Bag-like model for hadrons and its string-like properties

A specific bag-like model is proposed, in which quarks and gluons are confined in hadrons by an infinitely deep square-well potential of the spherical shape. In order to clarify various properties of our model in a framework of the field theory by using the soliton theory, the SU(2) Higgs-Kibble-like model is considered as a simple toy model of QCD. By the effect of the classical solution for an isospin singlet component of a complex isospinor scalar field, our confining potential is derived. It is shown that our model of hadrons has almost the same properties as the string model does, i.e., the infinite degeneracy of the internal states, the approximately linearly rising Regge trajectory (in the low energy region) and the Veneziano amplitude. These properties are derived from the contribution of the gluons only. (author)