  We analyze the generation of primordial magnetic fields during de Sitter
inflation in a Lorentz-violating theory of Electrodynamics containing a
Chern-Simons term which couples the photon to an external four-vector. We find
that, for appropriate magnitude of the four-vector, the generated field is
maximally helical and, through an inverse cascade caused by turbulence of
primeval plasma, reaches at the time of protogalactic collapse an intensity and
correlation length such as to directly explain galactic magnetism.
