Nonlinear corrections in basic problems of electro- and magneto-statics in the vacuum

We point that any theoretically found value for an electromagnetic multipole of a baryon or a meson should be subjected to ``renormalization'' due to nonlinearity of QED. We find third-power nonlinear corrections to the Coulomb and other static electric fields, as well as to the electric and magnetic dipole fields, as we work within QED with no background field. The nonlinear response function on which we base our consideration is the fourth-rank polarization tensor, calculated within the local (infrared) approximation of the effective action, the results being applicable to weakly varying and not too strong fields. It is established that the nonlinear corrections to magnetic moments of some baryons and mesons, fitting the present approximate scheme, match the existing indeterminacy in their theoretical values.