HYDROGEN-LIKE CLASSIFICATION FOR LIGHT NONSTRANGE MESONS

The recent experimental results on the spectrum of highly excited light nonstrange mesons are known to reveal a high degree of degeneracy among different groups of states. We revise some suggestions about the nature of the phenomenon and put the relevant ideas into the final shape. The full group of approximate mass degeneracies is argued to be SU(2)(f) x I x O(4), where I is the degeneracy of isosinglets and isotriplets and O(4) is the degeneracy group of the relativistic hydrogen atom. We discuss the dynamical origin and consequences of considered symmetry with a special emphasis on distinctions of this symmetry from the so-called chiral symmetry restoration scenario.