Gravitational Breaking of the Grand Unified Theory Group and the Grand Unified Theory–Planck Hierarchy

It is shown that nonrenormalizable gravitational interactions in the Higgs sector of supersymmetric grand unified theories (GUTs) can produce the breaking of the unifying gauge group $G$ at the GUT scale $M_{\mathrm{GUT}}\sim {10}^{16}\mathrm{GeV}$. Such a breaking offers an attractive alternative to the traditional method where the superheavy GUT scale mass parameters are added ad hoc into the theory. The mechanism also offers a natural explanation for the closeness of the GUT breaking scale to the Planck scale. A study of two simple models endowed with this mechanism is presented.