Explaining fermions mass and mixing hierarchies through U(1)_X and Z₂ symmetries

Abstract For understanding the hierarchies of fermion masses and mixing, we extend the Standard Model (SM) gauge group with U (1) X and Z 2 symmetry. The field content of the SM is augmented by three heavy right-handed neutrinos, two new scalar singlets, and a scalar doublet. U (1) X charges of different fields are determined after satisfying anomaly cancellation conditions. In this scenario, the fermion masses are generated through higher-dimensional effective operators with O (1) Yukawa couplings. The small neutrino masses are obtained through type-1 seesaw mechanism using the heavy right-handed neutrino fields, whose masses are generated by the new scalar fields. We discuss the flavour-changing neutral current processes that arise due to the sequential nature of U (1) X symmetry. We have written effective higher-dimensional operators in terms of renormalizable dimension-four operators by introducing vector-like fermions.