666 research outputs found
New constraints on parity symmetry from a re-analysis of the WMAP-7 low-resolution power spectra
8 páginas, 6 figuras, 3 tablas.-- El Pdf del archivo es la versión pre-print: arXiv:1006.1979v2 .-- et al.The parity symmetry of the cosmic microwave background (CMB) pattern as seen by Wilkinson Microwave Anisotropy Probe 7 yr (WMAP 7 yr) is tested jointly in temperature and polarization at large angular scale. A quadratic maximum likelihood (QML) estimator is applied to the WMAP 7-yr low-resolution maps to compute all polarized CMB angular power spectra. The analysis is supported by 10 000 realistic Monte Carlo realizations. We confirm the previously reported parity anomaly for TT in the range δℓ=[2, 22] at >99.5 per cent C.L. No anomalies have been detected in TT for a wider ℓ range (up to ℓmax= 40). No violations have been found for EE, TE and BB which we test here for the first time. The cross-spectra TB and EB are found to be consistent with zero. We also forecast Planck capabilities in probing parity violations on low-resolution maps.Support for LAMBDA
is provided by the NASA Office of Space Science. This work was
supported by ASI through ASI/INAF Agreement I/072/09/0 for the
Planck LFI Activity of Phase E2.Peer reviewe
Hemispherical power asymmetries in the WMAP 7-year low-resolution temperature and polarization maps
We test the hemispherical power asymmetry of the WMAP 7-year low-resolution
temperature and polarization maps. We consider two natural estimators for such
an asymmetry and exploit our implementation of an optimal angular power
spectrum estimator for all the six CMB spectra. By scanning the whole sky
through a sample of 24 directions, we search for asymmetries in the power
spectra of the two hemispheres, comparing the results with Monte Carlo
simulations drawn from the WMAP 7-year best-fit model. Our analysis extends
previous results to the polarization sector. The level of asymmetry on the ILC
temperature map is found to be compatible with previous results, whereas no
significant asymmetry on the polarized spectra is detected. Moreover, we show
that our results are only weakly affected by the a posteriori choice of the
maximum multipole considered for the analysis. We also forecast the capability
to detect dipole modulation by our methodology at Planck sensitivity.Comment: 7 pages, 9 figures. Accepted for publication in MNRA
Cosmological Parameters from a re-analysis of the WMAP-7 low resolution maps
Cosmological parameters from WMAP 7 year data are re-analyzed by substituting
a pixel-based likelihood estimator to the one delivered publicly by the WMAP
team. Our pixel based estimator handles exactly intensity and polarization in a
joint manner, allowing to use low-resolution maps and noise covariance matrices
in at the same resolution, which in this work is 3.6. We
describe the features and the performances of the code implementing our
pixel-based likelihood estimator. We perform a battery of tests on the
application of our pixel based likelihood routine to WMAP publicly available
low resolution foreground cleaned products, in combination with the WMAP
high- likelihood, reporting the differences on cosmological parameters
evaluated by the full WMAP likelihood public package. The differences are not
only due to the treatment of polarization, but also to the marginalization over
monopole and dipole uncertainties implemented in the WMAP 7 year pixel
likelihood code for temperature. The credible central value for the
cosmological parameters change below the 1 level with respect to the
evaluation by the full WMAP 7 year likelihood code, with the largest difference
in a shift to smaller values of the scalar spectral index .Comment: Revised to match the version on press in MNRAS. Different
interpretation of differences vs WMAP 7. 10 pages, 6 tables, 8 figure
An optimal estimator for the CMB-LSS angular power spectrum and its application to WMAP and NVSS data
We use a Quadratic Maximum Likelihood (QML) method to estimate the angular
power spectrum of the cross-correlation between cosmic microwave background and
large scale structure maps as well as their individual auto-spectra. We
describe our implementation of this method and demonstrate its accuracy on
simulated maps. We apply this optimal estimator to WMAP 7-year and NRAO VLA Sky
Survey (NVSS) data and explore the robustness of the angular power spectrum
estimates obtained by the QML method. With the correction of the declination
systematics in NVSS, we can safely use most of the information contained in
this survey. We then make use of the angular power spectrum estimates obtained
by the QML method to derive constraints on the dark energy critical density in
a flat CDM model by different likelihood prescriptions. When using
just the cross-correlation between WMAP 7 year and NVSS maps with 1.8
resolution, the best-fit model has a cosmological constant of approximatively
70% of the total energy density, disfavouring an Einstein-de Sitter Universe at
more than 2 CL (confidence level).Comment: 12 pages, 12 figure
New constraints on Parity Symmetry from a re-analysis of the WMAP-7 low resolution power spectra
The Parity symmetry of the Cosmic Microwave Background (CMB) pattern as seen
by WMAP 7 is tested jointly in temperature and polarization at large angular
scale. A Quadratic Maximum Likelihood (QML) estimator is applied to the WMAP 7
year low resolution maps to compute all polarized CMB angular power spectra.
The analysis is supported by 10000 realistic Monte-Carlo realizations. We
confirm the previously reported Parity anomaly for TT in the range at C.L.. No anomalies have been detected in TT for a
wider range (up to ). No violations have been found for
EE, TE and BB which we test here for the first time. The cross-spectra TB and
EB are found to be consistent with zero. We also forecast {\sc Planck}
capabilities in probing Parity violations on low resolution maps.Comment: 8 pages, 6 figures, 4 tables. Accepted for publication in MNRA
Evolution of Large Scale Curvature Fluctuations During the Perturbative Decay of the Inflaton
We study the evolution of cosmological fluctuations during and after
inflation driven by a scalar field coupled to a perfect fluid through afriction
term. During the slow-roll regime for the scalar field, the perfect fluid is
also frozen and isocurvature perturbations are generated. After the end of
inflation, during the decay of the inflaton, we find that a change in the
observationally relevant large scale curvature fluctuations is possible.Comment: 9 pages, 2 figures; v2: version published in PR
Large Scale Traces of Solar System Cold Dust on CMB Anisotropies
We explore the microwave anisotropies at large angular scales produced by the
emission from cold and large dust grains, expected to exist in the outer parts
of the Solar System, using a simple toy model for this diuse emission. Its
amplitude is constrained in the Far-IR by the COBE data and is compatible with
simulations found in the literature. We analyze the templates derived after
subtracting our model from the WMAP ILC 7 yr maps and investigate on the
cosmological implications of such a possible foreground. The anomalies related
to the low quadrupole of the angular power spectrum, the two-point correlation
function, the parity and the excess of signal found in the ecliptic plane are
significantly alleviated. An impact of this foreground for some cosmological
parameters characterizing the spectrum of primordial density perturbations,
relevant for on-going and future CMB anisotropy experiments, is found.Comment: Issue 2.0, Accepted for pub. in MNRAS, Apr 8th, 2011, (sub. Oct 4th,
2010); 10 pages, 6 Figures, 1 table; pdflatex with mn2e, AMS, natbib,
txfonts, graphic
Power Asymmetries in the Cosmic Microwave Background Temperature and Polarization patterns
We test the asymmetry of the Cosmic Microwave Background anisotropy jointly
in temperature and polarization. We study the hemispherical asymmetry,
previously found only in the temperature field, with respect to the axis
identified by Hansen et al. (2009). To this extent, we make use of the low
resolution WMAP 5 year temperature and polarization Nside=16 maps and the
optimal angular power spectrum estimator BolPol (Gruppuso et al. 2009). We
consider two simple estimators for the power asymmetry and we compare our
findings with Monte Carlo simulations which take into account the full noise
covariance matrix. We confirm an excess of power in temperature angular power
spectrum in the Southern hemisphere at a significant level, between 3 sigma and
4 sigma depending on the exact range of multipoles considered. We do not find
significant power asymmetry in the gradient (curl) component EE (BB) of
polarized angular spectra. Also cross-correlation power spectra, i.e. TE, TB,
EB, show no significant hemispherical asymmetry. We also show that the Cold
Spot found by Vielva et al. (2004) in the Southern Galactic hemisphere does not
alter the significance of the hemispherical asymmetries on multipoles which can
be probed by maps at resolution Nside=16. Although the origin of the
hemispherical asymmetry in temperature remains unclear, the study of the
polarization patter could add useful information on its explanation. We
therefore forecast by Monte Carlo the Planck capabilities in probing
polarization asymmetries.Comment: 6 pages, 7 figure
Searching for hidden mirror symmetries in CMB fluctuations from WMAP 7 year maps
We search for hidden mirror symmetries at large angular scales in the WMAP 7
year Internal Linear Combination map of CMB temperature anisotropies using
global pixel based estimators introduced for this aim. Two different axes are
found for which the CMB intensity pattern is anomalously symmetric (or
anti-symmetric) under reflection with respect to orthogonal planes at the
99.84(99.96)% CL (confidence level), if compared to a result for an arbitrary
axis in simulations without the symmetry. We have verified that our results are
robust to the introduction of the galactic mask. The direction of such axes is
close to the CMB kinematic dipole and nearly orthogonal to the ecliptic plane,
respectively. If instead the real data are compared to those in simulations
taken with respect to planes for which the maximal mirror symmetry is generated
by chance, the confidence level decreases to 92.39 (76.65)%. But when the
effect in question translates into the anomalous alignment between normals to
planes of maximal mirror (anti)-symmetry and these natural axes mentioned. We
also introduce the representation of the above estimators in the harmonic
domain, confirming the results obtained in the pixel one. The symmetry anomaly
is shown to be almost entirely due to low multipoles, so it may have a
cosmological and even primordial origin. Contrary, the anti-symmetry one is
mainly due to intermediate multipoles that probably suggests its
non-fundamental nature. We have demonstrated that these anomalies are not
connected to the known issue of the low variance in WMAP observations and we
have checked that axially symmetric parts of these anomalies are small, so that
the axes are not the symmetry ones.Comment: 18 pages, 10 figures, 2 tables. Consideration and discussion
expanded, 5 figures and 1 table added, main conclusions unchange
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