Two or Four: A Hint from Scalar Mesons in Radiative phi Decays ?

In this write-up, we summarize our recent analysis of radiative decays involving light scalar mesons. Our analysis using the vector meson dominance model at tree level indicates that it may be difficult to distinguish $qqbar{q}bar{q}$ picture and $qbar{q}$ picture for the light scalar nonet. Our result on the process of $phi to pi^0 eta gamma$ shows that the derivative-type $f_0 Kbar{K}$ interaction reproduces experimental data below 950 GeV well, but gives a poor fit above 950 GeV, i.e., in the energy region around the mass of $a_0(980)$, but that the discrepancy can be compensated by the effect of the $K$ loop.