Nonrenormalizable Grand Unification Utilizing the Leptoquark Mechanism of Neutrino Mass

We analyze a nonsupersymmetric grand unified theory whose particle content is that of the Georgi–Glashow model augmented only by scalars from the 10 and 35 representations. A prediction of our model is a color sextet, weak isodoublet whose mass lies at 1 TeV (10 TeV) and that does not couple to Standard Model fermions at tree level. The leptoquark mechanism through which Majorana neutrinos radiatively acquire their masses relates the neutrino mass matrix to that of the down-type quarks. A consequence of this relation and perturbativity of coupling constants is the upper bound of $2.5 \times 10^{15}$ GeV on the masses of the scalar leptoquarks $S_1^{*}$ and ${\widetilde{R}}_{2}$. Electroweak mixing of these leptoquarks induces a B-L violating decay of the proton which indirectly contrains the mass of ${\widetilde{R}}_{2}$ to be greater than $1.7 \times 10^9$ GeV. We find the grand unification scale to exceed $1.4 \times 10^{16}$ GeV in all scenarios considered.