The role of the pion pair term in the theory of the weak axial meson   exchange currents
  The structure of the weak axial pion exchange current is discussed in various models. It is shown how the interplay of the chiral invariance and the double counting problem restricts uniquely the form of the pion potential term, in the case when the nuclear dynamics is described by the Schroedinger equation with the static nucleon-nucleon potential. 
B. Mosconi, P. Ricci, E. Truhlik