Overview: deeply bound nuclear states of pions and kaons

An overview of the quest for deeply bound states of the two Nambu-Goldstone bosons (pions and kaons) is given. The deeply bound pionic states, the 1s states in heavy nuclei, serve as a unique probe for chiral symmetry restoration through the isovector s-wave π-nucleus interaction, as demonstrated in a recent systematic study in Sn isotopes. Narrow nuclear bound states of K have been predicted to exist with shrunk non-existent nuclear cores, and some experimental evidences have recently been obtained. They are expected to provide microscopic K-mediated dense nuclear systems, which are pertinent to kaon condensation without the aid of gravity. (author)