The nature of the light scalar mesons from their radiative decays

Abstract

The nature of the light scalar mesons is one of the most intriguing open challenges in hadronic spectroscopy. It is argued that radiative decays involving these scalars can serve as an important decisive tool in establishing their nature. In particular, special emphasis is made on the radiative decays of the scalars themselves (in addition to the radiative decays of the phi-meson with the scalars appearing in the final state), including their two-photon decays. All the above mentioned processes are considered in detail in the (point-like) kaon molecule model of the scalars and explicit predictions for the decay widths are made. In addition, finite-range corrections to the point-like results are investigated, with a special attention payed to gauge invariance of the decay amplitude. Finally, the conclusion is made that experimental data on the radiative decays with the light scalar mesons involved strongly support the molecule assignment for the latter.