Abstract
We explore a common symmetrical origin for two long standing problems in particle physics: the strong CP and the fermion mass hierarchy problems. The Peccei-Quinn mechanism solves the former one with an anomalous global U(1)PQ symmetry. Here we investigate how this U(1)PQ could at the same time explain the fermion mass hierarchy. We work in the context of a four-Higgs-doublet model which explains all quark and charged fermion masses with natural, i.e. order 1, Yukawa couplings. Moreover, the axion of the model constitutes a viable dark matter candidate and neutrino masses are incorporated via the standard type-I seesaw mechanism. A simple extension of the model allows for Dirac neutrinos.
Highlights
The breaking of this symmetry at high scales of order (109 − 1015) GeV leads to a pseudo Goldstone boson, the axion a(x), and in consequence to the presence of the CPviolating term a GμνGμν
We explore a common symmetrical origin for two long standing problems in particle physics: the strong CP and the fermion mass hierarchy problems
We have presented a model where the strong CP, DM, neutrino masses, and fermion mass hierarchy problems find a common symmetrical origin in the Peccei-Quinn global and Abelian symmetry group, U(1)PQ
Summary
The central idea of the 4HDM model in [35] is to explain the mass hierarchy of the fermions by dividing them into four mass classes and assigning each of them to a single Higgs doublet:. Unless there is extreme tuning, the VEV of χ is required to be not too far away from the weak scale, which in turn implies that its Goldstone boson associated to the broken global symmetry cannot be the axion. Instead, another scalar A needs to be introduced, which will be associated to the axion. It couples to χ, and induces a VEV to it
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