Possible Explanation of the Electron Positron Anomaly at 17 MeV in $^8Be$ Transitions Through a Light Pseudoscalar

TL;DR

This paper investigates whether a light pseudoscalar particle with a mass of about 17 MeV can explain the electron-positron anomaly observed in $^8$Be transitions, by estimating its Yukawa couplings and analyzing experimental constraints.

Contribution

The study provides a detailed estimation of the pseudoscalar's Yukawa couplings and demonstrates how they can account for the $^8$Be anomaly while satisfying experimental constraints.

Findings

Yukawa couplings to quarks are about 0.3 times the Higgs coupling.

Couplings to electrons must be larger than four times the Higgs coupling.

Loop contributions to flavor-changing processes need to cancel at least at 10%.

Abstract

We estimate the values of Yukawa couplings of a light pseudoscalar A with a mass of about 17 MeV, which would explain the $^8Be$ anomaly observed in the Atomki pair spectrometer experiment. The resulting couplings of A to up and down type quarks are about 0.3 times the coupling of the standard Higgs boson. Then constraints from K and B decays require that loop contributions to flavour changing vertices cancel at least at the 10% level. Constraints from beam dump experiments require the coupling of A to electrons to be larger than about 4 times the coupling of the standard Higgs boson, leading to a short enough A life time consistent with an explanation of the anomaly.