QCD Sum Rules: Isospin Symmetry Breakings in Pion-Nucleon Couplings
  We use the method of QCD sum rules in the presence of an external pion field to investigate isospin symmetry breakings in pion-nucleon couplings. Possible manifestations of such isospin symmetry breaking are examined in the context of low-energy nucleon-nucleon ($NN$) scattering. We discuss numerical results in relation to both the existing data and other theoretical predictions. 
W-Y. P. Hwang, Ze-sen Yang, Y.S. Zhong, Z. N. Zhou, and Shi-lin Zhu