Splitting triplet and doublet in extra dimensions

A novel mechanism to realize the triplet-doublet splitting in supersymmetric SU(5) grand unified theories is proposed in the framework of higher-dimensional theories, where chiral multiplets are localized due to the kink configuration of a SU(5) singlet. An adjoint Higgs field that spontaneously breaks the SU(5) gauge symmetry is assumed to be involved in the localization process, splitting the wave functions of the color-triplet Higgs from its doublet counterpart. The resulting effective four-dimensional theory does not possess manifest SU(5) invariance. By adjusting couplings, the doublet mass can be exponentially suppressed. We also show that dimension-five proton decay from triplet Higgs exchange can be suppressed to a negligible level.