We report on a novel ab initio approach for nuclear few- and many-body systems with strangeness. Recently, we developed a relevant no-core shell model technique which we successfully applied in first calculations of lightest $Lambda$ hypernuclei. The
use of a translationally invariant finite harmonic oscillator basis allows us to employ large model spaces, compared to traditional shell model calculations, and use realistic nucleon-nucleon and nucleon-hyperon interactions (such as those derived from EFT). We discuss formal aspects of the methodology, show first demonstrative results for ${}_{Lambda}^3$H, ${}_{Lambda}^4$H and ${}^4_Lambda$He, and give outlook.
In-medium ${bar K}N$ scattering amplitudes developed within a new chirally motivated coupled-channel model due to Cieply and Smejkal that fits the recent SIDDHARTA kaonic hydrogen 1s level shift and width are used to construct $K^-$ nuclear potential
s for calculations of $K^-$ nuclear quasi-bound states. The strong energy and density dependence of scattering amplitudes at and near threshold leads to $K^-$ potential depths $-Re V_K approx 80 -120$ MeV. Self-consistent calculations of all $K^-$ nuclear quasi-bound states, including excited states, are reported. Model dependence, polarization effects, the role of p-wave interactions, and two-nucleon $K^-NNrightarrow YN$ absorption modes are discussed. The $K^-$ absorption widths $Gamma_K$ are comparable or even larger than the corresponding binding energies $B_K$ for all $K^-$ nuclear quasi-bound states, exceeding considerably the level spacing. This discourages search for $K^-$ nuclear quasi-bound states in any but lightest nuclear systems.
Relativistic mean field calculations of multi-$bar{K}$ hypernuclei are performed by adding $K^-$ mesons to particle-stable configurations of nucleons, $Lambda$ and $Xi$ hyperons. For a given hypernuclear core, the calculated $bar{K}$ separation energ
y $B_{bar{K}}$ saturates with the number of $bar{K}$ mesons for more than roughly 10 mesons, with $B_{bar{K}}$ bounded from above by 200 MeV. The associated baryonic densities saturate at values 2-3 times nuclear-matter density within a small region where the $bar{K}$-meson densities peak, similarly to what was found for multi-$bar{K}$ nuclei. The calculations demonstrate that particle-stable multistrange ${N,Lambda,Xi }$ configurations are stable against strong-interaction
We report on self-consistent calculations of single-K^- nuclear states and multi-Kbar nuclear states in 12C, 16O, 40Ca and 208Pb within the relativistic mean-field (RMF) approach. Gradient terms motivated by the p-wave resonance Sigma(1385) are found
to play a secondary role for single-K^- nuclear systems where the mean-field concept is acceptable. Significant contributions from the Kbar N -> pi Lambda conversion mode, and from the nonmesonic Kbar NN -> YN conversion modes which are assumed to follow a rho^2 density dependence, are evaluated for the deep binding-energy range of over 100 MeV where the decay channel Kbar N -> pi Sigma is closed. Altogether we obtain K^- total decay widths of 50-100 MeV for binding energies exceeding 100 MeV in single-K^- nuclei. Multi-Kbar nuclear calculations indicate that the binding energy per Kbar meson saturates upon increasing the number of Kbar mesons embedded in the nuclear medium. The nuclear and Kbar densities increase only moderately and are close to saturation, with no indication of any kaon-condensation precursor.
