Mechanism of Hadron Mass Splitting in the Quark Model

The analogy between the hadron mass splitting (e.g., between N and Δ) and the atomic hyperfine structure is often taken for granted, but is in fact surprising in view of the large difference in the strength of the interactions involved. We attempt an improved treatment of the quark-quark interaction by including some nonperturbative effects of gluon exchange processes. We find that the gluon effect on the mass splitting tends to be much weaker than that based on the analogue of the Fermi-Breit potential. This would require a value of the quark-gluon coupling constant αs much larger than that usually accepted. This uncomfortable situations can be avoided by assuming a specific type of color dependence of the confining potential.