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. 
Ilja Dorsner, Pavel Fileviez Perez