Light and strange baryons, two-baryon systems and the chiral symmetry of QCD

Abstract

Beyond the scale of spontaneous breaking of chiral symmetry light and strange baryons should be considered as systems of three constituent quarks with confining interaction and a chiral interaction that is mediated by Goldstone bosons between the constituent quarks. The flavor-spin structure and sign of the short-range part of the Goldstone boson exchange interaction reduces the $SU(6)_{FS}$ symmetry down to $SU(3)_F \times SU(2)_S$, induces hyperfine splittings and provides correct ordering of the lowest states with positive and negative parity. A unified description of light and strange baryon spectra calculated in a semirelativistic framework is presented. It is demonstrated that the same short-range part of the Goldstone boson exchange between the constituent quarks induces a strong short-range repulsion in $NN$ system when the latter is treated as $6Q$ system. Similar to the $NN$ system there should be a short-range repulsion in other $NY$ and $YY$ two-baryon systems. We also find that the compact 6Q system with the "H-particle" quantum numbers lies a few hundreds MeV above the $\Lambda\Lambda$ threshold. It then suggests that the deeply bound H-particle should not exist.