Structure of baryonic system with pion condensation and its implication in neutron star problems

This paper deals with recent works made from the viewpoint of the ALS model by developing these studies: (1) In order to take into account the OPE effect enhanced by Δ-mixing leading to pion condensation and short-range effect on equal footing, a reaction matrix theory in the ALS structure by Tamiya and myself is presented. The calculated results in neutron matter enable us to understand the mechanism of the structure change by using the same notions in the usual nuclear matter theory. (2) Study on the ALS structure in neutron matter based on the sigma-model made by Tatsumi is reported, by putting emphasis on his recent result that πsup(c) condensation is realized in a limited range of density upon π0 condensation, namely under the ALS structure. (3) The effects of the ALS structure and its associated aspects of pion condensation of neutron star problems are briefly discussed. (orig./HSI)