  In this article, we take the scalar diquarks as point particles and describe
them as basic quantum fields, then introduce the SU(3) color gauge interaction
and new vacuum condensates to study the nonet scalar mesons as tetraquark
states with the QCD sum rules. Comparing with the conventional quark currents,
the diquark currents have the outstanding advantage to satisfy the two criteria
of the QCD sum rules more easily.
