  We investigate a construction of five-dimensional (5D) grand unified theories
(GUTs) on an interval, which we call iGUTs. We analyze supersymmetric SO(10)
iGUT as an example, where the gauge multiplet is spread over the 5D bulk. The
SO(10) is directly reduced to the standard model gauge symmetry through the
interval boundary conditions. Notice that this rank reduction is impossible in
case of GUTs on orbifolds. Four scenarios are possible according to locations
(bulk or brane) of Higgs and matter fields. We investigate the gauge-coupling
unification, the proton decay, the SO(10) GUT features such as t-b-tau
unification and so on in each scenario. We also comment on the flavor
phenomenology.
