Touch of Neutrinos on the Vacuum Metamorphosis: is the $H_0$ Solution Back?

TL;DR

This paper investigates whether the Vacuum Metamorphosis model, extended with neutrino physics and curvature, can simultaneously resolve the Hubble constant and matter clustering tensions in cosmology, finding some promising results but with increased model complexity.

Contribution

It demonstrates that the Vacuum Metamorphosis model, with neutrino extensions, can reconcile local H_0 measurements and matter clustering data, offering a potential solution to current cosmological tensions.

Findings

H_0 consistent with local measurements (~71 km/s/Mpc)

S_8 tension with weak lensing is resolved (~0.755)

Evidence for neutrino mass around 0.8 eV at >3σ

Abstract

With the entrance of cosmology in its new era of high precision experiments, low- and high-redshift observations set off tensions in the measurements of both the present-day expansion rate ($H_0$) and the clustering of matter ($S_8$). We provide a simultaneous explanation of these tensions using the Parker-Raval Vacuum Metamorphosis (VM) model with the neutrino sector extended beyond the three massless Standard Model flavours and the curvature of the universe considered as a model parameter. To estimate the effect on cosmological observables we implement various extensions of the VM model in the standard \texttt{CosmoMC} pipeline and establish which regions of parameter space are empirically viable to resolve the $H_0$ and $S_8$ tensions. We find that the likelihood analyses of the physically motivated VM model, which has the same number of free parameters as in the spatially-flat $\Lambda$CDM model, always gives $H_0$ in agreement with the local measurements (even when BAO or Pantheon data are included) at the price of much larger $\chi^2$ than $\Lambda$CDM. The inclusion of massive neutrinos and extra relativistic species quantified through two well known parameters $\sum m_{\nu}$ and $N_{\rm eff}$, does not modify this result, and in some cases improves the goodness of the fit. In particular, for the original VM+$\sum m_\nu$+$N_{\rm eff}$ and the Planck+BAO+Pantheon dataset combination, we find evidence for $\sum m_{\nu}=0.80^{+0.18}_{-0.22}~{\rm eV}$ at more than $3\sigma$, no indication for extra neutrino species, $H_0=71.0\pm1.2$~km/s/Mpc in agreement with local measurements, and $S_8=0.755\pm0.032$ that solves the tension with the weak lensing measurements. [Abridged]