Estimate of Quantum corrections to the Mass of the Chiral Soliton in the Nambu--Jona--Lasinio Model

The Bethe--Salpeter equation for pion fluctuations off the chiral soliton in the Nambu--Jona--Lasinio model is constructed. By Goldstone's theorem this equation has rotational and translational zero modes because the classical soliton is a localized stationary field configuration which violates rotational and translational invariance. Furthermore, the proper normalization of the fluctuating eigen--modes is obtained. Second quantization of the pion fluctuations off the chiral soliton provides an energy functional of the pion fluctuations which formally coincides with that of a harmonic oscillator. The corresponding quantum corrections to the soliton mass together with the semi--classical cranking prescription yield reasonable predictions for the masses of the nucleon and the $\Delta$--resonance when the constituent quark mass is chosen to be about 400MeV. These calculations are, to some extend, hampered by the non--confining character of the Nambu--Jona--Lasinio model. Comments on the $1/N_C$ counting scheme are added.