Minimal axion model from flavor

We show that solving the flavor problem of the Standard Model with a simple $U(1{)}_H$ flavor symmetry naturally leads to an axion that solves the strong $CP$ problem and constitutes a viable Dark Matter candidate. In this framework, the ratio of the axion mass and its coupling to photons is related to the SM fermion masses and predicted within a small range, as a direct result of the observed hierarchies in quark and charged lepton masses. The same hierarchies determine the axion couplings to fermions, making the framework very predictive and experimentally testable by future axion and precision flavor experiments.

Figure 1

The axiflavon band (light brown) projected on the axion parameter space: mass vs photon coupling defined in Eq. (15). The standard KSVZ/DFSZ band is shown in light yellow. The grey exclusion region is obtained from the combination of various axion constraints that are summarized in the legend. The dashed colored lines show the projected reach of future axion experiments. The solid blue line is the exclusion reach from current flavor experiments for an axiflavon model with ${\kappa }_{sd}/N=1$ [cf. Eq. (20)]. The dashed blue line depicts the expected reach of future flavor experiments for the same choice of parameters.