CMB-S4: Forecasting Constraints on Primordial Gravitational Waves

Kevork Abazajian, Graeme E. Addison, Peter Adshead, Zeeshan Ahmed, Daniel Akerib, Aamir Ali, Steven W. Allen, David Alonso, Marcelo Alvarez, Mustafa A. Amin, Adam Anderson, Kam S. Arnold, Peter Ashton, Carlo Baccigalupi, Debbie Bard, Denis Barkats, Darcy Barron, Peter S. Barry, James G. Bartlett, Ritoban Basu ThakurNicholas Battaglia, Rachel Bean, Chris Bebek, Amy N. Bender, Bradford A. Benson, Federico Bianchini, Colin A. Bischoff, Lindsey Bleem, James J. Bock, Sebastian Bocquet, Kimberly K. Boddy, J. Richard Bond, Julian Borrill, François R. Bouchet, Thejs Brinckmann, Michael L. Brown, Sean Bryan, Victor Buza, Karen Byrum, Carlos Hervias Caimapo, Erminia Calabrese, Victoria Calafut, Robert Caldwell, John E. Carlstrom, Julien Carron, Thomas Cecil, Anthony Challinor, Clarence L. Chang, Yuji Chinone, Hsiao Mei Sherry Cho, Asantha Cooray, Will Coulton, Thomas M. Crawford, Abigail Crites, Ari Cukierman, Francis Yan Cyr-Racine, Tijmen De Haan, Jacques Delabrouille, Mark Devlin, Eleonora Di Valentino, Marion Dierickx, Matt Dobbs, Shannon Duff, Cora Dvorkin, Joseph Eimer, Tucker Elleflot, Josquin Errard, Thomas Essinger-Hileman, Giulio Fabbian, Chang Feng, Simone Ferraro, Jeffrey P. Filippini, Raphael Flauger, Brenna Flaugher, Aurelien A. Fraisse, Andrei Frolov, Nicholas Galitzki, Patricio A. Gallardo, Silvia Galli, Ken Ganga, Martina Gerbino, Vera Gluscevic, Neil Goeckner-Wald, Daniel Green, Daniel Grin, Evan Grohs, Riccardo Gualtieri, Jon E. Gudmundsson, Ian Gullett, Nikhel Gupta, Salman Habib, Mark Halpern, Nils W. Halverson, Shaul Hanany, Kathleen Harrington, Masaya Hasegawa, Matthew Hasselfield, Masashi Hazumi, Katrin Heitmann, Shawn Henderson, Brandon Hensley, Charles Hill, J. Colin Hill, Renée Hlozek, Shuay Pwu Patty Ho, Thuong Hoang, Gil Holder, William Holzapfel, John Hood, Johannes Hubmayr, Kevin M. Huffenberger, Howard Hui, Kent Irwin, Oliver Jeong, Bradley R. Johnson, William C. Jones, Jae Hwan Kang, Kirit S. Karkare, Nobuhiko Katayama, Reijo Keskitalo, Theodore Kisner, Lloyd Knox, Brian J. Koopman, Arthur Kosowsky, John Kovac, Ely D. Kovetz, Steve Kuhlmann, Chao Lin Kuo, Akito Kusaka, Anne Lähteenmäki, Charles R. Lawrence, Adrian T. Lee, Antony Lewis, Dale Li, Eric Linder, Marilena Loverde, Amy Lowitz, Phil Lubin, Mathew S. Madhavacheril, Adam Mantz, Gabriela Marques, Frederick Matsuda, Philip Mauskopf, Heather McCarrick, Jeffrey McMahon, P. Daniel Meerburg, Jean Baptiste Melin, Felipe Menanteau, Joel Meyers, Marius Millea, Joseph Mohr, Lorenzo Moncelsi, Maria Monzani, Tony Mroczkowski, Suvodip Mukherjee, Johanna Nagy, Toshiya Namikawa, Federico Nati, Tyler Natoli, Laura Newburgh, Michael D. Niemack, Haruki Nishino, Brian Nord, Valentine Novosad, Roger O'Brient, Stephen Padin, Steven Palladino, Bruce Partridge, Don Petravick, Elena Pierpaoli, Levon Pogosian, Karthik Prabhu, Clement Pryke, Giuseppe Puglisi, Benjamin Racine, Alexandra Rahlin, Mayuri Sathyanarayana Rao, Marco Raveri, Christian L. Reichardt, Mathieu Remazeilles, Graca Rocha, Natalie A. Roe, Anirban Roy, John E. Ruhl, Maria Salatino, Benjamin Saliwanchik, Emmanuel Schaan, Alessandro Schillaci, Benjamin Schmitt, Marcel M. Schmittfull, Douglas Scott, Neelima Sehgal, Sarah Shandera, Blake D. Sherwin, Erik Shirokoff, Sara M. Simon, Anze Slosar, David Spergel, Tyler St. Germaine, Suzanne T. Staggs, Antony Stark, Glenn D. Starkman, Radek Stompor, Chris Stoughton, Aritoki Suzuki, Osamu Tajima, Grant P. Teply, Keith Thompson, Ben Thorne, Peter Timbie, Maurizio Tomasi, Matthieu Tristram, Gregory Tucker, Caterina Umiltà, Alexander Van Engelen, Eve M. Vavagiakis, Joaquin D. Vieira, Abigail G. Vieregg, Kasey Wagoner, Benjamin Wallisch, Gensheng Wang, Scott Watson, Ben Westbrook, Nathan Whitehorn, Edward J. Wollack, W. L. Kimmy Wu, Zhilei Xu, H. Y. Eric Yang, Siavash Yasini, Volodymyr G. Yefremenko, Ki Won Yoon, Edward Young, Cyndia Yu, Andrea Zonca

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8 Scopus citations


CMB-S4 - the next-generation ground-based cosmic microwave background (CMB) experiment - is set to significantly advance the sensitivity of CMB measurements and enhance our understanding of the origin and evolution of the universe. Among the science cases pursued with CMB-S4, the quest for detecting primordial gravitational waves is a central driver of the experimental design. This work details the development of a forecasting framework that includes a power-spectrum-based semianalytic projection tool, targeted explicitly toward optimizing constraints on the tensor-to-scalar ratio, r, in the presence of Galactic foregrounds and gravitational lensing of the CMB. This framework is unique in its direct use of information from the achieved performance of current Stage 2-3 CMB experiments to robustly forecast the science reach of upcoming CMB-polarization endeavors. The methodology allows for rapid iteration over experimental configurations and offers a flexible way to optimize the design of future experiments, given a desired scientific goal. To form a closed-loop process, we couple this semianalytic tool with map-based validation studies, which allow for the injection of additional complexity and verification of our forecasts with several independent analysis methods. We document multiple rounds of forecasts for CMB-S4 using this process and the resulting establishment of the current reference design of the primordial gravitational-wave component of the Stage-4 experiment, optimized to achieve our science goals of detecting primordial gravitational waves for r > 0.003 at greater than 5σ, or in the absence of a detection, of reaching an upper limit of r < 0.001 at 95% CL.

Original languageEnglish (US)
Article number54
JournalAstrophysical Journal
Issue number1
StatePublished - Feb 1 2022

Bibliographical note

Funding Information:
The CMB-S4 collaboration ( ) is working to plan, construct, and operate a next-generation, multisite CMB experiment in the 2020s. The collaboration is led by an elected Governing Board, Spokespeople, Committee Chairs, and Executive Team. Funding for the CMB-S4 Integrated Project Office is provided by the Department of Energy’s Office of Science (project level CD-0) and by the National Science Foundation through the Mid-Scale Research Infrastructure-R1 award OPP-1935892. This research used resources of Argonne National Laboratory, a U.S. Department of Energy (DOE) Office of Science User Facility operated under Contract No. DE-AC02-06CH11357. This document was prepared by the CMB-S4 collaboration using the resources of the Fermi National Accelerator Laboratory (Fermilab), a U.S. Department of Energy, Office of Science, HEP User Facility. Fermilab is managed by Fermi Research Alliance, LLC (FRA), acting under Contract No. DE-AC02-07CH11359. Work at Lawrence Berkeley National Laboratory was supported by the Office of Science, Office of Basic Energy Sciences, of the U.S. Department of Energy under Contract No. DE-AC02-05CH11231. Work at SLAC National Accelerator Laboratory is supported by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences under Contract No. DE-AC02-76SF00515. This research used resources of the National Energy Research Scientific Computing Center, which is supported by the Office of Science of the U.S. Department of Energy under Contract No. DE-AC02-05CH11231. In the United States, work on CMB-S4 by individual investigators has been supported by the National Science Foundation (awards 1248097, 1255358, 1815887, 1835865, 1852617, 2009469), the Department of Energy (awards DE-SC0009919, DE-SC0009946, DE-SC0010129, DE-SC0011784), and the National Aeronautics and Space Administration (award ATP-80NSSC20K0518). In Australia, the Melbourne authors acknowledge support from an Australian Research Council Future Fellowship (FT150100074). In Canada, R.H. is supported by the Discovery Grants program from NSERC, and acknowledges funding from CIFAR, the Sloan Foundation, and the Dunlap family. In Italy, C.B. acknowledges support under the ASI COSMOS and INFN INDARK programs. In the Netherlands, D.M. acknowledges NWO VIDI award number 639.042.730. In Switzerland, J.C. is supported by an SNSF Eccellenza Professorial Fellowship (No. 186879). In the United Kingdom, A.L., G.F., and J.C. are supported by the European Research Council under the European Union’s Seventh Framework Programme (FP/2007-2013)/ERC grant Agreement No. [616170]. A.L. also acknowledges STFC award ST/P000525/1. S.M. is supported by the research program Innovational Research Incentives Scheme (Vernieuwingsimpuls), which is financed by the Netherlands Organization for Scientific Research through the NWO VIDI grant No. 639.042.612-Nissanke and the Labex ILP (reference ANR-10-LABX-63) part of the Idex SUPER, received financial state aid managed by the Agence Nationale de la Recherche, as part of the program Investissements d’avenir under the reference ANR-11-IDEX-0004-02. Some computations in this paper were run on the Odyssey cluster, supported by the FAS Science Division Research Computing Group at Harvard University.

Publisher Copyright:
© 2022. The Author(s). Published by the American Astronomical Society.


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