Slow-rolling scalar dynamics and as solution for the Hubble tension

Abstract

We construct a theoretical framework to interpret the Hubble tension by means of a slow-rolling dynamics of a self-interacting scalar field. In particular, we split the Friedmann equation in order to construct a system for the three unknowns, corresponding to the Hubble parameter $H$, the scalar field $ϕ$ and its self-interaction potential $V$, as functions of the redshift. In the resulting picture, the vacuum energy density is provided by a constant term in the potential $V(ϕ)$, while the corresponding small kinetic term is responsible for reproducing the apparent variation of the Hubble constant $H_0$ with the redshift. The emerging solution depends on two free parameters, one of which is fixed to account for the discrepancy between the values of $H_0$ as measured by the Super Nova Ia sample ($H_0=73.6\pm1.1$ km s$^{-1}$ Mpc$^{-1}$ (Brout et al., 2022)) and the Planck satellite data ($H_0=67.4\pm0.5$ km s$^{-1}$ Mpc$^{-1}$ (Aghanim et al., 2020)), respectively. The other parameter is instead determined by a fitting procedure of the apparent Hubble constant variation across the data corresponding to a 40 bin analysis of the Super Nova Pantheon sample, in each of which $H_0$ has been independently determined. The fundamental result of the present analysis is the emerging Hubble parameter as function of the redshift, which correctly takes the Super Nova Ia prediction at $z=0$ and naturally approaches the profile predicted by a flat $Λ$CDM model corresponding to the cosmological parameters detected by Planck. It is remarkable that this achievement is reached without reducing the Super Nova Ia data to a single point for determining $H(z=0)$, but accounting for the distribution over their redshift interval of observation, via the binned analysis.