2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/204601We study the pion-nucleon P_33 and P_11 scattering, where the Delta and the Roper resonances are seen, respectively. We use the Lippmann-Schwinger equation extended to couple to a one-body state, and investigate nature of these resonances by taking and omitting a one-baryon state into account. We see validity and puzzle of the standard quark model interpretation, for the Delta and the Roper resonances, respectively.4 pages, 3 figures, to appear in the proceedings of the 11th International Conference on Meson-Nucleon Physics and the Structure of the Nucleon, Sept. 10th-14th 2007 (MENU 2007), Juelich, GermanyNuclear Theorytext