Relativistic model of mesons with current quark masses

A relativistic quark model of mesons is proposed. In this model, the current quarks and antiquarks satisfy the Dirac equations, and the contribution of the gluon field at large distances is described by a straight-line Nambu-Goto quantum string. The current quark masses and the string tension appear to be basic parameters of the model. The gluon-field contribution at small distances, which does not grow with the meson spin, is taken into account phenomenologically. The model describes fairly well the mass spectrum of mesons--from the pion to the Υ meson--that lie on the leading Regge trajectories (in terms of the potential model, these mesons represent the lowest radial excitations) and makes it possible to derive the current quark masses. The relativistic wave functions of composite mesons have been obtained and used to show that the spin structure of the light-quark mesons differs substantially from the predictions of the nonrelativistic quark model. Mass values have been predicted for new mesons, and a comparison has been made with the results obtained on the basis of the Godfrey-Isgur potential model