Non-Gaussian Covariance of CMB B-modes of Polarization and Parameter Degradation

Abstract

The B-mode polarization lensing signal is a useful probe of the neutrino mass and to a lesser extent the dark energy equation of state as the signal depends on the integrated mass power spectrum between us and the last scattering surface. This lensing B-mode signal, however, is non-Gaussian and the resulting non-Gaussian covariance to the power spectrum cannot be ignored as correlations between B-mode bins are at a level of 0.1. For temperature and E-mode polarization power spectra, the non-Gasussian covariance is not significant, where we find correlations at the 10^{-5} level even for adjacent bins. The resulting degradation on neutrino mass and dark energy equation of state is about a factor of 2 to 3 when compared to the case where statistics are simply considered to be Gaussian. We also discuss parameter uncertainties achievable in upcoming experiments and show that at a given angular resolution for polarization observations, increasing the sensitivity beyond a certain noise value does not lead to an improved measurement of the neutrino mass and dark energy equation of state with B-mode power spectrum. For Planck, the resulting constraints on the sum of the neutrino masses is ~ 0.2 eV and on the dark energy equation of state parameter we find, sigma_w ~ 0.5.