The role of qqqq(q)over-bar components in the nucleon and the N(1440) resonance

The role of q (q) over bar components in the nucleon and the N(1440) resonance is studied by explicit coupling of the lowest positive parity qqqq (q) over bar state to the qqq components in the harmonic oscillator quark model. The lowest energy qqqq (q) over bar component, where the 4-quark subsystem has the flavor-spin symmetry [4](FS)[22](F)[22](S), is close in energy to the lowest positive parity excitation of the nucleon in the qqq quark model. The confining interaction leads to a strong mixing of the qqqq (q) over bar system and the positive parity excited state of the qqq system. This result is in line with the phenomenological indications for a two-component structure of the N(1440) resonance. The presence of substantial q (q) over bar components in the N(1440) can bring about a reconciliation of the constituent quark model with the large empirical decay width of the N (1440). 0 2006 Elsevier B.V. All rights reserved.