SO(10) grand unification with a low-energy SU(2)R-symmetry-breaking scaleMR

Contrary to commonly held belief, we show that one can obtain a low value for ${\mathit{M}}_{\mathit{R}}$, the SU(2${)}_{\mathit{R}}$ breaking scale, in grand unification theories based on SO(10). This possibility emerges in the supersymmetric version of SO(10) with a judicious choice of Higgs content. The unification scale is found to be consistent with the constraint from proton decay. This result is first explicitly demonstrated using the one-loop renormalization group equations, and then a full two-loop analysis is carried out.