Simons Observatory: Constraining inflationary gravitational waves with multitracer B -mode delensing

Toshiya Namikawa, Anton Baleato Lizancos, Naomi Robertson, Blake D. Sherwin, Anthony Challinor, David Alonso, Susanna Azzoni, Carlo Baccigalupi, Erminia Calabrese, Julien Carron, Yuji Chinone, Jens Chluba, Gabriele Coppi, Josquin Errard, Giulio Fabbian, Simone Ferraro, Alba Kalaja, Antony Lewis, Mathew S. Madhavacheril, P. Daniel MeerburgJoel Meyers, Federico Nati, Giorgio Orlando, Davide Poletti, Giuseppe Puglisi, Mathieu Remazeilles, Neelima Sehgal, Osamu Tajima, Grant Teply, Alexander Van Engelen, Edward J. Wollack, Zhilei Xu, Byeonghee Yu, Ningfeng Zhu, Andrea Zonca

Research output: Contribution to journalArticlepeer-review

14 Scopus citations


We introduce and validate a delensing framework for the Simons Observatory (SO), which will be used to improve constraints on inflationary gravitational waves by reducing the lensing noise in measurements of the B modes in CMB polarization. SO will initially observe CMB by using three small aperture telescopes and one large-aperture telescope. While polarization maps from small-aperture telescopes will be used to constrain inflationary gravitational waves, the internal CMB lensing maps used to delens will be reconstructed from data from the large-aperture telescope. Since lensing maps obtained from the SO data will be noise dominated on subdegree scales, the SO lensing framework constructs a template for lensing-induced B modes by combining internal CMB lensing maps with maps of the cosmic infrared background from Planck as well as galaxy density maps from the LSST survey. We construct a likelihood for constraining the tensor-to-scalar ratio r that contains auto and cross spectra between observed B modes and the lensing B-mode template. We test our delensing analysis pipeline on map-based simulations containing survey nonidealities, but that, for this initial exploration, does not include contamination from Galactic and extragalactic foregrounds. We find that the SO survey masking and inhomogeneous and atmospheric noise have very little impact on the delensing performance, and the r constraint becomes σ(r)≈0.0015 which is close to that obtained from the idealized forecasts in the absence of the Galactic foreground and is nearly a factor of 2 tighter than without delensing. We also find that uncertainties in the external large-scale structure tracers used in our multitracer delensing pipeline lead to bias much smaller than the 1σ statistical uncertainties.

Original languageEnglish (US)
Article number023511
JournalPhysical Review D
Issue number2
StatePublished - Jan 15 2022

ASJC Scopus subject areas

  • Nuclear and High Energy Physics


Dive into the research topics of 'Simons Observatory: Constraining inflationary gravitational waves with multitracer B -mode delensing'. Together they form a unique fingerprint.

Cite this