Orbitally excited hadrons

This review is devoted to the description of high-spin hadrons. A relativistic QCD-string model that reproduces the principal feature of the spectra of orbitally excited hadrons, namely, the linearity of Regge trajectories, is employed. Particular emphasis is placed on the inclusion of spin effects. For large orbital excitations, these effects appear as the spin-orbit interaction whose sign and magnitude are determined by confinement properties. Arguments are presented in support of the proposition that, for large orbital excitations, the spin-orbit interaction of quarks in the string model is largely due to the Thomas effect. The consequences of this hypothesis are analyzed phenomenologically, and the results are compared with experimental data. Specific predictions are obtained and await experimental verification. Orbital excitations of four-quark and dibaryon states are predicted.