Axion mass prediction from minimal grand unification

We propose a minimal realization of the Peccei-Quinn mechanism in a realistic SU(5) model, where the axion mass is directly connected to the grand unification scale. Accounting for constraints from proton decay, collider searches and gauge coupling unification, we predict the axion mass $m_a\in [4.8,6.6]\mathrm{neV}$. The upper bound relaxes to $m_a<330\mathrm{neV}$ for a tuned flavor structure of the proton decay operators. The predicted mass window will be complementarily probed by the axion dark matter experiments ABRACADABRA and CASPER-Electric, which could provide indirect evidence for the scale of grand unification before the observation of proton decay.

Figure 1

Maximal triplet mass parameter as a function of the axion mass. Grey, blue and red bands denote, respectively, the correlation at 1, 2 and 3 loops (shaded regions encode the $1\sigma$ uncertainty on the electroweak gauge couplings). The full horizontal (vertical) red line is the current exclusion from LHC (SK), the dashed horizontal (vertical) red line is the projected exclusion from HL-LHC (HK).

Figure 2

Axion coupling to photons, $g_{a\gamma }$, versus axion mass $m_a$. The blue regions give the projected sensitivities of broadband (“Broad”) and resonant (“Res.”) search modes of ABRACADABRA from Ref. [28].

Figure 3

Axion coupling to the nucleon EDM operator, $g_{aD}$, versus axion mass $m_a$. The blue regions give the projected sensitivities of CASPEr-Electric from Ref. [30]. The short, full blue line reflects a factor of 3 improvement in sensitivity for a search just concentrated on the preferred mass region.

Figure 4

Axion coupling to the nucleons, $g_{aN}$, versus axion mass $m_a$. The blue regions give the projected sensitivities of CASPEr-Wind from Ref. [30].