theta_C from the Dihedral Flavor Symmetries D_7 and D_14

TL;DR

This paper constructs a Standard Model extension with dihedral flavor symmetries D_7 x Z_2 to explain the Cabibbo angle and lepton mixing, demonstrating that group theory can predict mixing angles and vacuum configurations.

Contribution

It develops a low-energy model incorporating dihedral flavor symmetries to predict quark and lepton mixing angles, including the Cabibbo angle, based solely on group theoretical properties.

Findings

Successfully reproduces quark mixing parameters with D_7 symmetry.

Shows nearly tri-bimaximal lepton mixing can emerge from dihedral groups.

Numerically demonstrates vacuum alignment consistent with the model.

Abstract

In [1] it has been shown that the Cabibbo angle theta_C might arise from a dihedral flavor symmetry which is broken to different (directions of) subgroups in the up and the down quark sector. This leads to a prediction of theta_C in terms of group theoretical quantities only, i.e. the index n of the dihedral group D_n, the index j of the fermion representation 2_j and the preserved subgroups indicated by m_u and m_d. Here we construct a low energy model which incorporates this idea. The gauge group is the one of the Standard Model and D_7 x Z_2 ^(aux) serves as flavor symmetry. The additional Z_2 ^(aux) is necessary in order to maintain two sets of Higgs fields, one which couples only to up quarks and another one coupling only to down quarks. We assume that D_7 is broken spontaneously at the electroweak scale by vacuum expectation values of SU(2)_L doublet Higgs fields. The quark masses and mixing parameters can be accommodated well. Furthermore, the potential of the Higgs fields is studied numerically in order to show that the required configuration of the vacuum expectation values can be achieved. We also comment on more minimalist models which explain the Cabibbo angle in terms of group theoretical quantities, while theta_{13}^q and theta_{23}^q vanish at leading order. Finally, we perform a detailed numerical study of the lepton mixing matrix V_{MNS} in which one of its elements is entirely determined by the group theory of a dihedral symmetry. Thereby, we show that nearly tri-bi-maximal mixing can also be produced by a dihedral flavor group with preserved subgroups.