Dynamical $\mathbf{O(4)}$-Symmetry in the Light Meson Spectrum within the Framework of the Regge Approach

Abstract: The light mesons tend to cluster near certain values of mass. As was noticed almost twenty years 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 on a simple qualitative level which kind of string-like semirelativistic approaches are more favored by the experimental data.