  Nonresonant inelastic x-ray scattering (NIXS) is a possible tool to detect
charge excitations in electron systems. In addition, multipole transitions at
high-momentum-transfer region open a new possibility to determine
orbital-selective electronic excitations in multi-orbital itinerant 3d electron
systems. As a theoretical example, we chose the antiferromagnetic state of iron
arsenides and demonstrate that the orbital-selective excitations are detectable
by choosing appropriate momentum transfer in NIXS. We propose that both NIXS
and resonant inelastic x-ray scattering are complementary to each other for
fully understanding the nature of orbital excitations in multi-orbital
itinerant electron systems.
