What the study found
The study found that the cosmic microwave background (CMB, the afterglow radiation from the early universe) temperature power spectrum at large angular scales is lower than the best-fit Planck 2018 Lambda cold dark matter (Lambda CDM, the standard cosmological model) prediction. The authors report a low quadrupole, a dip between multipoles 20 and 27, and an overall low power level below multipole 30.
Why the authors say this matters
The authors conclude that these features do not plausibly arise from foreground contamination, systematic errors, masking, or mode mixing, given the nearly full-sky solution and different methodology used here. They also present a new low-multipole likelihood for use with the Cobaya package, and report that joint fits with higher-multipole Planck data are consistent with published Planck results.
What the researchers tested
The researchers measured the CMB temperature power spectrum at large angular scales using WMAP and Planck maps cleaned of foregrounds with a template-based approach described in the first paper of the series. They recovered nearly full-sky information for multipoles less than 30 with only 1% of pixels near the Galactic plane masked and without inpainting.
What worked and what didn't
The analysis recovered essentially the full-sky CMB information at multipoles below 30. It found a low quadrupole at 2.2 sigma compared with the best-fit Planck 2018 Lambda CDM spectrum, a dip over multipoles 20 to 27, and an overall low power level relative to the Lambda CDM prediction from higher multipoles. The overall multipole-below-30 amplitude constraint was consistent with published WMAP and Planck results at 1.2 sigma and 0.6 sigma, respectively, when statistical precision is taken into account.
What to keep in mind
The summary available here does not describe limitations beyond the stated masking and no-inpainting approach. The abstract reports consistency with published WMAP and Planck results and does not claim a discrepancy beyond the noted low-power features.
Key points
- The study reports low CMB temperature power at multipoles below 30.
- A low quadrupole is found at 2.2 sigma relative to the best-fit Planck 2018 Lambda CDM spectrum.
- A dip appears between multipoles 20 and 27.
- The authors say the features are unlikely to be caused by foregrounds, systematics, masking, or mode mixing.
- A new low-multipole likelihood is provided for the Cobaya package.
- A joint Lambda CDM fit with higher-multipole Planck data gives H0 = 67.35 ± 0.54 km s−1 Mpc−1.
Disclosure
- Research title:
- Low-multipole CMB temperature power is lower than Planck prediction
- Authors:
- Hayley C. Nofi, Graeme E. Addison, C. L. Bennett, Laura Herold, J. L. Weiland
- Institutions:
- Johns Hopkins University, Johns Hopkins University, Johns Hopkins University, Johns Hopkins University, Johns Hopkins University
- Publication date:
- 2026-07-01
- OpenAlex record:
- View
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