A new SO(10) unified model is proposed based on a one-step breaking of SO(10) to the standard model gauge group $\mathrm{SU}(3{)}_C\times \mathrm{SU}(2{)}_L\times \mathrm{U}(1{)}_Y$ using a single 144 of Higgs. The symmetry breaking occurs when the SU(5) 24-plet component of 144 develops a vacuum expectation value. Further, it is possible to obtain from the same 144 a light Higgs doublet necessary for electroweak symmetry breaking using recent ideas of string vacua landscapes and fine-tuning. Thus the breaking of SO(10) down to $\mathrm{SU}(3{)}_C\times \mathrm{U}(1{)}_{em}$ can be accomplished with a single Higgs. We analyze this symmetry breaking pattern in the nonsupersymmetric as well as in the supersymmetric SO(10) model. In this scenario masses of the quarks and leptons arise via quartic couplings. We show that the resulting mass pattern is consistent with experimental data, including neutrino oscillations. The model represents an alternative to the currently popular grand unified scenarios.

• Received 30 June 2005

DOI:https://doi.org/10.1103/PhysRevD.72.095011