Charge symmetry breaking in pion-nucleon coupling constant : QCD sum   rule approach
  Using the vacuum-to-pion matrix element of the correlation function of the interpolating fields of the two nucleons, the isospin splitting in the diagonal pion-nucleon coupling constant has been studied in the framework of the conventional QCD sum rule. Some of the implications of this splitting has also been discussed. 
J.P. Singh and Alka Upadhyay