Looking for Cosmological Alfven Waves inWilkinson Microwave Anisotropy ProbeData
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Abstract:
A primordial cosmological magnetic field induces and supports vorticity or Alfvén waves, which in turn generate cosmic microwave background (CMB) anisotropies. A homogeneous primordial magnetic field with fixed direction induces correlations between the al-1,m and al+1,m multipole coefficients of the CMB temperature anisotropy field. We discuss the constraints that can be placed on the strength of such a primordial magnetic field using CMB anisotropy data from the Wilkinson Microwave Anisotropy Probe experiment. We place 3 σ upper limits on the strength of the magnetic field of B < 15 nG for vector perturbation spectral index n = -5 and B < 1.7 nG for n = -7.Keywords:
CMB cold spot
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Aims.We study the large-scale angular correlation signatures of the cosmic microwave background (CMB) temperature fluctuations from WMAP data in several spherical cap regions of the celestial sphere, outside the Kp0 or Kp2 cut-sky masks.
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The cosmic microwave background (CMB) temperature maps published by the Wilkinson Microwave Anisotropy Probe (WMAP) team are found to be inconsistent with the differential time-ordered data (TOD), from which the maps are reconstructed. The inconsistency indicates that there is a serious problem in the map making routine of the WMAP team, and it is necessary to reprocess the WMAP data. We develop a self-consistent software package of map-making and power spectrum estimation independently of the WMAP team. Our software passes a variety of tests. New CMB maps are then reconstructed, which are significantly different from the official WMAP maps. In the new maps, the inconsistency disappeared, along with the hitherto unexplained high level alignment between the CMB quadrupole and octopole components detected in released WMAP maps. An improved CMB cross-power spectrum is then derived from the new maps which better agrees with that of BOOMRANG. Two important results are hence obtained: the CMB quadrupole drops to nearly zero, and the power in multiple moment range between 200 and 675 decreases on average by about 13%, causing the best-fit cosmological parameters to change considerably, e.g., the total matter density increases from 0.26 up to 0.32 and the dark energy density decreases from 0.74 down to 0.68. These new parameters match with improved accuracy those of other independent experiments. Our results indicate that there is still room for significant revision in the cosmological model parameters.
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We stack Wilkinson Microwave Anisotropy Probe (WMAP) 7-yr temperature data around extragalactic point sources, showing that the profiles are consistent with WMAP's beam models, in disagreement with the findings of Sawangwit and Shanks. These results require the point source catalogue's selection to be free from biases due to cosmic microwave background (CMB) fluctuations. We compare profiles from sources in the standard WMAP catalogue, the WMAP catalogue selected from a CMB-free combination of data and the NRAO VLA Sky Survey catalogue, and quantify the agreement with fits to simple parametric beam models. We estimate the biases in source profiles due to alignments with positive CMB fluctuations, finding them roughly consistent with those biases found with the WMAP standard catalogue. Addressing those biases, we find source spectral indices significantly steeper than those found by WMAP, with strong evidence for spectral steepening above 61 GHz. We re-analyse parameters with a revised source correction, finding an ns increase by up to ˜0.3s. Finally, we discuss implications for current CMB experiments.
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Revisiting the oscillations in the CMB angular power spectra at $\ell\sim120$ in the Planck2015 data
While the observed nearly scale-invariant initial power spectrum is regarded as one of the favorable evidence of the standard inflationary cosmology, precision observations of the Cosmic Microwave Background (CMB) anisotropies also suggest possible existence of nontrivial features such as those observed around multipoles $\ell\sim120$ by WMAP. Here, we examine the Planck data and investigate the effects of these features on the cosmological parameter estimation performing the Markov-Chain Monte-Carlo (MCMC) analysis. We find that the features exist in the Planck data at the same position as the case of the WMAP data but they do not affect the cosmological parameter estimation significantly.
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The cosmic microwave background (CMB) provides us with a wealth of information about the properties of our Universe. In this PhD work, we develop and apply new techniques for studying fundamental problems of cosmology using the CMB.
Dark energy, if it exists, leaves a characteristic imprint in the CMB temperature fluctuations, the so-called integrated Sachs-Wolfe (ISW) effect. This small effect can be detected via its cross-correlation with the large-scale structure (LSS). We derive an optimal method for ISW detection using temperature and polarization data of the CMB which differs from that usually used in two fundamental ways: we keep the LSS distribution and a part of the
primordial temperature fluctuations fixed, rather than averaging over different realisations as done in the standard method. For an ideal scenario, we obtain an overall enhancement of the detection significance of 23 per cent. For polarization data from the Planck Surveyor mission, this enhancement will be at least 10 per cent, where the limiting factor will be the contamination by Galactic foregrounds.
The CMB is observed to be almost perfectly isotropic, which is considered strong evidence for the isotropy of the
Universe. However, some anomalies have been found in the
temperature map of the Wilkinson Microwave Anisotropy Probe
(WMAP), which seem to question the statistical isotropy of the temperature fluctuations. In order to understand
whether these are due to chance fluctuations or to a preferred direction intrinsic to the geometry of the primordial Universe, we compute the part of the WMAP
polarization map which is uncorrelated with the temperature map, and use it as a statistically independent probe of the so-called axis of evil. The latter is an unusual alignment between the preferred directions of the quadrupole and the octopole in the temperature map. We find that the axis of the quadrupole of the uncorrelated polarization map aligns with the axis of evil, whereas the axis of the octopole does not. However, due to the high noise-level in the WMAP polarization map, we have an uncertainty of about 45 deg in our axes. With this uncertainty, the probability of at least one axis aligning by chance in an isotropic Universe is around 50 per cent. We therefore do not obtain evidence for or against a preferred direction intrinsic to the primordial Universe. For Planck, we expect the uncertainty in the axes to go down to 10-20 deg, again depending on how well the foregrounds can be removed from the map. Our technique applied to Planck data will thus serve as a powerful means to understand the origin of the CMB anomalies.
Instead of studying particular features in the CMB maps as
described above, we can also use the CMB to constrain
several cosmological parameters simultaneously by sampling the parameter space. The parameter constraints obtained by WMAP marked the beginning of precision cosmology and were the biggest success of the mission. In such parameter sampling studies, the main bottleneck is usually the evaluation of the likelihood. We have thus implemented a sparse-grids based interpolation of the WMAP likelihood surface as a shortcut for the likelihood evaluation. This
is orders of magnitude faster to compute than the original likelihood. Our method is a competitive alternative to other approaches for speeding up parameter sampling.
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We present a new method based on phase analysis for the Galaxy and foreground component separation from the cosmic microwave background (CMB) signal. This method is based on a prevailing assumption that the phases of the underlying CMB signal should have no or little correlation with those of the foregrounds. This method takes into consideration all the phases of each multipole mode (l <= 50, -l <= m <=l) from the whole sky without galactic cut, masks or any dissection of the whole sky into disjoint regions. We use cross correlation of the phases to illustrate that significant correlations of the foregrounds manifest themselves in the phases of the WMAP 5 frequency bands, which are used for separation of the CMB from the signals. Our final phase-cleaned CMB map has the angular power spectrum in agreement with both the WMAP result and that from Tegmark, de Oliveira-Costa and Hamilton (TOH), the phases of our derived CMB signal, however, are slightly different from those of the WMAP Internal Linear Combination map and the TOH map.
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We present a new method based on phase analysis for the Galaxy and foreground component separation from the cosmic microwave background (CMB) signal. This method is based on a prevailing assumption that the phases of the underlying CMB signal should have no or little correlation with those of the foregrounds. This method takes into consideration all the phases of each multipole mode (l <= 50, -l <= m <=l) from the whole sky without galactic cut, masks or any dissection of the whole sky into disjoint regions. We use cross correlation of the phases to illustrate that significant correlations of the foregrounds manifest themselves in the phases of the WMAP 5 frequency bands, which are used for separation of the CMB from the signals. Our final phase-cleaned CMB map has the angular power spectrum in agreement with both the WMAP result and that from Tegmark, de Oliveira-Costa and Hamilton (TOH), the phases of our derived CMB signal, however, are slightly different from those of the WMAP Internal Linear Combination map and the TOH map.
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Theoretical Background of the CMB.- Methods for Testing the Non-Gaussianity of the CMB.- Observations of the CMB with the WMAP Satellite.- Scaling Indices Applied to the WMAP 5-Year Data.- Surrogates and Scaling Indices Applied to the WMAP 7-Year Data.- Extending the Analysis of the WMAP 7-Year Data.- Applying the Surrogate Approach to to Incomplete Skies.
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