Abstract
We study the possibility that some of the low-lying nucleon and isobar resonances in the P11 and P33 channels, respectively, are surface excitations of the N and bag-model ground states. In particular we concentrate here on the gluon- and pion-exchange forces between quarks as they emerge from a chiral bag model. The mass splittings in the calculated N- spectrum compare surprisingly well to the experimentally well-established mass differences. The best fit is obtained with a fine-structure constant /sub s/ = 1.6 and a volume energy density B/sup 1/4/ = 130 MeV. (No attempt has been made to reproduce the nucleon ground state.) We predict an isobar state at around 1600 MeV, which is interpreted as the version of the N(1440) Roper resonance described in a chiral bag model with a nonstatic surface.
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