  The existence of large-scale magnetic fields in galaxies is well established,
but there is no accepted mechanism for generating a primordial field which
could grow into what is observed today. We discuss a model which attempts to
account for the necessary primordial field by invoking a pseudo-Goldstone boson
coupled to electromagnetism. The evolution of this boson during inflation
generates a magnetic field; however, it seems difficult on rather general
grounds to obtain fields of sufficient strength on astrophysically interesting
scales.
