Mesons in nuclei and partial restoration of chiral symmetry

Recent topics on mesons in nuclei are discussed by especially emphasizing the role of the partial restoration of chiral symmetry in the nuclear medium. The spontaneously broken chiral symmetry in vacuum is considered to be incompletely restored in finite nuclear density systems with moderate reduction of the magnitude of the quark condensate. On the partial restoration of chiral symmetry, the wave function renormalization is important to be taken into account for the Nambu–Goldstone bosons. We also discuss the possible change of the meson properties in the nuclear medium and meson-nucleus systems for the K-bar, η, K⁺ and η′ mesons. (author)