Grand unified theory with a stable proton

We demonstrate that a phenomenologically viable four-dimensional grand unified theory with no proton decay can be constructed. This is done in the framework of the minimal nonsupersymmetric SU(5) GUT by introducing new representations and separating the physical quark and lepton fields into different multiplets. In such a theory all beyond Standard Model particles are naturally heavy, but one can tune the parameters of the model such that gauge coupling unification is achieved and some of the new particles are at the TeV scale and accessible at the LHC.