<i>B</i>-mode constraints from <i>Planck</i> low-multipole polarization data

ABSTRACT We present constraints on primordial B modes from large-angular scale cosmic microwave background polarization anisotropies measured with the Planck satellite. To remove Galactic polarized foregrounds, we use a Bayesian parametric component separation method, modelling synchrotron radiation as power law and thermal dust emission modified blackbody. This method propagates uncertainties foreground cleaning into noise covariance matrices of maps. construct two likelihoods: (i) semi-analytical cross-spectrum-based likelihood-approximation scheme (momento), (ii) an exact polarization-only pixel-based likelihood (pixLike). Since momento is based cross-spectra, it statistically less powerful than pixLike, but sensitive to systematic errors correlated across frequencies. Both likelihoods give tensor-to-scalar ratio, r, that consistent zero low-multipole (2 ≤ ℓ &amp;lt; 30) Planckpolarization data. From full-mission maps, obtain r0.05 0.274 at 95 per cent confidence pivot k* ≡ 0.05 Mpc−1, using pixLike. gives qualitatively similar weaker limit 0.408.