The Primordial power spectrum from the largest to smallest CMB scales

arXiv:2608.24413 · astro-ph.CO, hep-ph, hep-th · Submitted 2026-08-25 · Read on arXiv

astro-ph.CO, hep-ph, hep-th

Submitted: 2026-08-25

Updated: 2026-08-25

Comments: 45 pages, 25 figures and 5 tables

License: http://creativecommons.org/licenses/by/4.0/

The gist: We reconstruct the primordial power spectrum (PPS) across the full range of cosmological scales accessible to Cosmic Microwave Background (CMB) observations.

Terminology

Regularization — 53× in this paper · explained in 3 episodes
ACT Data — 23× in this paper · explained in 1 episode
Consistency — 7× in this paper · explained in 3 episodes
Modified Richardson-Lucy — 6× in this paper
Anisotropy — 5× in this paper · explained in 3 episodes
Cosmic Microwave Background — 4× in this paper
Atacama Cosmology Telescope — 3× in this paper
Adam — 2× in this paper · explained in 2 episodes
Bispectrum — 2× in this paper · explained in 3 episodes
Degeneracy — 2× in this paper · explained in 3 episodes
Korea Astronomy and Space Science Institute — 2× in this paper
Anusandhan National Research Foundation — 1× in this paper
Boltzmann Equation — 1× in this paper · explained in 2 episodes
Fisher Information — 1× in this paper · explained in 3 episodes
Hubble Tension — 1× in this paper · explained in 9 episodes
Robustness — 1× in this paper · explained in 5 episodes
Weak Lensing — 1× in this paper · explained in 2 episodes

Abstract

We reconstruct the primordial power spectrum (PPS) across the full range of cosmological scales accessible to Cosmic Microwave Background (CMB) observations. Using the Modified Richardson--Lucy algorithm, we perform free-form reconstructions through deconvolution of Planck PR3 and PR4, Atacama Cosmology Telescope (ACT) DR6, and South Pole Telescope 3G (SPT-3G) D1 data. Across different regularization schemes, we find no evidence for significant deviations from a power-law primordial spectrum. The reconstructed spectra show a strong correlation between Planck and ACT, even at the level of localized features over their overlapping range, 0.07 < k < 0.14, Mpc-1, demonstrating consistency between the two observations. Using a complementary parametric Bayesian reconstruction, we find that the previously discussed preference for a blueward tilt in the ACT data at small scales is preferred only at the 1σ level.

Terminology

Abstract

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