A possibility of describing a sequential gauge symmetry as a part of the dihedral flavor symmetry and its implications

TL;DR

The paper investigates embedding a hierarchical sequential $U(1)_X$ gauge structure within an $A_4$ flavor-symmetric framework, treating sequential terms as higher-order corrections to a leading non-sequential flavor structure. It demonstrates that mass matrices in both the quark and lepton sectors arise from a combination of sequential (dimension-five/6) and non-sequential terms, with mediation between sectors required to realize realistic mixing patterns. The breaking of family universality under $A_4$ is identified as a key source of mixing, while the flavor-specific Higgs vevs and sector-specific scalars govern the size and pattern of the mixing, particularly enhancing lepton-sector mixing. The work also outlines extensions to other flavor symmetries and future directions for numerical analysis and seesaw-realization within this mixed sequential/non-sequential framework.

Abstract

We present a method in which the dimension-five and -six terms in a sequential gauge symmetry can coexist with that of the dihedral flavor symmetry. We start with the contents in the model proposed in a sequential gauge symmetry, meeting the conditions for the contents to be described in the flavor symmetry, build up the mass matrices and discuss its implications. Given that the breaking of the symmetry only takes place in the dimension-five and -six terms in the mass matrix of the charged fermion sectors, via the flavor-specific Higgs scalars, we address how adding the non-sequential contents as a part of the model can be realized and why adding such is needed. In doing so, we illustrate that the terms in the sequential gauge could be understood as the higher-order terms, the correction terms, and that in the non-sequential flavor symmetry as that of the leading order. We present that the mediation between the sequential and the non-sequential term within each sector is needed to take the hierarchical scheme of the charged and the neutral lepton sectors into account. Our result could be understood as an illustration of introducing the sequential gauge as a cause for the mixing and that of the coexistence of the sequential and the non-sequential gauge terms, and can be applied to other flavor model. Seeing the non-sequential term leading us to the mass matrix and the sequential term cross-contaminating between sectors could be an indication of the size of the mass being independent from that of the mixing in the leading order and a reason for the size of the mixing in the lepton sector being larger than that of the quark sector.