Parity doublets in the baryon spectrum

Abstract

Physics of the low-lying and high-lying hadrons in the light flavors sector is reviewed. While the low-lying hadrons are strongly affected by both $U(1)_A$ and spontaneous $SU(2)_L \times SU(2)_R$ breakings, in the high-lying hadrons these symmetries are restored. A manifestation is a persistence of the chiral multiplet structure in both baryon and meson spectra. A fundamental origin of this phenomenon is that effects of quantum fluctuations of both quark and gluon fields must vanish at large $n$ or $J$ and a semiclassical description becomes adequate. A relation between the chiral symmetry restoration and the string picture of excited hadrons is discussed.