A two-generational ${\rm SU}(7)$ model with extended weak sector: mass hierarchies, mixings, and the flavor non-universality

TL;DR

This paper explores an ${ m SU}(7)$ grand unified theory with extended weak sector, proposing a symmetry breaking pattern that explains fermion mass hierarchies, mixings, and flavor non-universality through a generalized seesaw mechanism.

Contribution

It introduces a novel ${ m SU}(7)$ model with specific symmetry breaking steps and mechanisms to generate fermion mass hierarchies and flavor non-universality, including the role of multiple Higgs fields.

Findings

Fermion mass hierarchies are explained via a generalized seesaw mechanism.

The model predicts vectorlike fermions and flavor-changing weak currents.

Flavor non-universality arises from the extended weak sector.

Abstract

We study a possible gauge symmetry breaking pattern in an ${\rm SU}(7)$ grand unified theory, which describes the mass origins of all electrically charged SM fermions of the second and the third generations. Two intermediate gauge symmetries of ${\cal G}_{341}\equiv {\rm SU}(3)_c \otimes {\rm SU}(4)_W \otimes {\rm U}(1)_{X_0}$ and ${\cal G}_{331}\equiv {\rm SU}(3)_c \otimes {\rm SU}(3)_W \otimes {\rm U}(1)_{X_1}$ arise above the electroweak scale. SM fermion mass hierarchies between two generations can be obtained through a generalized seesaw mechanism. The mechanism can be achieved with suppressed symmetry breaking VEVs from multiple Higgs fields that are necessary to avoid tadpole terms in the Higgs potential. Some general features of the ${\rm SU}(7)$ fermion spectrum will be described, which include the existence of vectorlike fermions, the tree-level flavor changing weak currents between the SM fermions and heavy partner fermions, and the flavor non-universality between different SM generations from the extended weak sector.