Cosmological information from lensed CMB power spectra

Abstract

Gravitational lensing distorts the cosmic microwave background (CMB) temperature and polarization fields and encodes valuable information on distances and growth rates at intermediate redshifts into the lensed power spectra. The non-Gaussian band-power covariance induced by the lenses is negligible to $l=2000$ for all but the $B$ polarization field where it increases the net variance by up to a factor of 10 and favors an observing strategy with 3 times more area than if it were Gaussian. To quantify the cosmological information, we introduce two lensing observables, characterizing nearly all of the information, which simplify the study of non-Gaussian impact, parameter degeneracies, dark energy models, and complementarity with other cosmological probes. Information on the intermediate-redshift parameters rapidly becomes limited by constraints on the cold dark matter density and initial amplitude of fluctuations as observations improve. Extraction of this information requires deep polarization measurements on only 5%–10% of the sky, and can improve Planck lensing constraints by a factor of $\sim 2–3$ on any one of the parameters $\{w_0,w_a,{\Omega }_K,\sum _{}^{}{m}_{\nu }\}$ with the others fixed. Sensitivity to the curvature and neutrino mass is the highest due to the high-redshift weight of CMB lensing but degeneracies between the parameters must be broken externally.