421 research outputs found
CMB and Cosmological Parameters: Current Status and Prospects
The last years have been an exciting period for the field of the Cosmic
Microwave Background (CMB) research. With recent CMB balloon-borne and
ground-based experiments we are entering a new era of 'precision' cosmology
that enables us to use the CMB anisotropy measurements to constrain the
cosmological parameters and test new theoretical scenarios.Comment: 21 pages, 5 figures. Based on an invited review at the XIII
Rencontres de Blois - Frontiers of the Universe, June 17-23,200
First cosmological constraints combining Planck with the recent gravitational-wave standard siren measurement of the Hubble constant
The recent observations of gravitational-wave and electromagnetic emission
produced by the merger of the binary neutron-star system GW170817 have opened
the possibility of using standard sirens to constrain the value of the Hubble
constant. While the reported bound of at C.L. is
significantly weaker than those recently derived by observations of Cepheid
variables, it does not require any form of cosmic distance ladder and can be
considered as complementary and, in principle, more conservative. Here we
combine, for the first time, the new measurement with the Planck Cosmic
Microwave Background observations in a parameters extended CDM
scenario, where the Hubble constant is weakly constrained from CMB data alone
and bound to a low value km/s/Mpc at C.L. We point
out that the non-Gaussian shape of the GW170817 bound makes lower values of the
Hubble constant in worst agreement with observations than what expected from a
Gaussian form. The inclusion of the new GW170817 Hubble constant measurement
therefore significantly reduces the allowed parameter space, improving the
cosmological bounds on several parameters as the neutrino mass, curvature and
the dark energy equation of state.Comment: 5 pages, 4 Figures, few typos correcte
Planck constraints on neutrino isocurvature density perturbations
The recent Cosmic Microwave Background data from the Planck satellite
experiment, when combined with HST determinations of the Hubble constant, are
compatible with a larger, non-standard, number of relativistic degrees of
freedom at recombination, parametrized by the neutrino effective number
. In the curvaton scenario, a larger value for could arise
from a non-zero neutrino chemical potential connected to residual neutrino
isocurvature density (NID) perturbations after the decay of the curvaton field,
parametrized by the amplitude . Here we present new constraints
on and from an analysis of recent cosmological data.
We found that the Planck+WP dataset does not show any indication for a neutrino
isocurvature component, severly constraining its amplitude, and that current
indications for a non-standard are further relaxed.Comment: 5 pages, 3 figure
Is Cosmology Compatible with Blue Gravity Waves ?
A primordial gravitational wave background with positive(blue) spectral index
is expected in several non-standard inflationary cosmologies where the
stress-energy tensor violates the null energy condition. Here we show that a
sizable amount of blue gravitational waves is compatible with current
cosmological and astrophysical data. So far most of the works on parameter
estimation from cosmic microwave background data have assumed a negative or
negligible spectral index. The present limits on cosmological parameters,
especially on the scalar spectral index, widen up considerably when one allows
also for blue tilts of the tensor spectrum. Since the amplitude of the CMB
B-mode polarization is larger in these models, future data from Planck are
likely to provide crucial measurements.Comment: 5 Pages, 5 Figure
The generation: present and future constraints on neutrino masses from cosmology and laboratory experiments
We perform a joint analysis of current data from cosmology and laboratory
experiments to constrain the neutrino mass parameters in the framework of
bayesian statistics, also accounting for uncertainties in nuclear modeling,
relevant for neutrinoless double decay () searches. We find
that a combination of current oscillation, cosmological and data
constrains () at 95\% C.L. for normal (inverted)
hierarchy. This result is in practice dominated by the cosmological and
oscillation data, so it is not affected by uncertainties related to the
interpretation of data, like nuclear modeling, or the exact
particle physics mechanism underlying the process. We then perform forecasts
for forthcoming and next-generation experiments, and find that in the case of
normal hierarchy, given a total mass of eV, and assuming a
factor-of-two uncertainty in the modeling of the relevant nuclear matrix
elements, it will be possible to measure the total mass itself, the effective
Majorana mass and the effective electron mass with an accuracy (at 95\% C.L.)
of , , respectively, as well as to be
sensitive to one of the Majorana phases. This assumes that neutrinos are
Majorana particles and that the mass mechanism gives the dominant contribution
to decay. We argue that more precise nuclear modeling will be
crucial to improve these sensitivities.Comment: v2: 6 pages, 3 figures, 1 table; added definition of parameter
minimal value from oscillation measurements; corrected confidence interval,
that in v1 were reported at 90% C.L. and misidentified as 95% C.L.; accepted
for publicatio
Cosmic Microwave Background Anisotropies from Global Texture
We investigate the global texture model of structure formation in cosmogonies
with non-zero cosmological constant for different values of the Hubble
parameter. We find that the absence of significant acoustic peaks and little
power on large scales are robust predictions of these models. However, from a
careful comparison with experiments we conclude that at present we cannot
safely reject the model on the grounds of published CMB anisotropy data.
If bias is close to one on large scales, galaxy correlation data rules out
the models. New, very stringent constraints come from peculiar velocities.
Investigating the large-N limit, we argue that our main conclusions apply to
all global O(N) models of structure formation.Comment: 20 page LaTeX file, 11 postscript figs. included, proceedings to the
EC conference on 3K Cosmology in Rome, Oct. 9
Did Boomerang hit MOND?
Purely baryonic dark matter dominated models like MOND based on modification
of Newtonian gravity have been successfully in reproducing some dynamical
properties of galaxies. More recently, a relativistic formulation of MOND
proposed by Bekenstein seems to agree with cosmological large scale structure
formation. In this work, we revise the agreement of MOND with observations in
light of the new results on the Cosmic Microwave Anisotropies provided by the
2003 flight of Boomerang. The measurements of the height of the third acoustic
peak, provided by several small scale CMB experiments have reached enough
sensitivity to severely constrain models without cold dark matter. Assuming
that acoustic peak structure in the CMB is unchanged and that local
measurements of the Hubble constant can be applied, we find that the cold dark
matter is strongly favoured with Bayesian probability ratio of about one in two
hundred.Comment: 5 pages, 2 figures; v2 minor modifications to match version published
as "Test of modified newtonian dynamics with recent Boomerang data." in PRD
rapid com
When Did Cosmic Acceleration Start ?
A precise determination, and comparison, of the epoch of the onset of cosmic
acceleration, at redshift z_acc, and of dark energy domination, at z_eq,
provides an interesting measure with which to parameterize dark energy models.
By combining several cosmological datasets we place constraints on the redshift
and age of cosmological acceleration. For a Lambda-CDM model, we find the
constraint z_acc=0.76\pm0.10 at 95% c.l., occurring 6.7\pm0.4 Gyrs ago.
Allowing a constant equation of state but different from -1 changes the
constraints to z_acc=0.81\pm0.12 (6.9\pm0.5 Gyrs ago) and
z_eq=0.48\pm0.14(4.9\pm0.9 Gyrs ago), while dynamical models markedly increase
the error on the constraints with z_acc=0.81\pm0.30 (6.8\pm1.4 Gyrs ago) and
z_eq=0.44\pm0.20 (4.5\pm1.0 Gyrs ago). Unified dark energy models as Silent
Quartessence yield: z_acc=0.80\pm0.16 (6.8\pm0.6 Gyrs ago).Comment: 5 pages, 2 figure
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