EFFECTIVE KAON MASS IN NUCLEAR-MATTER FROM CHIRAL LAGRANGIANS

The s-wave kaon-nucleon and kaon-nuclear interactions are investigated in heavy-baryon chiral perturbation theory. The relevant low energy constants in an effective chiral Lagrangian up to next-to-next-to-leading order are constrained by the on-shell threshold kaon-nucleon scattering data. The s-wave interaction of off-shell kaons with nucleons is predicted to be consistent with the dispersion theoretic fit. The s-wave self-energy of kaons in nuclear matter is computed following Weinberg's power counting scheme in the independent particle approximation. The effective mass of K- in nuclear matter decreases with the density, thus possibly leading to condensation phenomena at high densities, while that of K+ increases with the density. Chiral corrections to the effective mass of K- is, however, repulsive and increases both with the matter density and with the strangeness content in the nucleon, although two-body contributions are relatively small up to seven times the normal nuclear matter density rho(0). The critical density for kaon condensation in neutron stars, for example, is expected to be about (3 similar to 6)rho(0) for (20 similar to 0)% strangeness content in the nucleon. The discrepancy between the approach of effective chiral Lagrangians and the phenomenological approach based on PCAC (partial conservation of axial current) and current algebra tends to be less severe as we include higher-order chiral corrections. The approach of effective chiral Lagrangians seems more reliable in taking the medium effects into account.