Soliton models for nuclear physics

Abstract

Nontopological soliton models have been successfully used to incorporate the quark structure of hadrons into nuclear physics. These are phenomenological field theories which can be motivated from QCD, but are simple enough to permit calculations of nucleon structure and interactions. Three types of model are covered here: soliton bag models, chiral quark-meson models, and colour dielectric models. All involve quarks interacting with various phenomenological boson fields. The forms of their mean-field solutions (solitons) are presented. Arguments relating the models to QCD are outlined. For quark-meson models these go via intermediate NJL-type models. These suggest that that the nonlocalities of the effective action may be well described by the valence quarks alone; the effect of the Dirac sea is to generate kinetic and potential energies for the mesons. Unlike the Skyrme model, the quark-meson models have explicit quark degrees-of-freedom. Their quantisation is thus not restricted to 1/Nc expansions, and they can retain the nonlocal nature of the effective action. A colour-dielectric field can be obtained by a block-spinning approach to QCD. This can give absolute confinement provided the dielectric field vanishes in the vacuum. Dynamical calculations in these models are described, many of which are based on the use of coherent states to provide quantum states corresponding to these solitons. These calculations include recoil corrections, derivation of an effective wave equation for a composite nucleon, and calculations of NN scattering. In models with strong pion fields states of good spin and isospin are constructed from hedgehog solitons. Excited states can be treated with an extension of the random-phase approximation. This is applied to breathing-mode excitations, as well as to strange baryons. A possible way to treat nuclear matter in these models is outlined. © 1990.