The Hubble Constant in the Axi-Higgs Universe

TL;DR

The paper explores the axi-Higgs model, which couples an ultralight axion to the Higgs field, demonstrating its potential to simultaneously relax the Hubble constant and S8 tensions in cosmology, and provides specific parameter constraints.

Contribution

It introduces the axi-Higgs model as a variation of $\\Lambda$CDM that addresses multiple cosmological tensions and offers testable predictions with current data.

Findings

The axi-Higgs model reduces the H0 tension to about 1.5 km/s/Mpc.

It also alleviates the S8 tension, bringing it closer to weak-lensing measurements.

The model's benchmark scenario yields H0 = 69.9 ± 1.5 km/s/Mpc and S8 = 0.8045 ± 0.0096.

Abstract

The $\Lambda$CDM model provides an excellent fit to the CMB data. However, a statistically significant tension emerges when its determination of the Hubble constant $H_0$ is compared to the local distance-redshift measurements. The axi-Higgs model, which couples an ultralight axion to the Higgs field, offers a specific variation of the $\Lambda$CDM model. It relaxes the $H_0$ tension as well as explains the $^7$Li puzzle in Big-Bang nucleosynthesis, the clustering $S_8$ tension with the weak-lensing data, and the observed isotropic cosmic birefringence in CMB. In this paper, we demonstrate how the $H_0$ and $S_8$ tensions can be relaxed simultaneously, by correlating the axion impacts on the early and late universe. In a benchmark scenario ($m=2 \times 10^{-30}$ eV) selected for experimental tests soon, the analysis combining the CMB+BAO+WL+SN data yields $H_0 = 69.9 \pm 1.5$ km/s/Mpc and $S_8 = 0.8045 \pm 0.0096$. Combining this (excluding the SN (supernovae) part) with the local distance-redshift measurements yields $H_0 = 72.42 \pm 0.76$ km/s/Mpc, while $S_8$ is slightly more suppressed.