Light Scalar Mesons as Tetraquarks within QCD Sum Rules

We examine the interpretation of the light scalar meson nonet as tetraquarkstates using QCD sum rules. With the interpolating current for the tetraquarkstates composed of scalar diquark and scalar antidiquark, first, we constructthe QCD sum rules by means of the operator product expansion up to theoperators of dimension 8 and show that there is no evidence of the coupling ofthe tetraquark states to the light scalar meson nonet. In order to have astable sum rule, we propose a "good" interpolating current for the tetraquarksbased on chirality arguments which includes scalar and pseudoscalardiquark--antidiquarks with equal weights. In particular, for the lowesttetraquark $\sigma$--meson, we perform detail analysis of the QCD sum rule andobtain mass for the $\sigma(600)$ around 780 MeV.Comment: 4 pages, 1 figure, Talk at the Yukawa International Seminar (YKIS) 2006, "New frontiers in QCD", Kyoto, Japa