$H_0$ Ex Machina: Vacuum Metamorphosis and Beyond $H_0$

TL;DR

This paper investigates vacuum metamorphosis as a late-time transition model to explain the Hubble constant discrepancy, highlighting its successes and limitations when fitting various cosmological data.

Contribution

It introduces vacuum metamorphosis as a physically motivated late-time transition model with the same parameters as dm, analyzing its compatibility with diverse cosmic data.

Findings

Vacuum metamorphosis can yield high H_0 from CMB data.

The model fails to fit combined data from multiple distance probes.

Spatial curvature and growth data influence model viability.

Abstract

We do not solve tensions with concordance cosmology; we do obtain $H_0\approx 74\,$km/s/Mpc from CMB+BAO+SN data in our model, but that is not the point. Discrepancies in Hubble constant values obtained by various astrophysical probes should not be viewed in isolation. While one can resolve at least some of the differences through either an early time transition or late time transition in the expansion rate, these introduce other changes. We advocate a holistic approach, using a wide variety of cosmic data, rather than focusing on one number, $H_0$. Vacuum metamorphosis, a late time transition physically motivated by quantum gravitational effects and with the same number of parameters as \lcdm, can successfully give a high $H_0$ value from cosmic microwave background data but fails when combined with multiple distance probes. We also explore the influence of spatial curvature, and of a conjoined analysis of cosmic expansion and growth.