Chapter V Toward Realistic Treatment of Neutral Pion-Condensed State

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We describe several realistic treatments of the neutral pion (π^0)-condensed state or ALS structure. Treatments we call "realistic" here aim to incorporate the effects from (1) the isobar Δ(1232), (2) the reduction of the OPE-tensor force in the short range due to ρ meson, (3) the central force due to "σ" and ω meson, and (4) the short-range correlations between baryons. We present the following approaches to take account of these effects, i.e., an OBEP one with a schematic short-range correlation, a reaction-matrix one and two kinds of effective interaction approach. The transition density ρ_t(π^0) is found to be (2-3)ρ_0 in neutron matter and about 2.5ρ_0 in symmetric nuclear matter (ρ_0 being the nuclear density): The new phase is realized by the attractive effect of the OPE-tensor force enhanced by the Δ mixing which overwhelms the increase of the kinetic energy including the rest mass energy. The mechanism of the phase transition is clarified also in terms of the partial-wave contributions of the potential energy. It is found that the odd-state central potential plays an important role in assuring the stability of the π^0-condensed phase. It is shown that the effective nucleon mass is large in this phase in comparison with that in the Fermi gas phase.
理論物理学刊行会の論文
1993-06-20