111 research outputs found
Constraints on Galileon-induced precessions from solar system orbital motions
We use latest data from solar system planetary orbital motions to put
constraints on some Galileon-induced precessional effects. Due to the
Vainshtein mechanism, the Galileon-type spherically symmetric field of a
monopole induces a small, screened correction proprtional to \sqrt{r} to its
usual r^-1 Newtonian potential which causes a secular precession of the
pericenter of a test particle. In the case of our solar system, latest data
from Mars allow to constrain the magnitude of such an interaction down to
\alpha <= 0.3 level. Another Galileon-type effect which might impact solar
system dynamics is due to an unscreened constant gradient induced by the
peculiar motion of the Galaxy. The magnitude of such an effect, depending on
the different gravitational binding energies of the Sun and the planets, is \xi
<= 0.004 from the latest bounds on the supplementary perihelion precession of
Saturn.Comment: LaTex2e, 11 pages, 1 table, no figures, 35 references. To appear in
Journal of Cosmology and Astroparticle Physics (JCAP
Cosmological expansion and local systems: a Lema\^{i}tre-Tolman-Bondi model
We propose a Lema\^{i}tre-Tolman-Bondi system mimicking a two-body system to
address the problem of the cosmological expansion versus local dynamics. This
system is strongly bound but participates in the cosmic expansion and is
exactly comoving with the cosmic substratum
Phenomenology of -CDM model: a possibility of accelerating Universe with positive pressure
Among various phenomenological models, a time-dependent model is selected here to investigate the -CDM cosmology.
Using this model the expressions for the time-dependent equation of state
parameter and other physical parameters are derived. It is shown that
in model accelerated expansion of the Universe takes place at negative
energy density, but with a positive pressure. It has also been possible to
obtain the change of sign of the deceleration parameter during cosmic
evolution.Comment: 16 Latex pages, 11 figures, Considerable modifications in the text;
Accepted in IJT
Cosmological parameters from large scale structure - geometric versus shape information
The matter power spectrum as derived from large scale structure (LSS) surveys
contains two important and distinct pieces of information: an overall smooth
shape and the imprint of baryon acoustic oscillations (BAO). We investigate the
separate impact of these two types of information on cosmological parameter
estimation, and show that for the simplest cosmological models, the broad-band
shape information currently contained in the SDSS DR7 halo power spectrum (HPS)
is by far superseded by geometric information derived from the baryonic
features. An immediate corollary is that contrary to popular beliefs, the upper
limit on the neutrino mass m_\nu presently derived from LSS combined with
cosmic microwave background (CMB) data does not in fact arise from the possible
small-scale power suppression due to neutrino free-streaming, if we limit the
model framework to minimal LambdaCDM+m_\nu. However, in more complicated
models, such as those extended with extra light degrees of freedom and a dark
energy equation of state parameter w differing from -1, shape information
becomes crucial for the resolution of parameter degeneracies. This conclusion
will remain true even when data from the Planck surveyor become available. In
the course of our analysis, we introduce a new dewiggling procedure that allows
us to extend consistently the use of the SDSS HPS to models with an arbitrary
sound horizon at decoupling. All the cases considered here are compatible with
the conservative 95%-bounds \sum m_\nu < 1.16 eV, N_eff = 4.8 \pm 2.0.Comment: 18 pages, 4 figures; v2: references added, matches published versio
Holographic Dark Energy Model and Scalar-Tensor Theories
We study the holographic dark energy model in a generalized scalar tensor
theory. In a universe filled with cold dark matter and dark energy, the effect
of potential of the scalar field is investigated in the equation of state
parameter. We show that for a various types of potentials, the equation of
state parameter is negative and transition from deceleration to acceleration
expansion of the universe is possible.Comment: 11 pages, no figure. To appear in General Relativity and Gravitatio
Gauge Formulation for Higher Order Gravity
This work is an application of the second order gauge theory for the Lorentz
group, where a description of the gravitational interaction is obtained which
includes derivatives of the curvature. We analyze the form of the second field
strenght, , in terms of geometrical variables. All possible
independent Lagrangians constructed with quadratic contractions of and
quadratic contractions of are analyzed. The equations of motion for a
particular Lagrangian, which is analogous to Podolsky's term of his Generalized
Electrodynamics, are calculated. The static isotropic solution in the linear
approximation was found, exhibiting the regular Newtonian behaviour at short
distances as well as a meso-large distance modification.Comment: Published versio
Interaction of Hawking radiation with static sources in deSitter and Schwarzschild-deSitter spacetimes
We study and look for similarities between the response rates and of a static scalar source
with constant proper acceleration interacting with a massless,
conformally coupled Klein-Gordon field in (i) deSitter spacetime, in the
Euclidean vacuum, which describes a thermal flux of radiation emanating from
the deSitter cosmological horizon, and in (ii) Schwarzschild-deSitter
spacetime, in the Gibbons-Hawking vacuum, which describes thermal fluxes of
radiation emanating from both the hole and the cosmological horizons,
respectively, where is the cosmological constant and is the black
hole mass. After performing the field quantization in each of the above
spacetimes, we obtain the response rates at the tree level in terms of an
infinite sum of zero-energy field modes possessing all possible angular
momentum quantum numbers. In the case of deSitter spacetime, this formula is
worked out and a closed, analytical form is obtained. In the case of
Schwarzschild-deSitter spacetime such a closed formula could not be obtained,
and a numerical analysis is performed. We conclude, in particular, that and do not coincide in
general, but tend to each other when or . Our
results are also contrasted and shown to agree (in the proper limits) with
related ones in the literature.Comment: ReVTeX4 file, 9 pages, 5 figure
Cosmic Acceleration in Brans-Dicke Cosmology
We consider Brans-Dicke theory with a self-interacting potential in Einstein
conformal frame. We show that an accelerating expansion is possible in a
spatially flat universe for large values of the Brans-Dicke parameter
consistent with local gravity experiments.Comment: 10 Pages, 3 figures, To appear in General Relativity and Gravitatio
Do WMAP data favor neutrino mass and a coupling between Cold Dark Matter and Dark Energy?
Within the frame of cosmologies where Dark Energy (DE) is a self--interacting
scalar field, we allow for a CDM--DE coupling and non--zero neutrino masses,
simultaneously. In their 0--0 version, i.e. in the absence of coupling and
neutrino mass, these cosmologies provide an excellent fit to WMAP, SNIa and
deep galaxy sample spectra, at least as good as \LambdaCDM. When the new
degrees of freedom are open, we find that CDM--DE coupling and significant
neutrino masses (~0.1eV per \nu species) are at least as likely as the 0--0
option and, in some cases, even statistically favoured. Results are obtained by
using a Monte Carlo Markov Chain approach.Comment: 18 pages, 10 figures, submitted to JCA
Deviation From \Lambda CDM With Cosmic Strings Networks
In this work, we consider a network of cosmic strings to explain possible
deviation from \Lambda CDM behaviour. We use different observational data to
constrain the model and show that a small but non zero contribution from the
string network is allowed by the observational data which can result in a
reasonable departure from \Lambda CDM evolution. But by calculating the
Bayesian Evidence, we show that the present data still strongly favour the
concordance \Lambda CDM model irrespective of the choice of the prior.Comment: 15 Pages, Latex Style, 4 eps figures, Revised Version, Accepted for
publication in European Physical Journal
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