Vector-like quarks at the origin of light quark masses and mixing

Abstract

We show how a novel fine-tuning problem present in the Standard Model can be solved through the introduction of a $$Z_6$$ flavour symmetry, together with three $$Q = - 1/3$$ quarks, three $$Q = 2/3$$ quarks, as well as a complex singlet scalar. The $$Z_6$$ symmetry is extended to the additional fields and it is an exact symmetry of the Lagrangian, only softly broken in the scalar potential, in order to avoid the domain-wall problem. Specific examples are given and a phenomenological analysis of the main features of the model is presented. It is shown that even for vector-like quarks with masses accessible at the LHC, one can have realistic quark masses and mixing, while respecting the strict constraints on processes arising from flavour changing neutral currents. The vector-like quark decay channels are also described