Pion condensation in neutron star matter

An estimation of the threshold density of π0 condensation in neutron star matter is given, by adopting the effective neutron-neutron interaction which is constructed from a phenomenological nuclear potential. The effective interaction in the triplet state is favorable to π0 condensation, even though it puts up the threshold density into the higher density region, as compared with the case where no effective interaction is considered. The effective interaction in the singlet state is, however, unfavorable to condensation, unless we use the slightly larger effective mass than the usually used one as well as the pion-nucleon coupling constant increased due to the modification peculiar to the many-nucleon system. (auth.)