We investigate colorless (mesonic) $3q\text{−}q\overline{q}$ components in the nucleon and the Roper resonance $N^{*}(1440)$. Starting from constituent quarks and gluons we estimate the excitation of $q\overline{q}$ pairs in a gluon exchange model with the strong coupling constant extracted from a comparison with a nonperturbative resonating group calculation of the $\pi ,\eta ,\rho$, and ω content of the nucleon. Applying the same model to the Roper resonance, we find as the most striking result a very strong scalar-isoscalar σ-content of the $N^{*}(1440)$ with a strength of the $3q\text{−}q\overline{q}$ configurations comparable to the $3q$ component itself.

• Received 10 October 2006
• Publisher error corrected 3 July 2007

DOI:https://doi.org/10.1103/PhysRevC.75.067001