Scale-invariant Helical Magnetic Fields from Inflation
  We discuss a model which can generate scale-invariant helical magnetic fields
on large scales ($\lesssim 1$Mpc) in the primordial universe. It is also shown
that the electric conductivity becomes significant and terminates
magnetogenesis even before reheating is completed. By solving the
electromagnetic dynamics taking conductivity into account, we find that
magnetic fields with amplitude $B\simeq 10^{-15}{\rm G}$ at present can be
generated without encountering a backreaction or strong coupling problem.
