Nonperturbative treatment of gluons and pseudoscalar mesons in baryon spectroscopy

We study baryon spectroscopy including the effects of pseudoscalar meson exchange and one gluon exchange potentials between quarks, using nonperturbative, hyperspherical method calculations. We find that a model that includes only gluon exchange cannot simultaneously describe the Roper and $P$-wave excitation energies. Using only pseudoscalar meson exchange partially cures this problem, but at the cost of using a relatively large pion quark coupling constant. However, one gets a similar agreement with data in a model with both effects by using a quark-meson coupling constant compatible with the measured pion-nucleon coupling constant, and a value of ${\alpha }_s\approx 0.35$.