SU(5) orbifold GUT in noncommutative geometry

In this paper, we apply the orbifold GUT mechanism to the SU(5) model in noncommutative geometry, including the fermionic sector. Imposing proper parity assignments for “constituent fields” of bosons and fermions, the couplings between fermions and the heavy bosons , , and are prohibited by the parity symmetry. As a result, the derived fermionic Lagrangian is just that of the standard model, and proton decay is forbidden at tree level. If quantum fluctuation respects the parity symmetry, the process will be naturally suppressed or even forbidden completely