7,098 research outputs found
The impact of neutrino masses on the determination of dark energy properties
Recently, the Heidelberg-Moscow double beta decay experiment has claimed a
detection for a neutrino mass with high significance. Here we consider the
impact of this measurement on the determination of the dark energy equation of
state. By combining the Heidelberg-Moscow result with the WMAP 3-years data and
other cosmological datasets we constrain the equation of state to -1.67< w
<-1.05 at 95% c.l., ruling out a cosmological constant at more than 95% c.l..
Interestingly enough, coupled neutrino-dark energy models may be consistent
with such equation of state. While future data are certainly needed for a
confirmation of the controversial Heildelberg-Moscow claim, our result shows
that future laboratory searches for neutrino masses may play a crucial role in
the determination of the dark energy properties.Comment: 4 pages, 2 figure
Constraining Quintessence with the New CMB Data
The CMB data recently released by BOOMERANG and MAXIMA suggest that the
anisotropy spectrum has a third peak in the range 800<l_3<900. A combination of
this result with constraints from large-scale structure permit us to
differentiate between different quintessence models. In particular, we find
that inverse power law models with power \alpha >1 are disfavoured. Models with
more than 5% quintessence before last scattering require a spectral index
greater than 1. These constraints are compared with supernovae observations. We
also show that the CMB alone now provides strong evidence for an accelerating
universe.Comment: 5 pages, 5 figures, replaced with version which appears in journal.
Discussion on supernovae bounds and references adde
Massive neutrinos and dark energy
We consider the impact of the Heidelberg-Moscow claim for a detection of
neutrino mass on the determination of the dark energy equation of state. By
combining the Heidelberg-Moscow result with the WMAP 3-years data and other
cosmological datasets we constrain the equation of state to -1.67< w <-1.05 at
95% c.l., While future data are certainly needed for a confirmation of the
controversial Heildelberg-Moscow claim, our result shows that future laboratory
searches for neutrino masses may play a crucial role in the determination of
the dark energy properties.Comment: 3 pages, 1 figure, Talk given by Paolo Serra at the Neutrino
Oscillation Workshop NOW2006, Otranto, Italy, September 9-16 200
Observational constraints on an interacting dark energy model
We use observations of cosmic microwave background anisotropies, supernova
luminosities and the baryon acoustic oscillation signal in the galaxy
distribution to constrain the cosmological parameters in a simple interacting
dark energy model with a time-varying equation of state. Using a Monte Carlo
Markov Chain technique we determine the posterior likelihoods. Constraints from
the individual data sets are weak, but the combination of the three data sets
confines the interaction constant to be less than 23% of the expansion
rate of the Universe ; at 95% CL . The CMB
acoustic peaks can be well fitted even if the interaction rate is much larger,
but this requires a larger or smaller (depending on the sign of interaction)
matter density today than in the non-interacting model. Due to this degeneracy
between the matter density and the interaction rate, the only observable effect
on the CMB is a larger or smaller integrated Sachs-Wolfe (ISW) effect. While SN
or BAO data alone do not set any direct constraints on the interaction, they
exclude the models with very large matter density, and hence indirectly
constrain the interaction rate when jointly analysed with the CMB data. To
enable the analysis described in this paper, we present in a companion paper
[arXiv:0907.4981] a new systematic analysis of the early radiation era solution
to find the adiabatic initial conditions for the Boltzmann integration.Comment: 16 pages, 10 figures. V2: Improved typography (2-column format);
References and a motivation of CPL parametrization added; Accepted by MNRA
The latitude dependence of the rotation measures of NVSS sources
In this Letter I use the variation of the spread in rotation measure (RM)
with Galactic latitude to separate the Galactic from the extragalactic
contributions to RM. This is possible since the latter does not depend on
Galactic latitude. As input data I use RMs from the catalogue by Taylor, Stil,
and Sunstrum, supplemented with published values for the spread in RM
(`sigmaRM') in specific regions on the sky. I test 4 models of the free
electron column density (which I will abbreviate to `DMinf') of the Milky Way,
and the best model builds up DMinf on a characteristic scale of a few kpc from
the Sun. sigmaRM correlates well with DMinf. The measured sigmaRM can be
modelled as a Galactic contribution, consisting of a term sigmaRM,MW that is
amplified at smaller Galactic latitudes as 1/sin|b|, in a similar way to DMinf,
and an extragalactic contribution, sigmaRM,EG, that is independent of latitude.
This model is sensitive to the relative magnitudes of sigmaRM,MW and
sigmaRM,EG, and the best fit is produced by sigmaRM,MW approx. 8 rad/m^2 and
sigmaRM,EG approx. 6 rad/m^2. The 4 published values for sigmaRM as a function
of latitude suggest an even larger sigmaRM,MW contribution and a smaller
sigmaRM,EG. This result from the NVSS RMs and published sigmaRM shows that the
Galactic contribution dominates structure in RM on scales between about 1degr
-- 10degr on the sky. I work out which factors contribute to the variation of
sigmaRM with Galactic latitude, and show that the sigmaRM,EG I derived is an
upper limit. Furthermore, to explain the modelled sigmaRM,MW requires that
structure in has a 1-sigma spread <~ 0.4 microG.Comment: 6 pages, 3 figures, 1 table. Published in MNRAS Letters; the
definitive version is available at wileyonlinelibrary.com,
http://onlinelibrary.wiley.com/doi/10.1111/j.1745-3933.2010.00957.x/pd
A Possible Stellar Metallic Enhancement in Post-T Tauri Stars by a Planetesimal Bombardment
The photospheres of stars hosting planets have larger metallicity than stars
lacking planets. In the present work we study the possibility of an earlier
metal enrichment of the photospheres by means of impacting planetesimals during
the first 20-30Myr. Here we explore this contamination process by simulating
the interactions of an inward migrating planet with a disc of planetesimal
interior to its orbit. The results show the percentage of planetesimals that
fall on the star. We identified the dependence of the planet's eccentricity
() and time scale of migration () on the rate of infalling
planetesimals. For very fast migrations (yr and yr) there
is no capture in mean motion resonances, independently of the value of .
Then, due to the planet's migration the planetesimals suffer close approaches
with the planet and more than 80% of them are ejected from the system. For slow
migrations (yr and yr) the percentage of collisions with
the planet decrease with the increase of the planet's eccentricity. For
and most of the planetesimals were captured in the 2:1 resonance and
more than 65% of them collided with the star. Whereas migration of a Jupiter
mass planet to very short pericentric distances requires unrealistic high disc
masses, these requirements are much smaller for smaller migrating planets. Our
simulations for a slowly migrating 0.1 planet, even demanding
a possible primitive disc three times more massive than a primitive solar
nebula, produces maximum [Fe/H] enrichments of the order of 0.18 dex. These
calculations open possibilities to explain hot Jupiters exoplanets
metallicities.Comment: Accepted for publication by Monthly Notices of the Royal Astronomical
Societ
Early massive clusters and the bouncing coupled dark energy
The abundance of the most massive objects in the Universe at different epochs
is a very sensitive probe of the cosmic background evolution and of the growth
history of density perturbations, and could provide a powerful tool to
distinguish between a cosmological constant and a dynamical dark energy field.
In particular, the recent detection of very massive clusters of galaxies at
high redshifts has attracted significant interest as a possible indication of a
failure of the standard LCDM model. Several attempts have been made in order to
explain such detections in the context of non-Gaussian scenarios or interacting
dark energy models, showing that both these alternative cosmologies predict an
enhanced number density of massive clusters at high redshifts, possibly
alleviating the tension. However, all the models proposed so far also
overpredict the abundance of massive clusters at the present epoch, and are
therefore in contrast with observational bounds on the low-redshift halo mass
function. In this paper we present for the first time a new class of
interacting dark energy models that simultaneously account for an enhanced
number density of massive clusters at high redshifts and for both the standard
cluster abundance at the present time and the standard power spectrum
normalization at CMB. The key feature of this new class of models is the
"bounce" of the dark energy scalar field on the cosmological constant barrier
at relatively recent epochs. We present the background and linear perturbations
evolution of the model, showing that the standard amplitude of density
perturbations is recovered both at CMB and at the present time, and we
demonstrate by means of large N-body simulations that our scenario predicts an
enhanced number of massive clusters at high redshifts without affecting the
present halo abundance. (Abridged)Comment: 11 pages, 6 figures, 2 tables. Minor changes, references added.
Accepted for publication in MNRA
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