Nucleon-nucleon forces from bags, quarks and boson exchange

Abstract

The concept of chiral symmetry in QCD is developed, especially the two possible realizations: i) the Wigner mode, in which fermions are massless, ii) the Goldstone mode, in which fermions acquire mass through spontaneous symmetry breaking. The former is used to describe quarks in the confinement region, the latter, to describe the external regions in which pions and σ-mesons carry, in a phenomenological way, the relevant degrees of freedom. A schematic treatment of interactions arising from quark-gluon exchange in region i), the perturbative region, is summarized and it is pointed out that in the primitive form given, perturbative QCD does not have much to say about the nucleon-nucleon force, at least it does not describe known empirical features, such as the spin-orbit interaction and the behavior of the central repulsion with energy. The chiral bag model, in which quarks are confined by fiat, is developed, starting from the M.I.T. bag model. Pions are coupled to the bag so as to conserve the axial-vector current. From this, boson exchange models can be built up. The non-perturbative solution of the model indicates a possibility of obtaining the non-relativistic constituent quark model from the chiral bag. It is pointed out that little bags must be very deformed, and consequences of this for physical quantities are worked out.