QUARK ANTIQUARK BOUND-STATES - RELATIVISTIC VERSUS NONRELATIVISTIC POINT-OF-VIEW

This brief review discusses various aspects of the description of hadrons as bound states of quarks in the simpler example of mesons, which are regarded as being composite of a (constituent) quark and an antiquark. It is shown how a recently derived relativistic virial theorem may be used to cast some light on the interplay between the (semi)relativistic and (maybe only effectively) nonrelativistic treatment of bound states. Furthermore, a new relativistic approach to fermion-antifermion bound states is sketched and applied to predict analytically a few selected general features of the meson spectrum.