Implication of the Hubble tension for the primordial Universe in light of recent cosmological data

TL;DR

This paper investigates how resolving the Hubble tension with pre-recombination physics affects primordial cosmological parameters, suggesting a potential shift towards a scale-invariant spectrum if local H0 measurements are correct.

Contribution

It clarifies the relationship between Hubble tension resolution and primordial spectral index shifts using MCMC analysis with recent cosmological data.

Findings

Parameter shifts correlate with H0 variations.

A scale-invariant spectrum (n_s=1) may resolve the tension.

Results support a possible link between local H0 and primordial spectrum.

Abstract

In prerecombination resolutions of the Hubble tension, such as early dark energy, new physics before recombination shifts the values of relevant cosmological parameters so that the models can fit with cosmic microwave background and baryon acoustic oscillations observations as well as $\Lambda$CDM does. In this paper, we clarify how the parameter shifts are related with $\delta H_0$, particularly we find the shift of primordial scalar spectral index scales as ${\delta n_s}\simeq 0.4{\delta H_0\over H_0}$ by performing the Monte Carlo Markov chain analysis with the Planck2018+BAO+Pantheon+R19+Keck Array/BICEP dataset. A novel point of our result is that if the current $H_0$ measured locally is correct, complete resolution of the Hubble tension seems to be pointing to a scale invariant Harrison-Zeldovich spectrum, i.e. $n_s= 1$ for $H_0\sim 73$km/s/Mpc.