interaction between dark sectors. Furthermore, we
analyze how dark energy inhomogeneities affect cluster abundances. It is shown
that cluster number counts can provide specific signature of dark sectors
interaction and dark energy inhomogeneities.Comment: revised version. New treatment has been provided on studying the
structure formation in the spherical collapsing system where DE does not
cluster together with DM. Accepted for publication in JCA
Low-scale Quintessential Inflation
In quintessential inflationary model, the same master field that drives
inflation becomes, later on, the dynamical source of the (present) accelerated
expansion. Quintessential inflationary models require a curvature scale at the
end of inflation around in order to explain the large scale
fluctuations observed in the microwave sky. If the curvature scale at the end
of inflation is much smaller than , the large scale adiabatic
mode may be produced thanks to the relaxation of a scalar degree of freedom,
which will be generically denoted, according to the recent terminology, as the
curvaton field. The production of the adiabatic mode is analysed in detail in
the case of the minimal quintessential inflationary model originally proposed
by Peebles and Vilenkin.Comment: 25 pages; 5 figure
Perturbation evolution with a non-minimally coupled scalar field
We recently proposed a simple dilaton-derived quintessence model in which the
scalar field was non-minimally coupled to cold dark matter, but not to
`visible' matter. Such couplings can be attributed to the dilaton in the low
energy limit of string theory, beyond tree level. In this paper we discuss the
implications of such a model on structure formation, looking at its impact on
matter perturbations and CMB anisotropies. We find that the model only deviates
from CDM and minimally coupled theories at late times, and is well
fitted to current observational data. The signature left by the coupling, when
it breaks degeneracy at late times, presents a valuable opportunity to
constrain non-minimal couplings given the wealth of new observational data
promised in the near future.Comment: Version appearing in Physical Review D. 10 pages, 9 figs. Comparison
with SN1a and projected MAP results, and appendix adde
Gauge-ready formulation of the cosmological kinetic theory in generalized gravity theories
We present cosmological perturbations of kinetic components based on
relativistic Boltzmann equations in the context of generalized gravity
theories. Our general theory considers an arbitrary number of scalar fields
generally coupled with the gravity, an arbitrary number of mutually interacting
hydrodynamic fluids, and components described by the relativistic Boltzmann
equations like massive/massless collisionless particles and the photon with the
accompanying polarizations. We also include direct interactions among fluids
and fields. The background FLRW model includes the general spatial curvature
and the cosmological constant. We consider three different types of
perturbations, and all the scalar-type perturbation equations are arranged in a
gauge-ready form so that one can implement easily the convenient gauge
conditions depending on the situation. In the numerical calculation of the
Boltzmann equations we have implemented four different gauge conditions in a
gauge-ready manner where two of them are new. By comparing solutions solved
separately in different gauge conditions we can naturally check the numerical
accuracy.Comment: 26 pages, 9 figures, revised thoroughly, to appear in Phys. Rev.
Tension between SN and BAO: current status and future forecasts
Using real and synthetic Type Ia SNe (SNeIa) and baryon acoustic oscillations
(BAO) data representing current observations forecasts, this paper investigates
the tension between those probes in the dark energy equation of state (EoS)
reconstruction considering the well known CPL model and Wang's low correlation
reformulation. In particular, here we present simulations of BAO data from both
the the radial and transverse directions. We also explore the influence of
priors on Omega_m and Omega_b on the tension issue, by considering 1-sigma
deviations in either one or both of them. Our results indicate that for some
priors there is no tension between a single dataset (either SNeIa or BAO) and
their combination (SNeIa+BAO). Our criterion to discern the existence of
tension (sigma-distance) is also useful to establish which is the dataset with
most constraining power; in this respect SNeIa and BAO data switch roles when
current and future data are considered, as forecasts predict and spectacular
quality improvement on BAO data. We also find that the results on the tension
are blind to the way the CPL model is addressed: there is a perfect match
between the original formulation and that by the low correlation optimized, but
the errors on the parameters are much narrower in all cases of our exhaustive
exploration, thus serving the purpose of stressing the convenience of this
reparametrization.Comment: 21 pages, under review in JCA
Early-universe constraints on a Primordial Scaling Field
In the past years 'quintessence' models have been considered which can
produce the accelerated expansion in the universe suggested by recent
astronomical observations. One of the key differences between quintessence and
a cosmological constant is that the energy density in quintessence,
, could be a significant fraction of the overall energy even in
the early universe, while the cosmological constant will be dynamically
relevant only at late times. We use standard Big Bang Nucleosynthesis and the
observed abundances of primordial nuclides to put constraints on
at temperatures near . We point out that current experimental data
does not support the presence of such a field, providing the strong constraint
at C.L. and strengthening previous
results. We also consider the effect a scaling field has on CMB anisotropies
using the recent data from Boomerang and DASI, providing the CMB constraint
at during the radiation dominated epoch.Comment: 5 pages, 4 figures. The revised version includes the new Boomerang
and DASI dat
Calagem e adubação fosfatada favorecem o crescimento do capim-limão, Cymbopogon citratus (DC) Stapf
Calcium levels and calcium: available phosphorus ratios in diets for white egg layers from 42 to 58 weeks of age
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