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Published June 1, 2023 | public
Journal Article

BICEP/Keck. XVII. Line-of-sight Distortion Analysis: Estimates of Gravitational Lensing, Anisotropic Cosmic Birefringence, Patchy Reionization, and Systematic Errors


We present estimates of line-of-sight distortion fields derived from the 95 and 150 GHz data taken by BICEP2, BICEP3, and the Keck Array up to the 2018 observing season, leading to cosmological constraints and a study of instrumental and astrophysical systematics. Cosmological constraints are derived from three of the distortion fields concerning gravitational lensing from large-scale structure, polarization rotation from magnetic fields or an axion-like field, and the screening effect of patchy reionization. We measure an amplitude of the lensing power spectrum A^(ϕϕ)_(L) = 0.95 ± 0.20. We constrain polarization rotation, expressed as the coupling constant of a Chern–Simons electromagnetic term g_(αγ) ≤ 2.6 × 10⁻²/H_ɪ, where H_ɪ is the inflationary Hubble parameter, and an amplitude of primordial magnetic fields smoothed over 1 Mpc B_(1Mpc) ≤ 6.6 nG at 95 GHz. We constrain the rms of optical depth fluctuations in a simple "crinkly surface" model of patchy reionization, finding A^τ < 0.19 (2σ) for the coherence scale of L_c = 100. We show that all of the distortion fields of the 95 and 150 GHz polarization maps are consistent with simulations including lensed ΛCDM, dust, and noise, with no evidence for instrumental systematics. In some cases, the EB and TB quadratic estimators presented here are more sensitive than our previous map-based null tests at identifying and rejecting spurious B-modes that might arise from instrumental effects. Finally, we verify that the standard deprojection filtering in the BICEP/Keck data processing is effective at removing temperature to polarization leakage.

Additional Information

The BICEP/Keck projects have been made possible through a series of grants from the National Science Foundation, including 0742818, 0742592, 1044978, 1110087, 1145172, 1145143, 1145248, 1639040, 1638957, 1638978, and 1638970, and by the Keck Foundation. The development of antenna-coupled detector technology was supported by the JPL Research and Technology Development Fund and NASA grants 06-ARPA206-0040, 10-SAT10-0017, 12-SAT12-0031, 14-SAT14-0009, and 16-SAT-16-0002. The development and testing of focal planes was supported by the Gordon and Betty Moore Foundation at Caltech. Readout electronics were supported by a Canada Foundation for Innovation grant to UBC. Support for quasi-optical filtering was provided by UK STFC grant ST/N000706/1. The computations in this paper were run on the Odyssey/Cannon cluster supported by the FAS Science Division Research Computing Group at Harvard University. The analysis effort at Stanford and SLAC is partially supported by the U.S. DOE Office of Science. We thank the staff of the U.S. Antarctic Program, in particular the South Pole Station, without whose help this research would not have been possible. Most special thanks go to our heroic winter-overs Robert Schwarz, Steffen Richter, Sam Harrison, Grantland Hall, and Hans Boenish. We thank all of those who have contributed past efforts to the BICEP/Keck series of experiments, including the BICEP1 team. We also thank the Planck and WMAP teams for the use of their data and are grateful to the Planck team for helpful discussions.

Additional details

August 22, 2023
October 20, 2023