  In the non-relativistic limit, two types of dark matter axion interactions
with fermions are thought to dominate: one is induced by the spatial gradient
of the axion field and called the axion wind, and the other by the
time-derivative of the axion field, generating axioelectric effects. By
generalizing Schiff theorem, it is demonstrated that this latter operator is
actually strongly screened. For a neutral fermion, it can be entirely rotated
away and is unobservable. For charged fermions, the only effect that can peek
through the screening is an axion-induced electric dipole moment (EDM). These
EDMs are not related to the axion coupling to gluons, represent a prediction of
the Dirac theory analogous to the g = 2 magnetic moments, are not further
screened by the original Schiff theorem, and are ultimately responsible for
inducing the usual axioelectric ionization. The two main phenomenological
consequences are then that first the axion-induced neutron EDM could be several
orders of magnitude larger than expected from the axion gluonic coupling, and
second, that the electron EDM could also become available, and could actually
be highly sensitive to relic axions.
