Orbifold GUT inflation

We consider a scenario of cosmological inflation coming from a grand unified theory in higher-dimensional orbifold. Flatness of the potential is automatically guaranteed in this orbifold set-up thanks to the nonlocality of the Wilson line on higher dimensions and the local quantum gravitational corrections are exponentially suppressed. The spectral index of scalar perturbation () and a significant production of gravitational waves are predicted () in the perturbative regime of gauge interaction (1/g ₄ = (5-20) × 2πRM _Pl) where the size of compactification is constrained (-45) by the measurement of the scalar power spectrum ().