Strange tribaryons as K-mediated dense nuclear systems

K nuclei, which means that a K- meson is deeply bound in nuclei, are considered to have lots of interesting properties. Recently, two K nuclei, ppnK- and pnnK- which are called 'strange tribaryons', have been experimentally confirmed by Iwasaki group. Their experimental results brought us two puzzles; i) ppnK- is more deeply bound than our prediction, and ii) how is pnnK- that is more deeply bound than ppnK-? We point out that i) relativistic effect and enhancement of KN interaction and ii) nucleon configuration of pnnK- are important to solve these puzzles. The observed pnnK- is considered to have an excited configuration, (Os)2(Op), not the ground one, (Os)3. Due to such excited configuration, it can gain attraction from I = 0 KN interaction and NN LS interaction. (author)