Exploring cosmic origins with CORE: Gravitational lensing of the CMB
2018
Lensing of the cosmic microwave background (CMB) is now a well-developed
probe of the clustering of the large-scale mass distribution over a broad range of redshifts.
By exploiting the non-Gaussian imprints of lensing in the polarization of the CMB, the
CORE mission will allow production of a clean map of the lensing de
ections over nearly the
full-sky. The number of high-S=N modes in this map will exceed current CMB lensing maps
by a factor of 40, and the measurement will be sample-variance limited on all scales where
linear theory is valid. Here, we summarise this mission product and discuss the science
that will follow from its power spectrum and the cross-correlation with other clustering
data. For example, the summed mass of neutrinos will be determined to an accuracy of
17meV combining CORE lensing and CMB two-point information with contemporaneous
measurements of the baryon acoustic oscillation feature in the clustering of galaxies, three
times smaller than the minimum total mass allowed by neutrino oscillation measurements.
Lensing has applications across many other science goals of CORE, including the search for
B-mode polarization from primordial gravitational waves. Here, lens-induced B-modes will
dominate over instrument noise, limiting constraints on the power spectrum amplitude of
primordial gravitational waves. With lensing reconstructed by CORE, one can delens" the
observed polarization internally, reducing the lensing B-mode power by 60 %. This can be
improved to 70% by combining lensing and measurements of the cosmic infrared background
from CORE, leading to an improvement of a factor of 2:5 in the error on the amplitude
of primordial gravitational waves compared to no delensing (in the null hypothesis of no
primordial B-modes). Lensing measurements from CORE will allow calibration of the halo
masses of the tens of thousands of galaxy clusters that it will find, with constraints dominated
by the clean polarization-based estimators. The 19 frequency channels proposed for CORE
will allow accurate removal of Galactic emission from CMB maps. We present initial findings
that show that residual Galactic foreground contamination will not be a significant source of
bias for lensing power spectrum measurements with CORE.
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