The H0 tension: did a QCD meV axion emerge?

Abstract

I discuss the possibility that the difference in the measured Hubble constant Ho between the current, Late, and the z ~1100, Early, epochs is due to the emergence in between of a new particle. I connect that difference with a change in the effective cosmological constant observed by LambdaCDM, which is induced by the energy density of the vacuum of the field of the new particle. Then I try to provide the main characteristics of the particle, boson vs fermion and mass, using the measured change in Ho and a Lorentz invariant regularization of the energy density of vacuum, which relates it to such characteristics. The result indicates that a boson of mass in the range of few meV emerged. A QCD post-inflation cosmological axion in this mass range is allowed by recent analysis and its detection may be attempted according to recent experimental proposals.

misprints corrected, text refurbished, and many most recent references added; substance unchanged

References in corpus (5)

• The Hubble Hunter's Guide
• Implications of a transition in the dark energy equation of state for the $H_0$ and ${\sigma }_8$ tensions
• Laser induced fluorescence for axion dark matter detection: a feasibility study in YLiF${}_4$:Er${}^{3+}$
• The Cosmological Constant and Lorentz Invariance of the Vacuum State
• About the measure of the bare cosmological constant

Cited by in corpus (1)

• The Hubble tension: Change in dark energy or a case for modified gravity?