Variety of SO(10) GUTs with Natural Doublet-Triplet Splitting via the Missing Partner Mechanism

TL;DR

This paper introduces a new class of SO(10) grand unified theories that unify symmetry breaking at a single scale and achieve natural doublet-triplet splitting through the missing partner mechanism, with realistic fermion masses and neutrino mixing.

Contribution

It proposes novel SO(10) models with a single symmetry-breaking scale and natural doublet-triplet splitting, expanding the landscape of GUT constructions.

Findings

Models achieve natural doublet-triplet splitting without fine tuning.

Realistic fermion masses and large neutrino mixing angles are possible.

Unique missing partner mechanism realization with 560+560̄ representations.

Abstract

We present a new class of unified SO(10) models where the GUT symmetry breaking down to the standard model gauge group involves just one scale, in contrast to the conventional SO(10) models which require two scales. Further, the models we discuss possess a natural doublet-triplet splitting via the missing partner mechanism without fine tuning. Such models involve $560+\ov{560}$ pair of heavy Higgs fields along with a set of light fields. The $560+\ov{560}$ are the simplest representations of SO(10) besides the $126+\ov{126}$ which contain an excess of color triplets over $SU(2)_L$ doublets. We discuss several possibilities for realizing the missing partner mechanism within these schemes. With the $126+\ov{126}$ multiplets, three viable models are found with additional fields belonging to ${210 + 2 \times 10 + 120}$, ${45 + 10 + 120}$, or ${210 + 16 + \ov{16} + 10 + 120}$. With the $560+\ov{560}$, a unique possibility arises for the missing partner mechanism, with additional ${2\times 10+ 320}$ fields. These models are developed in some detail. It is shown that fully realistic fermion masses can arise in some cases, while others can be made realistic by addition of vector--like representations. Naturally large neutrino mixing angles, including sizable $\theta_{13}$, can emerge in these models. The couplings of the $H_u(H_d)$ Higgs doublets of the MSSM which give masses to the up quarks (down quarks and leptons) are not necessarily equal at the grand unification scale and would lead to a new phenomenology at the low energy scales.