From Peccei Quinn symmetry to mass hierarchy problem
We propose a non-universal $\mathrm{U}(1)_{X}$ gauge extension to the Standard Model (SM) and an additional Peccei-Quinn (PQ) global symmetry to study the mass hierarchy and strong CP problem. The scheme allows us to distinguish among fermion families and to generate the fermionic mass spectrum of particles of the SM. The symmetry breaking is performed by two scalar Higgs doublets and two scalar Higgs singlets, where one of these has the axion which turns out to be a candidate for Cold Dark Matter. The exotic sector is composed by one up-like $T$ and two down-like $J^{1,2}$ heavy quarks, two heavy charged leptons $E,\mathcal{E}$, one additional right-handed neutrino per family $ν_{R}^{e,μ,τ}$, and an invisible axion $a$. In addition, the large energy scale associated to the breaking of the PQ-symmetry gives masses to the right-handed neutrinos in such a way that the active neutrinos acquire eV-mass values due to the see-saw mechanism. On the other hand, from the non-linear effective Lagrangian, the flavour changing of the down quarks and charged leptons with the axion are considered.