222 research outputs found
CMB Constraints on a Stochastic Background of Primordial Magnetic Fields
We constrain a stochastic background of primordial magnetic field (PMF) by
its contribution to the angular power spectrum of cosmic microwave background
anisotropies. We parametrize such stochastic background by a power-law spectrum
with index and by its Gaussian smoothed amplitude on a
comoving length . We give an approximation for the spectra of the
relevant correlators of the energy-momentum of the stochastic background of PMF
for any . By using the WMAP 7 year data in combination with ACBAR, BICEP
and QUAD we obtain the constraint nG at 95% confidence
level for a stochastic background of non-helical PMF. We discuss the relative
importance of the scalar and vector contribution to CMB anisotropies in
obtaining these constraints. We then forecast {\sc Planck} capabilities in
constraining .Comment: 13 pages, 7 figures, 3 tables. Revised version accepted for
publication in Phys. Rev. D, conclusions unchange
On the dipole straylight contamination in spinning space missions dedicated to CMB anisotropy
We present an analysis of the dipole straylight contamination (DSC) for
spinning space-missions designed to measure CMB anisotropies. Although this
work is mainly devoted to the {\sc Planck} project, it is relatively general
and allows to focus on the most relevant DSC implications. We first study a
simple analytical model for the DSC in which the pointing direction of the main
spillover can be assumed parallel or not to the spacecraft spin axis direction
and compute the time ordered data and map. The map is then analysed paying
particular attention to the DSC of the low multipole coefficients of the map.
Through dedicated numerical simulations we verify the analytical results and
extend the analysis to higher multipoles and to more complex (and realistic)
cases by relaxing some of the simple assumptions adopted in the analytical
approach. We find that the systematic effect averages out in an even number of
surveys, except for a contamination of the dipole itself that survives when
spin axis and spillover directions are not parallel and for a contamination of
the other multipoles in the case of complex scanning strategies. In particular,
the observed quadrupole can be affected by the DSC in an odd number of surveys
or in the presence of survey uncompleteness or over-completeness. Various
aspects relevant in CMB space projects (such as implications for calibration,
impact on polarization measurements, accuracy requirement in the far beam
knowledge for data analysis applications, scanning strategy dependence) are
discussed.Comment: 21 pages, 13 Figures, 1 Table. To appear in MNRAS. Accepted 2006 July
13. Received 2006 July 13; in original form 2006 June 7. This work has been
done in the framework of the Planck LFI activitie
Cosmological constraints on induced gravity dark energy models
We study induced gravity dark energy models coupled with a simple monomial
potential and a positive exponent . These simple
potentials lead to viable dark energy models with a weak dependence on the
exponent, which characterizes the accelerated expansion of the cosmological
model in the asymptotic attractor, when ordinary matter becomes negligible. We
use recent cosmological data to constrain the coupling to the Ricci
curvature, under the assumptions that the scalar field starts at rest deep in
the radiation era and that the gravitational constant in the Einstein equations
is compatible with the one measured in a Cavendish-like experiment. By using
2015 data only, we obtain the 95 % CL bound for
, which is further tightened to by adding Baryonic
Acoustic Oscillations (BAO) data. This latter bound improves by % the
limit obtained with the 2013 data and the same compilation of BAO
data. We discuss the dependence of the and on
.Comment: 16 pages, 10 figure
CMB and BAO constraints for an induced gravity dark energy model with a quartic potential
We study the predictions for structure formation in an induced gravity dark
energy model with a quartic potential. By developing a dedicated
Einstein-Boltzmann code, we study self-consistently the dynamics of homogeneous
cosmology and of linear perturbations without using any parametrization. By
evolving linear perturbations with initial conditions in the radiation era, we
accurately recover the quasi-static analytic approximation in the matter
dominated era. We use Planck 2013 data and a compilation of baryonic acoustic
oscillation (BAO) data to constrain the coupling to the Ricci
curvature and the other cosmological parameters. By connecting the
gravitational constant in the Einstein equation to the one measured in a
Cavendish-like experiment, we find at 95% CL with Planck 2013
and BAO data. This is the tightest cosmological constraint on and on
the corresponding derived post-Newtonian parameters. Because of a degeneracy
between and the Hubble constant , we show how larger values for
are allowed, but not preferred at a significant statistical level,
when local measurements of are combined in the analysis with Planck 2013
data.Comment: 13 pages, 7 figure
Constraints on primordial magnetic fields from magnetically-induced perturbations: current status and future perspectives with LiteBIRD and future ground based experiments
We present the constraints on the amplitude of magnetic fields generated
prior to the recombination using CMB temperature and polarization anisotropy
data from Planck 2018 release, alone and in combination with those from
BICEP2/Keck array and the South Pole Telescope. We model the fields with a
generic parametrization and we make no assumptions on their origin in order to
provide general constraints on their characteristics. The analysis updates the
former corresponding Planck 2015 results both on data and numerical
implementation. We then perform forecasts for the next generation of CMB
experiments such as LiteBIRD satellite alone and in combination with future
ground based experiments.Comment: 26 pages, 9 figure
- …