Gravitational lensing as a contaminant of the gravity wave signal in the CMB

By Uros Seljak, C. Hirata. 2003

187 citations recorded by the source corpus.

Gravity waves (GWs) in the early Universe generate B-type polarization in the cosmic microwave background (CMB), which can be used as a direct way to measure the energy scale of inflation. Gravitational lensing contaminates the GW signal by converting the dominant E polarization into B polarization. By reconstructing the lensing potential from the CMB itself one can decontaminate the B mode induced by lensing. We present results of numerical simulations of B mode delensing using quadratic and iterative maximum-likelihood lensing reconstruction methods as a function of detector noise and beam. In our simulations we find that the quadratic method can reduce the lensing B noise power by up to a factor of 7, close to the no noise limit. In contrast, the iterative method shows significant improvements even at the lowest noise levels we tested. We demonstrate explicitly that with this method at least a factor of 40 noise power reduction in lensing induced B power is possible, suggesting that ${r=P}_{h}{/P}_{R}\ensuremath{\sim}{10}^{\ensuremath{-}6}$ may be achievable in the absence of sky cuts, foregrounds, and instrumental systematics. While we do not find any fundamental lower limit due to lensing, we find that for high-sensitivity detectors residual lensing noise dominates over the detector noise.

Subfields: Astronomy and Astrophysics

View Paper: https://www.semanticscholar.org/paper/63ab6cd10bd2ef07f8382d6dc5749f82da37c316

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Citations in the corpus

The Simons Observatory: science goals and forecasts (2018, background): “…B-modes limit the measurement of the tensor-to-scalar ratio, r. Fortunately, given an estimate of the particular realization of the CMB lensing potential in a given patch of sky, it is possible to partially undo the effect of lensing on CMB maps (Knox and Song 2002; Seljak and Hirata 2004).”
Robust forecasts on fundamental physics from the foreground-obscured, gravitationally-lensed CMB polarization (2015, background): “In the limit of noiseless polarization measurements perfect delensing should be possible [29]; in the cases considered here, up to around 80% of the lensing B modes can be removed by the combination of the ground-based Stage-IV and any satellite, assuming polarized dust and synchrotron have previous”
SPT-3G: a next-generation cosmic microwave background polarization experiment on the South Pole telescope (2014, methodology): “Combined with spt-3g’s exquisite E-mode measurement, the lensing B mode measurement will allow delensing of the primordial gravitational-wave B-mode signal with a factor of 4 reduction in power.(33) This delensing ability will enhance spt-3g’s own constraint on r and naturally complement the keck pr”
Neutrino Physics from the Cosmic Microwave Background and Large-Scale Structure (2013, background): “ the lensing Bmodes from the in ationary signal also places stringent requirements on sensitivity. Signicant delensing is only possible with a <100beam and <5 K-arcmin noise in the B-mode map [80]. This noise level and resolution across a signicant area of sky (at least 1000 deg2) would reduce”
PICO: Probe of Inflation and Cosmic Origins (2019, background): “For lower levels of r, the lensing B-mode dominates, but the B-mode maps can be ‘delensed’ if the polarization maps are measured with few-arcmin resolution and sufficient depth [39, 40].”