Relaxing the limits on inflationary magnetogenesis
  Inflation has long been thought as the best way of producing primordial
large-scale magnetic fields. To achieve fields strong enough to seed the
galactic dynamo, most of the mechanisms operate outside conventional
electromagnetic theory. The latter is typically restored after the end of the
de Sitter phase. Breaking away from standard electromagnetism can lead to
substantially stronger magnetic fields by the end of inflation, thus
compensating for the their subsequent adiabatic depletion. We argue that the
drastic magnetic enhancement during the de Sitter era may no longer be
necessary because, contrary to the widespread perception, superhorizon-sized
magnetic fields decay at a slower pace after inflation. The principle behind
this claim is causality, which confines the post-inflationary electric currents
inside the horizon. Without the currents there can be no magnetic-flux freezing
on super-Hubble lengths. There, the magnetic decay-rate slows down, thus making
it much easier to produce primordial fields of astrophysical interest. To
quantify this qualitative statement, one can start from the current
galactic-dynamo requirements and `reverse engineer' the magnetic strengths
needed at the end of inflation, in order to produce astrophysically relevant
residual seeds today. Our results suggest that, depending on the magnetic
scale, mechanisms of inflationary magnetogenesis generating fields stronger
than $10^{17}$ G by the end of the de Sitter phase, could successfully seed the
galactic dynamo at present.
