Analysis the $f_0(980)$ and $a_0(980)$ mesons as four-quark states with   the QCD sum rules
  In this article, we take the point of view that the scalar mesons $ f_0(980)$ and $a_0(980)$ are diquark-antidiquark states $(qq)_{\bar{3}}(\bar{q}\bar{q})_3$, and devote to determine their masses in the framework of the QCD sum rules approach with the interpolating currents constructed from scalar-scalar type and pseudoscalar-pseudoscalar type diquark pairs respectively. The numerical results indicate that the scalar mesons $ f_0(980)$ and $a_0(980)$ may have two possible diquark-antidiquark substructures. 
Zhi-Gang Wang (NCEPU), Wei-Min Yang (USTC)