  There is increasing interest in the role played by pseudo Nambu-Goldstone
bosons (pNGBs) in the construction of string-inspired models of inflation. In
these models the inflaton is expected to be coupled to gauge fields, and will
lead to the generation of magnetic fields that can be of cosmological interest.
We study the production of such fields mainly focusing on the model of
N-flation, where the collective effect of several pNGBs drives inflation.
Because the produced fields are maximally helical, inverse cascade processes in
the primordial plasma increase significantly their coherence length. We discuss
under what conditions inflation driven by pNGBs can account for the observed
cosmological magnetic fields. A constraint on the parameters of this class of
inflationary scenarios is also derived by requiring that the magnetic field
does not backreact on the inflating background.
