  Both the relativistic and non-relativistic model explain very well low-energy
nuclear phenomena, but in a physically different way from each other. There
seems to be no low-energy phenomenon to answer which model is more reasonable.
In order to explore a difference between two models, high momentum transfer
phenomena are investigated. First it is shown that the neutron spin-orbit
charge density in the relativistic model reproduces very well experimental data
on elastic electron scattering which have not been explained in the
non-relativistic model. Next it is predicted that the relativistic Coulomb sum
value is strongly quenched, compared with the non-relativistic one. This
quenching is owing to the anti-nucleon degrees of freedom, which make the
nucleon size larger and equivalently the vector-meson mass smaller in nuclear
medium. New experiment on the Coulomb sum values around the momentum transfer
1GeV is expected to distinguish the relativistic from the non-relativistic
model.
