This Letter demonstrates that the nonrelativistic approximation breaks down for the lighter hadrons with the conventional $\mathrm{qq}$ one-gluon exchnage potential. This is mainly due to the Coulomb and the short-range hyperfine interactions. To overcome this difficulty, some phenomenological interactions with a long-range spin dependence are proposed. The validity of treating the spin-dependent term as a perturbation is examined.

• Received 14 January 1980

DOI:https://doi.org/10.1103/PhysRevLett.44.1369