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arXiv · 2210.09018

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

William Giarè·Fabrizio Renzi·Olga Mena·Eleonora Di Valentino·Alessandro Melchiorri
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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.

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William Giarè, Fabrizio Renzi, Olga Mena, Eleonora Di Valentino, Alessandro Melchiorri. 2022-10-17. Is the Harrison-Zel'dovich spectrum coming back? ACT preference for $n_s \sim 1$ and its discordance with Planck. https://doi.org/10.1093/mnras%2Fstad724

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