742 research outputs found
Parameter extraction by Planck for a CDM model with broken scale invariance and cosmological constant
We consider a class of spatially flat cold dark matter (CDM) models, with a
cosmological constant and a broken-scale-invariant (BSI) steplike primordial
spectrum of adiabatic perturbations, previously found to be in very good
agreement with observations. Performing a Fisher matrix analysis, we show that
in case of a large gravitational waves (GW) contribution some free parameters
(defining the step) of our BSI model can be extracted with remarkable accuracy
by the Planck satellite, thanks to the polarisation anisotropy measurements.
Further, cosmological parameters can still be found with very good precision,
despite a larger number of free parameters than in the simplest inflationary
models.Comment: Final version to appear in MNRAS. Minor changes. 5 pages, 1 LaTeX
figure, uses mn.st
Encircling the dark: constraining dark energy via cosmic density in spheres
The recently published analytic probability density function for the mildly
non-linear cosmic density field within spherical cells is used to build a
simple but accurate maximum likelihood estimate for the redshift evolution of
the variance of the density, which, as expected, is shown to have smaller
relative error than the sample variance. This estimator provides a competitive
probe for the equation of state of dark energy, reaching a few percent accuracy
on wp and wa for a Euclid-like survey. The corresponding likelihood function
can take into account the configuration of the cells via their relative
separations. A code to compute one-cell density probability density functions
for arbitrary initial power spectrum, top-hat smoothing and various spherical
collapse dynamics is made available online so as to provide straightforward
means of testing the effect of alternative dark energy models and initial
power-spectra on the low-redshift matter distribution.Comment: 7 pages, replaced to match the MNRAS accepted versio
Detectability of the primordial origin of the gravitational wave background in the Universe
The appearance of peaks in various primordial fluctuation Fourier power
spectra is a generic prediction of the inflationary scenario. We investigate
whether future experiments, in particular the satellite experiment PLANCK, will
be able to detect the possible appearance of these peaks in the B-mode
polarization multipole power spectrum. This would yield a conclusive proof of
the presence of a primordial background of gravitational waves.Comment: 4 pages, 1 figure, version accepted for publication in A&A.
Conclusions unchange
Polarized Microwave Emission from Dust
Polarized emission from dust is an important foreground that can hinder the
progress in polarized CMB studies unless carefully accounted for. We discuss
potential difficulties associated with the dust foreground, namely, the
existence of different grain populations with very different
emission/polarization properties and variations of the polarization yield with
grain temperature. In this context we appeal for systematic studies of
polarized dust emission as the means of dealing with this foreground.Comment: 12 pages, 4 figures, to appear in proc. of the AIP conf.
"Astrophysical Polarized Backgrouds", eds S. Cecchini, S. Cortiglioni, R.
Sault, and C. Sbarr
Initial Conditions for Large Cosmological Simulations
This technical paper describes a software package that was designed to
produce initial conditions for large cosmological simulations in the context of
the Horizon collaboration. These tools generalize E. Bertschinger's Grafic1
software to distributed parallel architectures and offer a flexible alternative
to the Grafic2 software for ``zoom'' initial conditions, at the price of large
cumulated cpu and memory usage. The codes have been validated up to resolutions
of 4096^3 and were used to generate the initial conditions of large
hydrodynamical and dark matter simulations. They also provide means to generate
constrained realisations for the purpose of generating initial conditions
compatible with, e.g. the local group, or the SDSS catalog.Comment: 12 pages, 11 figures, submitted to ApJ
CMB Polarization Data and Galactic Foregrounds: Estimation of Cosmological Parameters
We estimate the accuracy with which various cosmological parameters can be
determined from the CMB temperature and polarization data when various galactic
unpolarized and polarized foregrounds are included and marginalized using the
multi-frequency Wiener filtering technique. We use the specifications of the
future CMB missions MAP and PLANCK for our study. Our results are in
qualitative agreement with earlier results obtained without foregrounds, though
the errors in most parameters are higher because of degradation of the
extraction of polarization signal in the presence of foregrounds.Comment: 6 pages, submitted to MNRA
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