919 research outputs found
Population dynamics and adaptative strategies of Martiodrilus carimaguensis (Oligochaeta, Glossoscolecidae), a native species from the well-drained savannas of Colombia
#Martiodrilus carimaguensis (Oligochaeta, Glossoscolecidae) is a large, anecic native earthworm species which was found in natural and disturbed savannas in the Oxisols of the Colombian Llanos. Its population dynamics were studied in a native savanna, and in a 17 year old grazed grass-legume pasture where density and biomass were higher. Monthly cast deposition on the soil surface in the improved pasture was 38.4 x 10(exp 3) fresh casts/ha, eleven times more than in the native savanna. A strong relationship was found between numbers of #M. carimaguensis and numbers of fresh surface casts. Different patterns of adaptation to the dry season were observed for adults and juveniles. Adults are active for eight months whereas juveniles enter diapause 3-4 months earlier. The vertical distribution pattern of the earthworm population also shows marked seasonal changes. (Résumé d'auteur
The effective Lagrangian of dark energy from observations
Using observational data on the expansion rate of the universe (H(z)) we
constrain the effective Lagrangian of the current accelerated expansion. Our
results show that the effective potential is consistent with being flat i.e., a
cosmological constant; it is also consistent with the field moving along an
almost flat potential like a pseudo-Goldstone boson. We show that the potential
of dark energy does not deviate from a constant at more than 6% over the
redshift range 0 < z < 1. The data can be described by just a constant term in
the Lagrangian and do not require any extra parameters; therefore there is no
evidence for augmenting the number of parameters of the LCDM paradigm. We also
find that the data justify the effective theory approach to describe
accelerated expansion and that the allowed parameters range satisfy the
expected hierarchy. Future data, both from cosmic chronometers and baryonic
acoustic oscillations, that can measure H(z) at the % level, could greatly
improve constraints on the flatness of the potential or shed some light on
possible mechanisms driving the accelerated expansion. Besides the above
result, it is shown that the effective Lagrangian of accelerated expansion can
be constrained from cosmological observations in a model-independent way and
that direct measurements of the expansion rate H(z) are most useful to do so.Comment: 9 pages, 3 figures, JCAP submitted. This paper presents a
reconstruction of the dark energy potential. It is a companion to Moresco et
al. 2012a, which presents new H(z) results and Moresco et al. 2012b, which
provides cosmological parameter constraint
Cosmic Chronometers: Constraining the Equation of State of Dark Energy. I: H(z) Measurements
We present new determinations of the cosmic expansion history from
red-envelope galaxies. We have obtained for this purpose high-quality spectra
with the Keck-LRIS spectrograph of red-envelope galaxies in 24 galaxy clusters
in the redshift range 0.2 < z < 1.0. We complement these Keck spectra with
high-quality, publicly available archival spectra from the SPICES and VVDS
surveys. We improve over our previous expansion history measurements in Simon
et al. (2005) by providing two new determinations of the expansion history:
H(z) = 97 +- 62 km/sec/Mpc at z = 0.5 and H(z) = 90 +- 40 km/sec/Mpc at z =
0.8. We discuss the uncertainty in the expansion history determination that
arises from uncertainties in the synthetic stellar-population models. We then
use these new measurements in concert with cosmic-microwave-background (CMB)
measurements to constrain cosmological parameters, with a special emphasis on
dark-energy parameters and constraints to the curvature. In particular, we
demonstrate the usefulness of direct H(z) measurements by constraining the
dark- energy equation of state parameterized by w0 and wa and allowing for
arbitrary curvature. Further, we also constrain, using only CMB and H(z) data,
the number of relativistic degrees of freedom to be 4 +- 0.5 and their total
mass to be < 0.2 eV, both at 1-sigma.Comment: Submitted to JCA
Observational Constraints to Ricci Dark Energy Model by Using: SN, BAO, OHD, fgas Data Sets
In this paper, we perform a global constraint on the Ricci dark energy model
with both the flat case and the non-flat case, using the Markov Chain Monte
Carlo (MCMC) method and the combined observational data from the cluster X-ray
gas mass fraction, Supernovae of type Ia (397), baryon acoustic oscillations,
current Cosmic Microwave Background, and the observational Hubble function. In
the flat model, we obtain the best fit values of the parameters in regions: ,
, , . In the non-flat
model, the best fit parameters are found in
regions:,
, , ,
. Compared to the constraint results in
the model by using the same datasets, it is shown that
the current combined datasets prefer the model to the
Ricci dark energy model.Comment: 12 pages, 3 figure
Constraining the expansion rate of the Universe using low-redshift ellipticals as cosmic chronometers
We present a new methodology to determine the expansion history of the
Universe analyzing the spectral properties of early type galaxies (ETG). We
found that for these galaxies the 4000\AA break is a spectral feature that
correlates with the relative ages of ETGs. In this paper we describe the
method, explore its robustness using theoretical synthetic stellar population
models, and apply it using a SDSS sample of 14 000 ETGs. Our motivation
to look for a new technique has been to minimise the dependence of the cosmic
chronometer method on systematic errors. In particular, as a test of our
method, we derive the value of the Hubble constant (stat)
(syst) (68% confidence), which is not only fully compatible with the
value derived from the Hubble key project, but also with a comparable error
budget. Using the SDSS, we also derive, assuming w=constant, a value for the
dark energy equation of state parameter (stat)
(syst). Given the fact that the SDSS ETG sample only reaches , this
result shows the potential of the method. In future papers we will present
results using the high-redshift universe, to yield a determination of H(z) up
to .Comment: 25 pages, 17 figures, JCAP accepte
New constraints on cosmological parameters and neutrino properties using the expansion rate of the Universe to z~1.75
We have assembled a compilation of observational Hubble parameter
measurements estimated with the differential evolution of cosmic chronometers,
in the redshift range 0<z<1.75. This sample has been used, in combination with
CMB data and with the most recent estimate of the Hubble constant H_0, to
derive new constraints on several cosmological parameters. The new Hubble
parameter data are very useful to break some of the parameter degeneracies
present in CMB-only analysis, and to constrain possible deviations from the
standard (minimal) flat \Lambda CDM model. The H(z) data are especially
valuable in constraining \Omega_k and \Omega_DE in models that allow a
variation of those parameters, yielding constraints that are competitive with
those obtained using Supernovae and/or baryon acoustic oscillations. We also
find that our H(z) data are important to constrain parameters that do no affect
directly the expansion history, by breaking or reducing degeneracies with other
parameters. We find that Nrel=3.45\pm0.33 using WMAP 7-years data in
combination with South Pole Telescope data and our H(z) determinations
(Nrel=3.71\pm0.45 using Atacama Cosmology Telescope data instead of South Pole
Telescope). We exclude Nrel>4 at 95% CL (74% CL) using the same datasets
combinations. We also put competitive limits on the sum of neutrino masses,
\Sigma m_\nu<0.24 eV at 68% confidence level. These results have been proven to
be extremely robust to many possible systematic effects, such as the initial
choice of stellar population synthesis model adopted to estimate H(z) and the
progenitor-bias.Comment: 18 pages, 17 figures, 7 tables, published in JCAP. It is a companion
to Moresco et al. (2012a, http://arxiv.org/abs/1201.3609) and Jimenez et al.
(2012, http://arxiv.org/abs/1201.3608). The H(z) data can be downloaded at
http://www.physics-astronomy.unibo.it/en/research/areas/astrophysics/cosmology-with-cosmic-chronometer
Constraints on the CMB temperature redshift dependence from SZ and distance measurements
The relation between redshift and the CMB temperature,
is a key prediction of standard cosmology, but is violated in many non-standard
models. Constraining possible deviations to this law is an effective way to
test the CDM paradigm and search for hints of new physics. We present
state-of-the-art constraints, using both direct and indirect measurements. In
particular, we point out that in models where photons can be created or
destroyed, not only does the temperature-redshift relation change, but so does
the distance duality relation, and these departures from the standard behaviour
are related, providing us with an opportunity to improve constraints. We show
that current datasets limit possible deviations of the form
to be up to a redshift
. We also discuss how, with the next generation of space and
ground-based experiments, these constraints can be improved by more than one
order of magnitude.Comment: 27 pages, 11 figure
Observational constraints on holographic dark energy with varying gravitational constant
We use observational data from Type Ia Supernovae (SN), Baryon Acoustic
Oscillations (BAO), Cosmic Microwave Background (CMB) and observational Hubble
data (OHD), and the Markov Chain Monte Carlo (MCMC) method, to constrain the
cosmological scenario of holographic dark energy with varying gravitational
constant. We consider both flat and non-flat background geometry, and we
present the corresponding constraints and contour-plots of the model
parameters. We conclude that the scenario is compatible with observations. In
1 we find ,
, and
, while for the present value
of the dark energy equation-of-state parameter we obtain
.Comment: 12 pages, 2 figures, version published in JCA
Bianchi Type III Anisotropic Dark Energy Models with Constant Deceleration Parameter
The Bianchi type III dark energy models with constant deceleration parameter
are investigated. The equation of state parameter is found to be time
dependent and its existing range for this model is consistent with the recent
observations of SN Ia data, SN Ia data (with CMBR anisotropy) and galaxy
clustering statistics. The physical aspect of the dark energy models are
discussed.Comment: 12 pages, 2 figures, Accepted version of IJT
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