Do JWST reionization (optical depth) puzzle, cosmological tensions, and CMB anomalies imply Harrison-Zel'dovich spectrum?

Abstract

The James Webb Space Telescope (JWST) has observed massive galaxies at high redshifts, which implies an earlier epoch of reionization (EoR) compared with the cosmic microwave background (CMB) results. In this paper, based on \texttt{Planck 2020} (NPIPE release), \texttt{ACT DR4} and \texttt{SPT-3G} data, if assumed a Harrison-Zel'dovich (HZ) primordial power spectrum in the standard cosmological model, we show that the redshift or optical depth of reionization is larger than the case of a power-law (PL) primordial power spectrum. In HZ-$ \Lambda $CDM model, the redshift of reionization is $ z_\text{reio} = 9.11 \pm 0.61 $, which is consistent with the JWST result that $ z_\text{reio} \approx 8.9 $. Moreover, the cosmological tensions, i.e. Hubble ($H_0$) tension and $ S_8 $ tension are alleviated in HZ-$ \Lambda $CDM case. The Hubble constant is $ H_0 = 70.38 \pm 0.35 \, \text{km}/\text{s}/\text{Mpc}$ and the structure growth parameter is $ S_8 = 0.7645\pm 0.0094 $ in HZ-$ \Lambda $CDM model. We also consider two extensions of $ \Lambda $CDM, including $ \Lambda $CDM$ + A_\text{L} $ and $ \Lambda $CDM$ + \Omega_\text{k} $ models. But the extensions of $ \Lambda $CDM with a HZ spectrum meet more serious CMB anomalies, i.e. lensing anomaly and spatial curvature anomaly as compared with the extensions of $ \Lambda $CDM with a PL spectrum. We discuss that these two CMB anomalies may come from the degeneracy of cosmological parameters.