Abstract
We analyse data on pi pi and gamma gamma scattering below 700 MeV within animproved analytic K-matrix model. This model is based on an effective theorywith couplings between resonances, hadrons and photons. The two-photon decay ofa resonance can proceed through intermediate transition into charged hadrons(here: pi^+ pi^-) and their subsequent annihilation or through a ``direct''transition into photons. Our analysis confirms the rather large total radiativewidth of the sigma/f_0(600) resonance which we find as (3.9 \pm 0.6) keV butsuggests its dominance by the pi pi rescattering process. This process is notsensitive to the internal structure of the resonance contrary to the directcomponent which we find small, (0.13 \pm 0.05) keV, and well consistent withthe expectations for an unmixed glueball according to the QCD sum rulecalculations.