A helpful analogy between the covalent bond and particle spectroscopy

It is proposed that meson resonances are linear combinations of q (q) over bar and meson-meson (MM); baryon resonances are combinations of qqq and meson-baryon (MB). Mixing between these combinations arises via decays of confined states to meson-meson or meson-baryon. There is a precise analogy with the covalent bond in molecular physics; it helps to visualize what is happening physically. One eigenstate is lowered by the mixing; the other moves up and normally increases in width. Cusps arise at thresholds. At sharp thresholds due to S-wave two-particle decays, these cusps play a conspicuous role in many sets of data. The overall pattern of light mesons is consistent with nearly linear Regge trajectories, hence q (q) over bar components. There is no obvious reason why this pattern should arise from dynamically generated states without q (q) over bar content.