paper

Towards ending the partial sky E-B ambiguity in CMB observations

arXiv:2007.09928 · doi:10.1088/1475-7516/2021/02/036

Abstract

A crucial problem for partial sky analysis of CMB polarization is the - leakage problem. Such leakage arises from the presence of `ambiguous' modes that satisfy properties of both and modes. Solving this problem is critical for primordial polarization mode detection in partial sky CMB polarization experiments. In this work we introduce a new method for reducing the leakage. We demonstrate that if we complement the -mode information outside the observation patch with ancillary data from full-sky CMB observations, we can reduce and even effectively remove the -to- leakage. For this objective, we produce -mode Stokes maps from Wiener filtered full-sky intensity and polarization CMB observations. We use these maps to fill the sky region that is not observed by the ground-based experiment of interest, and thus complement the partial sky Stokes maps. Since the -mode information is now available on the full sky we see a significant reduction in the -to- leakage. We evaluate on simulated data sets the performance of our method for a `shallow' , and a `deep' northern hemisphere sky patch, with AliCPT-like properties, and a LSPE-like sky patch, by combining those observations with Planck-like full sky polarization maps. We find that our method outperforms the standard and the pure- method pseudo- estimators for all of our simulations. Our new method gives unbiased estimates of the -mode power spectrum through-out the entire multipole range with near-optimal pseudo- errors for . We also study the application of our method to the CMB-S4 experiment combined with LiteBIRD-like full sky data, and show that using signal-dominated full sky -mode data we can eliminate the -to- leakage problem.

arXiv comment24 pages and 15 figures. Comments are welcome

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