Isospin splitting in the pion-nucleon couplings from QCD sum rules

We use QCD sum rules for the three point function of a pseudoscalar and two nucleonic currents in order to estimate the charge dependence of the pion nucleon coupling constant gNNπ coming from isospin violation in the strong interaction. The effect can be attributed primarily to the difference of the quark condensates and . Assuming that the π0 is a pure isostate we obtain for the splitting (|gppπ0|-|gnnπ0|)/gNNπ an interval of 0.8*10-2 to 2.3*10-2, the uncertainties coming mainly from the input parameters. In order to obtain the coupling to a physical π0 we have to take π-η mixing into account leading to an interval of 1.2*10-2 to 3.7*10-2. The charged pion nucleon coupling is found to be the average of |gppπ0| and |gnnπ0|. Electromagnetic effects are not included