Mesonic Content of the Nucleon and the Roper Resonance

Abstract

We investigate colorless (mesonic) 3q-q qbar components in the nucleon and the Roper resonance N*(1440). Starting from constituent quarks and gluons we estimate the excitation of quark-antiquark pairs in a gluon exchange model with the strong coupling constant extracted from a comparison with a non-perturbative resonating group calculation of the pi, eta, rho and omega content of the nucleon. Applying the same model to the Roper resonance, we find as the most striking result a very strong scalar-isoscalar sigma content of the N*(1440) with a strength of the 3q-q qbar configurations comparable to the 3q component itself.