The Hubble Tension in Light of the Symmetry of Scale Invariance

TL;DR

This paper explores how the scale-invariant vacuum (SIV) cosmological model can reconcile the Hubble tension by linking early and late Universe properties without conflict, challenging the standard $ ext{Lambda}$CDM assumptions.

Contribution

It introduces the SIV model as an alternative to $ ext{Lambda}$CDM, demonstrating its ability to resolve the Hubble tension through cosmological tests and physical connections at recombination.

Findings

SIV model constrains $\

Omega_m

H_0

Abstract

When the expansion rate of the Universe at recombination is used to infer the present expansion rate $H_0$, the value derived in the $\Lambda$CDM model, $H_0=67.4$ km/s/mpc, is about in 6$\, \sigma$ tension with the value measured locally, $H_0=74$ km/s/mpc. In this work, we consider instead the expansion history in the context of the symmetry of scale-invariant vacuum (SIV model). We first perform two major cosmological tests: the Hubble diagram for type-Ia supernovae and the fundamental relation between $H_0$, the age of the Universe, and the total density of matter, $\Omega_m$. This allows us to constrain $\Omega_m$ in SIV, with both tests giving the best agreement for $\Omega_m \simeq 0.20$. We then study the physical connections of the dynamical and thermal states of the Universe at recombination with the present Hubble constant, $H_0$, and the present temperature, $T$, in the $\Lambda$CDM and SIV contexts. We find that, in SIV, the properties at recombination may be conveyed to the present ones ($T=2.726$ and $H_0$ at $z=0$) without any tension, indicating $H_0=74$ km/s/mpc in spite of the anchoring on the CMB. This is due to the slightly different expansion and temperature histories of the two cosmological models. Importantly, this happens to occur for $\Omega_m \simeq 0.20$, as constrained in SIV with supernovae and cosmic age. This suggests that the Hubble tension currently found between $H_0$ values in the early and late Universe may simply be the result of $\Lambda CDM$ ignoring the small but still measurable effects of scale invariance.