DFSZ Axion Couplings Revisited

Understand

Among many possibilities, solar axion has been proposed to explain the electronic recoil events excess observed by Xenon1T collaboration, although it has tension with astrophysical observations.

• The axion couplings, to photon $g_{a\gamma}$ and to electron $g_{ae}$ play important roles.
• These couplings are related to the Peccei-Quinn (PQ) charges $X_f$ for fermions.
• In most of the calculations, $g_{a\gamma}$ is obtained by normalizing to the ratio of electromagnetic anomaly factor $E = TrX_f Q^2_f N_c$ ($N_c$ is 3 and 1 for quarks and charged leptons respectively) and QCD anomaly factor $N = TrX_q T(q)$ ($T(q)$ is quarks' $SU(3)_c$ index).