BICEP/Keck Collaboration, SPTpol Collaboration, Ade, P. A. R., Ahmed, Z., Amiri, M., Anderson, A. J., Austermann, J. E., Avva, J. S., Barkats, Denis, Thakur, R. Basu, Beall, J. A., Bender, A. N., Benson, B. A., Bianchini, F., Bischoff, C. A., Bleem, L. E., Bock, J. J., Boenish, H., Bullock, E., Buza, Victor, Carlstrom, J. E., Chang, C. L., Cheshire, J. R., Chiang, H. C., Chou, T. -L et al. 2021. "A demonstration of improved constraints on primordial gravitational waves with delensing." Physical Review D, 103 022004. https://doi.org/10.1103/PhysRevD.103.022004.
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 σ (r )=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 technique to the real data, the constraint on r is improved from r0.050.05<0.082 (95% C.L.). This is the first demonstration of improvement in an r constraint through delensing.
