BICEP/Keck XXI: Constraints on Early-Universe Parity Violation from Multipole-Dependent Birefringence
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.
Keywords
Cite
@article{arxiv.2603.06812,
title = {BICEP/Keck XXI: Constraints on Early-Universe Parity Violation from Multipole-Dependent Birefringence},
author = {Keck Collaboration and P. A. R. Ade and Zeeshan Ahmed and Mandana Amiri and Denis Barkats and Ritoban Basu Thakur and Colin A. Bischoff and Dominic Beck and James J. Bock and Hans Boenish and Victor Buza and Brianna Cantrall and James R. Cheshire and Jake Connors and James Cornelison and Michael Crumrine and Ari Jozef Cukierman and Edward Denison and Lionel Duband and Michael Echter and Miranda Eiben and Brodi D. Elwood and Sofia Fatigoni and Jeffrey P. Filippini and Antonio Fortes and Min Gao and Christos Giannakopoulos and Neil Goeckner-Wald and David C. Goldfinger and Stephen Gratton and James A. Grayson and Annsley Greathouse and Paul K. Grimes and Grantland Hall and George Halal and Mark Halpern and Emma Hand and Sam A. Harrison and Shawn Henderson and Thuong Hoang and Johannes Hubmayr and Howard Hui and Kent D. Irwin and Jae Hwan Kang and Kirit S. Karkare and Sinan Kefeli and J. M. Kovac and Chao-Lin Kuo and Kekoa Lasko and King Lau and Margaret Lautzenhiser and Amber Lennox and Tongtian Liu and Scott Mackey and Nolan Maher and Koko G. Megerian and Lorenzo Minutolo and Lorenzo Moncelsi and Yuka Nakato and H. T. Nguyen and Roger O'Brient and Scott Paine and Anika Patel and Matthew A. Petroff and Anna R. Polish and Thomas Prouve and Clement Pryke and Carl D. Reintsema and Steffen Richter and Thibault Romand and Maria Salatino and Alessandro Schillaci and Benjamin Schmitt and Robert Schwarz and Chris D. Sheehy and Baibhav Singari and Ahmed Soliman and Tyler St Germaine and Aaron Steiger and Bryan Steinbach and Rashmi Sudiwala and Grant Teply and Keith L. Thompson and Carole Tucker and Anthony D. Turner and Clara Vergès and Abigail G. Vieregg and Albert Wandui and Alexis C. Weber and Justin Willmert and Chin Lin Wong and Wai Ling K. Wu and Hung-I Yang and Cyndia Yu and Lingzhen Zeng and Cheng Zhang and Silvia Zhang},
journal= {arXiv preprint arXiv:2603.06812},
year = {2026}
}
Comments
19 pages, 9 figures, 9 tables