Constraints on ΛCDM extensions from the SPT-3G 2018 EE and TE power spectra

Abstract

We present constraints on extensions to the ΛCDM cosmological model from measurements of the E-mode polarization autopower spectrum and the temperature-E-mode cross-power spectrum of the cosmic microwave background (CMB) made using 2018 SPT-3G data. The extensions considered vary the primordial helium abundance, the effective number of relativistic degrees of freedom, the sum of neutrino masses, the relativistic energy density and mass of a sterile neutrino, and the mean spatial curvature. We do not find clear evidence for any of these extensions, from either the SPT-3G 2018 dataset alone or in combination with baryon acoustic oscillation and Planck data. None of these model extensions significantly relax the tension between Hubble-constant, H₀, constraints from the CMB and from distance-ladder measurements using Cepheids and supernovae. The addition of the SPT-3G 2018 data to Planck reduces the square-root of the determinants of the parameter covariance matrices by factors of 1.3–2.0 across these models, signaling a substantial reduction in the allowed parameter volume. We also explore CMB-based constraints on H₀ from combined SPT, Planck, and ACT DR4 datasets. While individual experiments see some indications of different H₀ values between the TT, TE, and EE spectra, the combined H₀ constraints are consistent between the three spectra. For the full combined datasets, we report H₀ = 67.49±0.53  km s⁻¹ Mpc⁻¹, which is the tightest constraint on H₀ from CMB power spectra to date and in 4.1σ tension with the most precise distance-ladder-based measurement of H₀. The SPT-3G survey is planned to continue through at least 2023, with existing maps of combined 2019 and 2020 data already having ∼3.5× lower noise than the maps used in this analysis.

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