We study the possibility of producing a new kind of nuclear systems which in addition to ordinary nucleons contain a few antibaryons (B = p, Λ, etc.). The properties of such systems are described within the relativistic mean-field model by employing G-parity transformed interactions for antibaryons. Calculations are first done for infinite systems and then for finite nuclei from 4 He to 208 Pb. It is demonstrated that the presence of a real antibaryon leads to a strong rearrangement of a target nucleus resulting in a significant increase of its binding energy and local compression. Noticeable effects remain even after the antibaryon coupling constants are reduced by factor 3 − 4 compared to G-parity motivated values. We have performed detailed calculations of the antibaryon annihilation rates in the nuclear environment by applying a kinetic approach. It is shown that due to significant reduction of the reaction Q-values, the in-medium annihilation rates should be strongly suppressed leading to relatively long-lived antibaryonnucleus systems. Multi-nucleon annihilation channels are analyzed too. We have also estimated formation probabilities of bound B + A systems in pA reactions and have found that their observation will be feasible at the future GSI antiproton facility. Several observable signatures are proposed. The possibility of producing multi-quark-antiquark clusters is discussed.

The equation of state of hadron resonance gas at finite temperature and baryon density is calculated taking into account finite-size effects within the excluded volume model. Contributions of known hadrons with masses up to 2 GeV are included in the zero-width approximation. Special attention is paid to the role of strange hadrons in the system with zero total strangeness. A densitydependent mean field is added to guarantee that the nuclear matter has a saturation point and a liquid-gas phase transition. The deconfined phase is described by the bag model with lowest order perturbative corrections. The phase transition boundaries are found by using the Gibbs conditions with the strangeness neutrality constraint. The sensitivity of the phase diagram to the hadronic excluded volume and to the parametrization of the mean-field is investigated. The possibility of strangeness-antistrangeness separation in the mixed phase is analyzed. It is demonstrated that the peaks in the K/π and Λ/π excitation functions observed at low SPS energies can be explained by a nonmonotonous behavior of the strangeness fugacity along the chemical freeze-out line.