A demonstration of improved constraints on primordial gravitational waves with delensing

Abstract

We present a constraint on the tensor-to-scalar ratio, r, derived from measurements of cosmic microwave background (CMB) polarization B-modes with "delensing," whereby the uncertainty on r contributed by the sample variance of the gravitational lensing B-modes is reduced by cross-correlating against a lensing B-mode template. This template is constructed by combining an estimate of the polarized CMB with a tracer of the projected large-scale structure. The large-scale-structure tracer used is a map of the cosmic infrared background derived from Planck satellite data, while the polarized CMB map comes from a combination of South Pole Telescope, BICEP/Keck, and Planck data. We expand the BICEP/Keck likelihood analysis framework to accept a lensing template and apply it to the BICEP/Keck dataset collected through 2014 using the same parametric foreground modeling as in the previous analysis. From simulations, we find that the uncertainty on r is reduced by ∼10%, from σðrÞ ¼ 0.024 to 0.022, which can be compared with a ∼26% reduction obtained when using a perfect lensing template or if there were zero lensing B-modes. Applying the

Improved Constraints on Primordial Gravitational Waves using Planck , WMAP, and BICEP/ Keck Observations through the 2018 Observing Season

“…In addition, we are already in the regime where the sample variance of the lensing component dominates σðrÞ. However, the lensing B modes can be spatially separated from a primordial component and in this regard we have recently demonstrated a path forward by adding a "lensing template" derived from SPTpol and Planck data to the BK14 analysis, resulting in an improved constraint on r [64].…”

The Simons Observatory Large Aperture Telescope Receiver

“…There are even prospects for the LAT to detect Oort clouds around nearby stars (Blake et al 2019;Orlowski-Scherer et al 2019) or additional planets in our solar system (Baxter et al 2018). Finally, observations made with the LAT can be used to delens largescale B-mode signals (Ade et al 2021) measured with the SATs. A complete discussion of the LAT science can be found in the SO forecast paper (The Simons Observatory Collaboration 2019).…”

Snowmass2021 Theory Frontier White Paper: Data-Driven Cosmology

“…In the context of inflation, a detection of primordial B modes would provide evidence for quantum fluctuations in the spacetime metric itself, would imply that inflation took place at energy scales comparable to those associated with grand unified theories, and would imply a Planckian field range, just to mention some of the consequences. Because of these far-reaching implications, several CMB experiments are currently searching for this polarization pattern [16][17][18][19][20][21] and more will begin taking data soon.…”

“…However, since the statistical properties of the CMB are well understood, high-precision measurements of the polarization on scales near the lensing peak can be used to reconstruct the lensing potential, and ultimately to remove the lensing B modes [46][47][48][49]. This has only recently been demonstrated on data [17,[55][56][57][58][59][60], and work is ongoing to develop techniques appropriate for the stringent requirements of future ground-based surveys [61][62][63][64][65]. A key aspect that remains to be better understood is the effect of foregrounds on delensing.…”

“…Major progress on this topic is made by the current (Stage 3) generation of photometric surveys, such as Kilo-Degree Survey (KiDS) [300], the Hyper Suprime Cam (HSC) [301], the Dark Energy Survey (DES) [302] and spectroscopic surveys, such as the Baryon Oscillation Spectroscopic Survey (BOSS) [303]. These low-redshift constraints of the ΛCDM model can be contrasted with CMB measurements from the early Universe made e.g., by the Planck satellite [1], the Atacama Cosmology Telescope (ACT) [304,305], and the South Pole Telescope (SPT) [17].…”