No Arabic abstract
We present a new possibility for achieving doublet-triplet splitting naturally in supersymmetric SO(10) grand unified theories. It is based on a missing partner mechanism which is realized with the 126 + 126-bar Higgs superfields. These Higgs fields, which are also needed for generating Majorana right-handed neutrino masses, contain a pair of color triplets in excess of weak doublets. This feature enables us to remove the color triplets from the low energy spectrum without fine-tuning. We give all the needed ingredients for a successful implementation of the missing partner mechanism in SO(10) and present explicit models wherein the Higgs doublet mass is protected against possible non-renormalizable corrections to all orders. We also show how realistic fermion masses can be generated in this context.
The extended supersymmetric SO(10) model with missing partner mechanism is studied. An intermediate vacuum expectation value is incorporated which corresponds to the see-saw scale. Gauge coupling unification is not broken explicitly. Proton decay is found to satisfy the present experimental limits at the cost of fine-tuning some parameters.
We apply the perturbative grand unification due to renormalization to distinguish TeV-scale relics of supersymmetric $rm{SO}(10)$ scenarios. With rational theoretical constraints taken into account, we find that for the breaking pattern of either $rm{SU}(5)$ or Pati-Salam only extra matter $mathbf{16}$ supermultiplet of $SO(10)$ can appear at TeV scale, apart from MSSM spectrum.
In a class of gauged $U(1)$ extended Standard Models (SMs), the breaking of the $U(1)$ symmetry is not only a source for Majorana masses of right-handed (RH) neutrinos crucial for the seesaw mechanism, but also a source of stochastic gravitational wave (GW) background. Such $U(1)$ extended models are well-motivated from the viewpoint of grand unification. In this paper, we discuss a successful ultraviolet completion of a $U(1)$ extended SM by an $SO(10)$ grand unified model through an intermediate step of $SU(5) times U(1)$ unification. With a parameter set that is compatible with the $SO(10)$ grand unification, we find that a first-order phase transition associated with the $U(1)$ symmetry breaking can be strong enough to generate GWs with a detectable size of amplitude. We also find that the resultant GW amplitude reduces and its peak frequency becomes higher as the RH neutrino masses increase.
We extend the nonsupersymmetric SO(10) grand unification theories by adding a horizontal symmetry, which connects the three generations of fermions. Without committing to any specific symmetry group, we investigate the 1-loop renormalization group evolutions of the gauge couplings with one and two intermediate breaking scales. We find that depending on the SO(10) breaking chains, gauge coupling unification is compatible with only a handful of choices of representations of the Higgs bosons under the horizontal symmetry.
We study the proton lifetime in the $SO(10)$ Grand Unified Theory (GUT), which has the left-right (LR) symmetric gauge theory below the GUT scale. In particular, we focus on the minimal model without the bi-doublet Higgs field in the LR symmetric model, which predicts the LR-breaking scale at around $10^{10text{--}12}$ GeV. The Wilson coefficients of the proton decay operators turn out to be considerably larger than those in the minimal $SU(5)$ GUT model especially when the Standard Model Yukawa interactions are generated by integrating out extra vector-like multiplets. As a result, we find that the proton lifetime can be within the reach of the Hyper-Kamiokande experiment even when the GUT gauge boson mass is in the $10^{16text{--}17}$ GeV range. We also show that the mass of the extra vector-like multiplets can be generated by the Peccei-Quinn symmetry breaking in a consistent way with the axion dark matter scenario.