2 research outputs found
CMBPol Mission Concept Study: Gravitational Lensing
Gravitational lensing of the cosmic microwave background by large-scale
structure in the late universe is both a source of cosmological information and
a potential contaminant of primordial gravity waves. Because lensing imprints
growth of structure in the late universe on the CMB, measurements of CMB
lensing will constrain parameters to which the CMB would not otherwise be
sensitive, such as neutrino mass.
If the instrumental noise is sufficiently small (<~ 5 uK-arcmin), the
gravitational lensing contribution to the large-scale B-mode will be the
limiting source of contamination when constraining a stochastic background of
gravity waves in the early universe, one of the most exciting prospects for
future CMB polarization experiments. High-sensitivity measurements of
small-scale B-modes can reduce this contamination through a lens reconstruction
technique that separates the lensing and primordial contributions to the B-mode
on large scales.
A fundamental design decision for a future CMB polarization experiment such
as CMBpol is whether to have coarse angular resolution so that only the
large-scale B-mode (and the large-scale E-mode from reionization) is measured,
or high resolution to additionally measure CMB lensing. The purpose of this
white paper is to evaluate the science case for CMB lensing in polarization:
constraints on cosmological parameters, increased sensitivity to the gravity
wave B-mode via lens reconstruction, expected level of contamination from
non-CMB foregrounds, and required control of beam systematics
Gravitational Lensing
Gravitational lensing of the cosmic microwave background by largeāscale structure in the late universe is both a source of cosmological information and a potential contaminant of primordial gravity waves. Because lensing imprints growth of structure in the late universe on the CMB, measurements of CMB lensing will constrain parameters to which the CMB would not otherwise be sensitive, such as neutrino mass.
In CMB polarization, gravitational lensing is the largest guaranteed source of Bāmode (or curlālike) polarization. Future CMB polarization experiments with sufficient sensitivity to measure Bāmodes on small angular scales (l ā¼ 1000) can measure lensing with better sensitivity, and on different scales, than could be achieved by measuring CMB temperature alone. If the instrumental noise is sufficiently small (ā² 5 Ī¼Kāarcmin), the gravitational lensing contribution to the largeāscale Bāmode will be the limiting source of contamination when constraining a stochastic background of gravity waves in the early universe, one of the most exciting prospects for future CMB polarization experiments. Highāsensitivity measurements of smallāscale Bāmodes can reduce this contamination through a lens reconstruction technique that separates the lensing and primordial contributions to the Bāmode on large scales.
A fundamental design decision for a future CMB polarization experiment such as CMBpol is whether to have coarse angular resolution so that only the largeāscale Bāmode (and the largeāscale Eāmode from reionization) is measured, or high resolution to additionally measure CMB lensing. The purpose of this white paper is to evaluate the science case for CMB lensing in polarization: constraints on cosmological parameters, increased sensitivity to the gravity wave Bāmode via lens reconstruction, expected level of contamination from nonāCMB foregrounds, and required control of beam systematics