Two-Photon Decays of Mesons in a Relativistic Quark Model
  We present a relativistic calculation of two-photon decays for heavy and light mesons in the framework of the Salpeter equation for quark-antiquark states. The meson-photon-photon vertex is computed by reconstructing the Bethe-Salpeter vertex function and evaluating the four-dimensional Feynman diagram with off-shell quark amplitudes. The two-photon width for light and heavy quarkonia up to spin equal six are calculated with different parameter sets taken from the literature thus giving a complete overview on the mesonic two-photon physics. We find that relativistic effects including the negative energy components of the wave function are important for any two-photon width - even for heavy quarkonia - yielding a remarkable agreement with available data. 
C.R. Munz (University of Bonn, Germany)