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arXiv · 2603.06812

BICEP/Keck XXI: Constraints on Early-Universe Parity Violation from Multipole-Dependent Birefringence

Keck Collaboration·P. A. R. Ade·Zeeshan Ahmed·Mandana Amiri·Denis Barkats·Ritoban Basu Thakur·Colin A. Bischoff·Dominic Beck·James J. Bock·Hans Boenish·Victor Buza·Brianna Cantrall·James R. Cheshire IV·Jake Connors·James Cornelison·Michael Crumrine·Ari Jozef Cukierman·Edward Denison·Lionel Duband·Michael Echter·Miranda Eiben·Brodi D. Elwood·Sofia Fatigoni·Jeffrey P. Filippini·Antonio Fortes·Min Gao·Christos Giannakopoulos·Neil Goeckner-Wald·David C. Goldfinger·Stephen Gratton·James A. Grayson·Annsley Greathouse·Paul K. Grimes·Grantland Hall·George Halal·Mark Halpern·Emma Hand·Sam A. Harrison·Shawn Henderson·Thuong Hoang·Johannes Hubmayr·Howard Hui·Kent D. Irwin·Jae Hwan Kang·Kirit S. Karkare·Sinan Kefeli·J. M. Kovac·Chao-Lin Kuo·Kekoa Lasko·King Lau·Margaret Lautzenhiser·Amber Lennox·Tongtian Liu·Scott Mackey·Nolan Maher·Koko G. Megerian·Lorenzo Minutolo·Lorenzo Moncelsi·Yuka Nakato·H. T. Nguyen·Roger O'Brient·Scott Paine·Anika Patel·Matthew A. Petroff·Anna R. Polish·Thomas Prouve·Clement Pryke·Carl D. Reintsema·Steffen Richter·Thibault Romand·Maria Salatino·Alessandro Schillaci·Benjamin Schmitt·Robert Schwarz·Chris D. Sheehy·Baibhav Singari·Ahmed Soliman·Tyler St Germaine·Aaron Steiger·Bryan Steinbach·Rashmi Sudiwala·Grant Teply·Keith L. Thompson·Carole Tucker·Anthony D. Turner·Clara Vergès·Abigail G. Vieregg·Albert Wandui·Alexis C. Weber·Justin Willmert·Chin Lin Wong·Wai Ling K. Wu·Hung-I Yang·Cyndia Yu·Lingzhen Zeng·Cheng Zhang·Silvia Zhang
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Abstract

We present the first constraints on multipole-dependent cosmic birefringence using CMB polarization data from the BK18 dataset, which combines observations from BICEP2, Keck Array, and BICEP3 at frequencies of 95, 150, and 220 GHz. Photon coupling to an axion-like field leads to the rotation of CMB polarization, inducing non-zero EB cross-correlations. We show that a multipole-dependent rotation beta(l) imprints a distinct signature in the polarization spectra that can be constrained. Specifically, we consider an Early Dark Energy (EDE) scenario in which a pseudoscalar field couples to photons through a Chern-Simons interaction, generating a polarization rotation with multipole dependence. We introduce a phenomenological beta(l) as a step function, obtaining constraints on the step function size consistent with zero, with uncertainties less than 0.15 degrees (68% CL). In addition, using multi-frequency EE, BB, and EB cross-spectra, along with robust BICEP/Keck foreground treatment and likelihood framework, we derive constraints on the axion-photon coupling amplitude g for several choices of EDE parameters. For the baseline best-fit value f_{EDE} = 0.087 from the Planck 2018 analysis, we obtain g = 0.11 +/- 0.37 (68% CL), consistent with previous limits.

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Keck Collaboration, P. A. R. Ade, Zeeshan Ahmed, Mandana Amiri, Denis Barkats, Ritoban Basu Thakur, Colin A. Bischoff, Dominic Beck, James J. Bock, Hans Boenish, Victor Buza, Brianna Cantrall, James R. Cheshire IV, Jake Connors, James Cornelison, Michael Crumrine, Ari Jozef Cukierman, Edward Denison, Lionel Duband, Michael Echter, Miranda Eiben, Brodi D. Elwood, Sofia Fatigoni, Jeffrey P. Filippini, Antonio Fortes, Min Gao, Christos Giannakopoulos, Neil Goeckner-Wald, David C. Goldfinger, Stephen Gratton, James A. Grayson, Annsley Greathouse, Paul K. Grimes, Grantland Hall, George Halal, Mark Halpern, Emma Hand, Sam A. Harrison, Shawn Henderson, Thuong Hoang, Johannes Hubmayr, Howard Hui, Kent D. Irwin, Jae Hwan Kang, Kirit S. Karkare, Sinan Kefeli, J. M. Kovac, Chao-Lin Kuo, Kekoa Lasko, King Lau, Margaret Lautzenhiser, Amber Lennox, Tongtian Liu, Scott Mackey, Nolan Maher, Koko G. Megerian, Lorenzo Minutolo, Lorenzo Moncelsi, Yuka Nakato, H. T. Nguyen, Roger O'Brient, Scott Paine, Anika Patel, Matthew A. Petroff, Anna R. Polish, Thomas Prouve, Clement Pryke, Carl D. Reintsema, Steffen Richter, Thibault Romand, Maria Salatino, Alessandro Schillaci, Benjamin Schmitt, Robert Schwarz, Chris D. Sheehy, Baibhav Singari, Ahmed Soliman, Tyler St Germaine, Aaron Steiger, Bryan Steinbach, Rashmi Sudiwala, Grant Teply, Keith L. Thompson, Carole Tucker, Anthony D. Turner, Clara Vergès, Abigail G. Vieregg, Albert Wandui, Alexis C. Weber, Justin Willmert, Chin Lin Wong, Wai Ling K. Wu, Hung-I Yang, Cyndia Yu, Lingzhen Zeng, Cheng Zhang, Silvia Zhang. 2026-03-06. BICEP/Keck XXI: Constraints on Early-Universe Parity Violation from Multipole-Dependent Birefringence. https://doi.org/10.1103/v8y3-m75b

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