New aspects of MIT bag model

Summary

The original MIT bag model is reviewed. The rigidity of the surface of a nucleon is relaxed, through the realization of the orthogonality between states of quark mode and the suggestion of the possible instability of a rigid bag, so that the density of each quark is smoothly reduced to zero as one goes away from the center of mass of a nucleon. In this way the problem of nonconservation of axial current at the surface of a rigid bag is automatically resolved. Based on this relaxed surface of a nucleon which one may call a soft bag, some physical quantities such as the nucleon mass, its radius, and the density of each quark as a function of the distance from the center of mass are calculated. Also the range of nuclear interactions is successfully estimated. A possible thermodynamic feature is introduced, which suggests that three quarks in a nucleon are in the environment of the temperatureT≅≅9.4·10¹¹K.