Unification versus proton decay in SU(5)

We investigate unification constraints in the simplest renormalizable non-supersymmetric SU(5) framework. We show that in the scenario where the Higgs sector is composed of the 5-, 24-, and 45-dimensional representations the proton could be practically stable. We accordingly demonstrate that of all the SU(5) scenarios only the non-renormalizable one with the 5-, 24-, and 15-dimensional Higgs multiplets can be verify if low-energy supersymmetry is not realized in nature.