BICEP/ Keck XXI: Constraints on early-Universe parity violation from multipole-dependent birefringence

Le résumé fourni par la source

We present the first constraints on multipole-dependent cosmic birefringence using CMB polarization data from the BK18 dataset, which combines observations from BICEP2, Array, and BICEP3 at frequencies of 95, 150, and 220 GHz. Photon coupling to an axionlike field leads to the rotation of CMB polarization, inducing nonzero E B cross-correlations. We show that a multipole-dependent rotation β ( 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 β ( ℓ ) as a step function, obtaining constraints on the step function size consistent with zero, with uncertainties less than ∼ 0.15 ° (68% CL). In addition, using multi-frequency E E , B B , and E B cross spectra, along with robust BICEP/ 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 2018 analysis, we obtain g = 0.11 ± 0.37 (68% CL), consistent with previous limits.

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