Kaonic nuclear clusters- a new paradigm of particle and nuclear physics.

Λ^＊ = Λ(1405) plays an essential role in the formation of kaonic nuclear clusters (KNC). The simplest KNC, K^－pp, has the structure Λ^＊p = (K^－p)^I=0p, in which a real kaon migrates between two nucleons, mediating super-strong Λ^＊p attraction. Production data of K^－pp have been accumulated by DISTO, J-PARC E27 and J-PARC E15 experiments. For K^－K^－pp the attractive covalent bond of Λ^＊Λ^＊ is doubly enhanced compared to the Λ^＊p one. Consequently, Λ^＊ multiplet, (Λ^＊)_m, with m(m－1)/2 bonds becomes more stable than its corresponding neutron aggregate, (n)_m, at m = 8－12, suggesting the possible existence of stable Λ^＊ matter. A long-lived strangelet of (Λ^＊)_m=6 is presumed as a precursor. The production of K^－K^－pp by high-energy pp or heavy-ion collisions is awaited as a doorway to so-far unknown Λ^＊ matter.