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Large-scale cosmic microwave background temperature and polarization cross-spectra likelihoods

Abstract : One of the main challenges left for the present and future Cosmic Microwave Background (CMB) experiments is the high precision measurement of the CMB polarization anisotropies at large angular scales. The reionization bump in the CMB polarization power spectra encodes unique informations about the reionization history of the Universe and the inflationary epoch. Such valuable information can be accessed only with an unprecedented accuracy and care on each step of the data analysis and its interpretation. In this paper we present a cross-spectra based approach for the analysis of the CMB data at large angular scales to constrain the reionization optical depth, the tensor to scalar ratio and the amplitude of the primordial scalar perturbations. Using cross-spectra has the advantage to eliminate spurious noise bias and to give a better handle of residual systematics with respect to the pixel-based approach used so far, allowing to efficiently combine the cosmological information encoded in cross-frequency or cross-dataset spectra. We present two solutions to deal with the non-Gaussianity of the Cl estimator distributions at large angular scales: the first relies on an analytical parametrization of the estimator distribution, while the second is based on modification of the Hamimache&Lewis likelihood approximation at large angular scales. The modified HL method (oHL) is extremely powerful as it allows to easily deal with multipole and mode correlations for a combined temperature and polarization analysis. We validate our methods on realistic simulations generated with publicly available specifications, showing that they give consistent results for the constraints of the relevant cosmological parameters in the case of a realistic experimental settings that account for anisotropic correlated noise and incomplete sky coverage.
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Contributor : Sabine Starita <>
Submitted on : Thursday, March 5, 2015 - 10:14:11 AM
Last modification on : Friday, December 18, 2020 - 11:20:03 AM

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A. Mangilli, Stéphane Plaszczynski, M. Tristram. Large-scale cosmic microwave background temperature and polarization cross-spectra likelihoods. Monthly Notices of the Royal Astronomical Society, Oxford University Press (OUP): Policy P - Oxford Open Option A, 2015, 453 (3), pp.3174-3189. ⟨10.1093/mnras/stv1733⟩. ⟨in2p3-01123544⟩



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