Is the Harrison-Zel'dovich spectrum coming back? ACT preference for $n_s\sim 1$ and its discordance with Planck

Abstract

The Data Release 4 of the Atacama Cosmology Telescope (ACT) shows an agreement with an Harrison-Zel'dovich primordial spectrum ($n_s=1.009\pm 0.015$), introducing a tension with a significance of $99.3\%$ CL with the results from the Planck satellite. The discrepancy on the value of the scalar spectral index is neither alleviated with the addition of large scale structure information nor with the low multipole polarization data. We discuss possible avenues to alleviate the tension relying on either neglecting polarization measurements from ACT or in extending different sectors of the theory.

8 pages, 5 figures, 2 tables. Accepted for publication in MNRAS

References in corpus (19)

• A Comprehensive Measurement of the Local Value of the Hubble Constant with 1 km/s/Mpc Uncertainty from the Hubble Space Telescope and the SH0ES Team
• Planck evidence for a closed Universe and a possible crisis for cosmology
• CMB polarization features from inflation versus reionization
• On the most constraining cosmological neutrino mass bounds
• Intermediate inflation in light of the three-year WMAP observations
• Towards early dark energy and $n_s$=1 with Planck, ACT and SPT
• Health checkup test of the standard cosmological model in view of recent Cosmic Microwave Background Anisotropies experiments
• Towards hybrid inflation with $n_s=1$ in light of Hubble tension and primordial gravitational waves
• Cosmological constraints on slow-roll inflation: an update
• Return of Harrison-Zeldovich spectrum in light of recent cosmological tensions
• Cosmological implications of $n_s\approx 1$ in light of the Hubble tension
• Quantifying the global "CMB tension" between the Atacama Cosmology Telescope and the Planck satellite in extended models of cosmology
• Curvaton field and intermediate inflationary universe model
• Reionization constraints from five-year WMAP data
• On the consistency of $\Lambda$CDM with CMB measurements in light of the latest Planck, ACT, and SPT data
• Impact of reionization on CMB polarization tests of slow-roll inflation
• Harrison-Z'eldovich primordial spectrum is consistent with observations
• Evidence for horizon-scale power from CMB polarization
• D-term inflation in braneworld models: Consistency with cosmic-string bounds and early-time Hubble tension resolving models

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• Dynamical Dark Energy Beyond Planck? Constraints from multiple CMB probes, DESI BAO and Type-Ia Supernovae
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• Inflation, the Hubble Tension and Early Dark Energy: an alternative overview
• Sign Switching in Dark Sector Coupling Interactions as a Candidate for Resolving Cosmological Tensions
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• On the consistency of $\Lambda$CDM with CMB measurements in light of the latest Planck, ACT, and SPT data
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