  We show the necessity of two-nucleon axial currents and associated pion
emission/ absorption operators for the partial conservation of the axial
current (PCAC) nuclear matrix elements with arbitrary nuclear dynamics
described by a nonrelativistic Schroedinger equation. As examples we construct
such nonrelativistic axial two-body currents in the linear- and heterotic (g_A
= 1.26) sigma models, with an optional isoscalar vector (omega) meson exchange.
The nuclear matrix elements obey PCAC only if the nuclear wave functions used
in the calculation are solutions to the Schroedinger equation with the static
one-meson-exchange potential constructed in the respective (sigma) model. The
same holds true for the nucler pion production amplitude, since it is
proportional to the divergence of the axial current matrix element, by virtue
of PCAC. Thus we found a new consistency condition between the pion
creation/absorption operator and the nuclear Hamiltonian. We present examples
drawn from our models and discuss implications for one-pion-two-nucleon
processes.
