OPE coefficient functions in terms of composite operators only. Singlet   case
  A method for calculating coefficient functions of the operator product expansion, which was previously derived for the non-singlet case, is generalized for the singlet coefficient functions. The resulting formula defines coefficient functions entirely in terms of corresponding singlet composite operators without applying to elementary (quark and gluon) fields. Both "diagonal" and "non-diagonal" gluon coefficient functions in the product expansion of two electromagnetic currents are calculated in QCD. Their renormalization properties are studied. 
Alexander V. Kisselev
hep-ph hep-th