Minimal Trinification

We study the trinified model, SU ( 3 ) C × SU ( 3 ) L × SU ( 3 ) R × Z 3 , with the minimal Higgs sector required for symmetry breaking. There are five Higgs doublets, and gauge-coupling unification results if all five are at the weak scale, without supersymmetry. The radiative see-saw mechanism yields sub-eV neutrino masses, without the need for intermediate scales, additional Higgs fields, or higher-dimensional operators. The proton lifetime is above the experimental limits, with the decay modes p → ¯ νK + and p → µ + K 0 potentially observable. We also consider supersymmetric versions of the model, with one or two Higgs doublets at the weak scale. The radiative see-saw mechanism fails with weak-scale supersymmetry due to the nonrenormaliza-tion of the superpotential, but operates in the split-SUSY scenario.