620 research outputs found
Galactic dust polarized emission at high latitudes and CMB polarization
We estimate the dust polarized emission in our galaxy at high galactic
latitudes, which is the dominant foreground for measuring CMB polarization
using the high frequency instrument (HFI) aboard Planck surveyor. We compare it
with the level of CMB polarization and conclude that, for angular scales , the scalar-induced CMB polarization and temperature-polarization
cross-correlation are much larger than the foreground level at . The tensor-induced signals seem to be at best comparable to the
foreground level.}Comment: Latex document, 4 pages, 2 figures, to appear in "Fundamental
parameters in Cosmology", Rencontres de Moriond, 199
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
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
CMB Polarization can constrain cosmology better than CMB temperature
We demonstrate that for a cosmic variance limited experiment, CMB E
polarization alone places stronger constraints on cosmological parameters than
CMB temperature. For example, we show that EE can constrain parameters better
than TT by up to a factor 2.8 when a multipole range of l=30-2500 is
considered. We expose the physical effects at play behind this remarkable
result and study how it depends on the multipole range included in the
analysis. In most relevant cases, TE or EE surpass the TT based cosmological
constraints. This result is important as the small scale astrophysical
foregrounds are expected to have a much reduced impact on polarization, thus
opening the possibility of building cleaner and more stringent constraints of
the LCDM model. This is relevant specially for proposed future CMB satellite
missions, such as CORE or PRISM, that are designed to be cosmic variance
limited in polarization till very large multipoles. We perform the same
analysis for a Planck-like experiment, and conclude that even in this case TE
alone should determine the constraint on better than TT by 15%,
while determining , and with comparable accuracy.
Finally, we explore a few classical extensions of the LCDM model and show again
that CMB polarization alone provides more stringent constraints than CMB
temperature in case of a cosmic variance limited experiment.Comment: 14 pages, 16 figure
Water-compatible synthesis of 2-trifluoromethyl-1,3-dioxanes
A water-compatible method for the diastereoselective
synthesis of 2-trifluormethyl-1,3-dioxanes is described. The reaction
proceeds under mild reaction conditions using simple inorganic
bases; it has a very good substrate scope and can be performed
with different Michael acceptors. Additionally, the reaction products
can be further functionalized, showing an excellent perspective for
future applications
Constraints on mode couplings and modulation of the CMB with WMAP data
We investigate a possible asymmetry in the statistical properties of the
cosmic microwave background temperature field and to do so we construct an
estimator aiming at detecting a dipolar modulation. Such a modulation is found
to induce correlations between multipoles with . Applying this
estimator, to the V and W bands of the WMAP data, we found a significant
detection in the V band. We argue however that foregrounds and in particular
point sources are the origin of this signal.Comment: 14 pages, 14 figure
MASTER of the CMB Anisotropy Power Spectrum: A Fast Method for Statistical Analysis of Large and Complex CMB Data Sets
We describe a fast and accurate method for estimation of the cosmic microwave
background (CMB) anisotropy angular power spectrum --- Monte Carlo Apodised
Spherical Transform EstimatoR. Originally devised for use in the interpretation
of the Boomerang experimental data, MASTER is both a computationally efficient
method suitable for use with the currently available CMB data sets (already
large in size, despite covering small fractions of the sky, and affected by
inhomogeneous and correlated noise), and a very promising application for the
analysis of very large future CMB satellite mission products.Comment: 20 pages, 6 fig; submitted to ApJ; uses aastex.cls and psfig.sty
(included
Error estimation for the MAP experiment
We report here the first full sky component separation and CMB power spectrum
estimation using a Wiener filtering technique on simulated data from the
upcoming MAP experiment, set to launch in early 2001. The simulations included
contributions from the three dominant astrophysical components expected in the
five MAP spectral bands, namely CMB radiation, Galactic dust, and synchrotron
emission. We assumed a simple homogeneous and isotropic white noise model and
performed our analysis up to a spherical harmonic multipole lmax=512 on the
fraction of the sky defined by b>20 degrees. We find that the reconstruction
errors are reasonably well fitted by a Gaussian with an rms of 24 K, but
with significant deviations in the tails. Our results further support the
predictions on the resulting CMB power spectrum of a previous estimate by
Bouchet and Gispert (1999), which entailed a number of assumptions this work
removes.Comment: 5 pages, 3 color figures, version accepted in A&A Letter
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