Low lying even parity excitations in the soliton bag model

The position of the Roper, 1440 MeV and the state at 1710 MeV the lowest excitations of the nucleon having the same quantum numbers as the nucleon itself, is investigated in the soliton bag model. As a small amplitude vibration of the soliton-quark fields (RPA), the frequency for the Roper comes out to be too low approx. 200 MeV compared to the experimental value of 500 MeV. Next, the one particle excitation state was coupled to the soliton O+ vibrational excitation and the matrix diagonalized. The splitting between the two P11 states including the one gluon exchange correction comes out to be approx. 264 MeV for one particular set of parameters. The Roper is mostly a particle excitation state and the 1710 state mostly vibrational. These configurations of the P11 states explain the transition modes qualitatively. (author)