Progress of Theoretical Physics Supplement No. 112, 1993 Chapter III Characteristic Aspects of Pion-Condensed Phases

Characteristic aspects of pion-condensed phases are described in a simple model, for the system involving only nucleons and pions which interact through the TC- N P-wave interac-tion. We consider one typical version in each of three kinds of pion condensation; the one of neutral pions (TC0), the one of charged pions (TCc) and the combined one in which both the TC 0 and TCc condensations are coexistent. Emphasis is put on the description to clarify the novel structures of the nucleon system which are realized in the pion-condensed phases. At first, it is shown that the TC0 condensation is equivalent to the particular nucleonic phase realized by a structure change of the nucleon system, where the attractive first-order effect of the one-pion-exchange (OPE) tensor force is brought about coherently. The aspects of this phase are characterized by the layered structure with a specific spin-isospin order with one-dimensional localization (named the ALS structure in short), which provides the source function for the condensed TC0 field. We utilize both descriptions with use of fields and potentials for the TC0 condensation. Next, the TCc condensation realized in neutron-rich matter is described by adopting a version of the traveling condensed wave. In this phase, the nucleonic structure becomes the Fermi gas consisting of quasi-neutrons described by