Gauge coupling unification in a 6D SO(10) orbifold GUT

We consider the gauge coupling running in a six-dimensional SO(10) orbifold GUT model. The bulk gauge symmetry is broken down to the standard model gauge group with an extra U(1)X by orbifold boundary conditions and the extra U(1)X is further broken through the U(1)B-L breaking with bulk hyper multiplets. We obtain the corrections of Kaluza-Klein massive modes to the running of the gauge couplings and discuss their implication to the successful gauge coupling unification.