Semileptonic D decay into scalar mesons: a QCD sum rule approach
  Semileptonic decays of D-mesons into scalar hadronic states are investigated. Two extreme cases are considered: a) the meson decays directly into an uncorrelated scalar state of two two mesons and b) the decay proceeds via resonance formation. QCD sum rules including instanton contributions are used to calculate total and differential decay rates under the two assumptions. 
H.G. Dosch, E.M. Ferreira, F.S. Navarra and M. Nielsen