Abstract
The light mesons tend to cluster near certain values of mass. As was noticed some time ago, the emergent degeneracy is of the same type as the dynamical \(O(4)\) -symmetry of the Coulomb potential in the hydrogen atom. The meson mass spectrum can be well approximated by the linear Regge trajectories of the kind \(M^{2}=al+bn_{r}+c\) , where \(l\) and \(n_{r}\) are angular momentum and radial quantum numbers and \(a\) , \(b\) , \(c\) are parameters. Such a spectrum arises naturally within the hadron string models. Using 2024 data from the Particle Data Group, various fits for \(M^{2}(l,n_{r})\) were performed. Our analysis seems to confirm that \(a\approx b\) in the light non-strange mesons, i.e., their masses depend on the sum \(l+n_{r}\) as prescribed by the hydrogen-like \(O(4)\) -symmetry. Using the semiclassical approximation, we discuss which kind of hadron string models are more favored by the experimental data.
