The quasiparticle interaction, a shield of nuclear matter against pion condensation

A microscopic calculation is presented for the quasiparticle interaction in nuclear matter. As a starting point a Brueckener G-matrix is used, which is derived from realistic potentials (Reid soft core, HM2Δ). Keeping the full complexity of this interaction, the excitation modes for the different spin-isospin channels are evaluated. The effects of isobar excitation [Δ(3, 3)] are also taken into account. The exchange of the corresponding phonons is added to the bare G-matrix and the influence of this so-called crossed channel renormalization on the interaction of quasiparticles at the Fermi surface is discussed. This renormalization of the particle-hole interaction increases drastically the critical density for pion condensation in nuclear matter.