The Hubble Constant in the Axi-Higgs Universe

Abstract

The $\hat{I}›$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 $\hat{I}›$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.

15 pages, 11 figures, final version published on PRR Letter