SU(2)_L * SU(2)_R and U(1)_A restorations high in the hadron spectrum and what it tells us about

Abstract

Recent data for highly excited mesons suggest that not only the chiral $SU(2{)}_L\times SU(2{)}_R$ symmetry of QCD is restored high in the spectrum but also the $U(1{)}_A$ symmetry. This means that it is not a confining interaction in QCD which triggers the spontaneous breaking of chiral symmetry. The restoration of the $U(2{)}_L\times U(2{)}_R$ symmetry of the QCD Lagrangian implies the appearance of multiplets of this group high in the hadron spectra. Such type of multiplets is naturally explained within the string picture of confinement. It also supports the scenario that the $U(1{)}_A$ breaking is related to instantons and not to the gluonic interaction responsible for confinement.

Comments: 12 pages, LaTeX. The paper has been expanded and typos have been removed; to appear in Phys. Lett. B