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Strong binding and shrinkage of single and double kbar~nuclear systems (K^-pp, K^-ppn, K^-K^-p and K^-K^-pp) predicted by Faddeev-Yakubovsky calculations

Non-relativistic Faddeev and Faddeev-Yakubovsky calculations were made for K^-pp, K^- ppn, K^-K^-p and K^- K^-pp kaonic nuclear clusters, where the quasi bound states were treated as bound states by employing real separable potential models for the K^ - - K^ - and the K^ - -nucleon interactions as well as for the nucleon-nucleon interaction. The binding energies and spatial shrinkages of these states, obtained for various values of the Kbar N interaction, were found to increase rapidly with the Kbar N interaction strength. Their behaviors are shown in a reference diagram, where possible changes by varying the KbarN interaction in the dense nuclear medium are given. Using the Lambda(1405) ansatz with a PDG mass of 1405 MeV/ c^2 for K^-p, the following ground-state binding energies together with the wave functions were obtained: 51.5 MeV ( K^ - pp ), 69 MeV ( K^ - ppn), 30.4 MeV ( K^ - K^ - p ) and 93 MeV ( K^ -K^ - pp ), which are in good agreement with previous results of variational calculation based on the Akaishi-Yamazaki coupled-channel potential. The K^ - K^ - pp state has a significantly increased density where the two nucleons are located very close to each other, in spite of the inner NN repulsion. Relativistic corrections on the calculated non-relativistic results indicate substantial lowering of the bound-state masses, especially of K^-K^-pp , toward the kaon condensation regime. The fact that the recently observed binding energy of K^-pp is much larger (by a factor of 2) than the originally predicted one may infer an enhancement of the KbarN interaction in dense nuclei by about 25 %, possibly due to chiral symmetry restoration. In this respect some qualitative accounts are given based on "clearing QCD vacuum" model of Brown, Kubodera and Rho.