Challenges for a QCD axion at the 10 MeV scale

Abstract

We report on an interesting realization of the QCD axion, with mass in the range $$ \mathcal{O} $$ O (10) MeV. It has previously been shown that although this scenario is stringently constrained from multiple sources, the model remains viable for a range of parameters that leads to an explanation of the Atomki experiment anomaly. In this article we study in more detail the additional constraints proceeding from recent low energy experiments and study the compatibility of the allowed parameter space with the one leading to consistency of the most recent measurements of the electron anomalous magnetic moment and the fine structure constant. We further provide an ultraviolet completion of this axion variant and show the conditions under which it may lead to the observed quark masses and CKM mixing angles, and remain consistent with experimental constraints on the extended scalar sector appearing in this Standard Model extension. In particular, the decay of the Standard Model-like Higgs boson into two light axions may be relevant and leads to a novel Higgs boson signature that may be searched for at the LHC in the near future.

The tiny (g-2) muon wobble from small-μ supersymmetry

“…2 A similar mechanism applies for (ge − 2) in the case of the QCD axion; see, for instance, ref. [54]. 3 There are also bounds from Coherent ν-Nucleus Scattering (CEνNS), although these are not yet competitive with the bounds from neutrino trident processes [58,59].…”

Shedding light on X17: community report

“…Alves and Weiner [59], Alves [60] and Liu et al [61] revisited the experimental constraints on the QCD axions in the O(10 MeV) mass window, and they found a variant axion model that remains compatible with the existing constraints. This reopened the possibility of solving the strong CP problem.…”

“…Finally, improved measurements of the electron anomalous magnetic dipole moment, (g − 2) e , could also significantly narrow down the available a (17) parameter space [59,139]. The current experimental situation regarding (g − 2) e is ambiguous, with the two most recent and precise determinations of the fine-structure constant, α, by Parker et al [140] and Morel et al [91], favoring different ranges for (g − 2) e that are discrepant by ∼ 3 σ .…”

The axion-baryon coupling in SU(3) heavy baryon chiral perturbation theory

“…Both, the fact that the Peccei-Quinn mechanism provides an elegant solution to the strong CP -problem, and that it at the same time might provide a solution to the missing matter problem of the universe, accounts for the unwavering interest in the axion, even though it has not been detected yet and its existence hence remains hypothetical. The original ("visible") Peccei-Quinn-Weinberg-Wilczek (PQWW) axion with a decay constant at the electroweak scale and a mass in the keV/MeV region seems to be ruled out experimentally [4,[23][24][25], although there are still attempts to make the experimental data compatible with the original model [26,27]. However, these models require a lot of additional assumptions including that these axions restrictively couple to the first generation fermions (up and down quark, electron) and are accidentally pion-phobic.…”