Monopole excitations of baryons in the NJL soliton model

The monopole excitations of the chiral soliton in the Nambu-Jona-Lasinio model are investigated. From the solutions to the Bethe-Salpeter equation in the background of the soliton It is argued that real large amplitude fluctuations do not exist in this channel. The corresponding collective coordinate, which parametrizes the extension of the soliton, is treated in the harmonic approximation. Canonical quantization of this coordinate yields a spectrum which reasonably well agrees with the empirical data for the Raper resonance, N(1440), and the corresponding one for the Delta, Delta(1600). Extensions oi the harmonic approximation are discussed.