Axi-Higgs cosmology: Cosmic Microwave Background and cosmological tensions

TL;DR

The paper introduces the axi-Higgs model, involving an ultralight axion coupled to the Higgs field, which helps reduce the Hubble tension by modifying early universe cosmology and is testable with future atomic and spectral measurements.

Contribution

It presents a new axi-Higgs cosmological model and performs MCMC analyses showing its potential to alleviate the Hubble tension compared to standard models.

Findings

Hubble tension reduced to ~2.4σ with axi-Higgs model

H0 estimated at 71.34 ± 0.96 km/s/Mpc with combined data

Model predicts testable effects on atomic clocks and quasar spectra

Abstract

Non-canonical cosmology with an uplifted Higgs vacuum expectation value (Higgs-VEV) in the early universe is believed to provide the solution for existing tensions within the $\Lambda$CDM regime. We recently proposed a theoretical model called axi-Higgs to explore this framework. The axi-Higgs model features an ultralight axion with mass $m_a \sim 10^{-29}$ eV, which couples to the Higgs field such that the Higgs-VEV is driven by the axion background evolution. Phenomenologically, the axi-Higgs model is equivalent to $\Lambda$CDM+$m_e$+$\omega_a$ which is defined as $\Lambda$CDM with electron mass variation and the presence of an ultralight axion. In this paper, we perform Markov Chain Monte Carlo analyses to investigate the parameter space of axi-Higgs and compare it with $\Lambda$CDM, $\Lambda$CDM+$m_e$ where only electron mass variation is allowed, and $\Lambda$CDM+$\omega_a$ where only an ultralight axion is present. Combining observational data from Cosmic Microwave Background, Baryon Acoustic Oscillations, weak-lensing cosmic shear survey we found $H_0 = 69.4 \pm 1.3$ km/s/Mpc, which reduces the Hubble tension to approximately $2.4\sigma$. Including data from supernovae Type IA and local Hubble measurement from SH0ES we found $H_0 = 71.34 \pm 0.96$ km/s/Mpc. The presence of this Higgs-VEV-driving axion may be tested by atomic clock and quasar spectral measurements in the near future.