On inflating magnetic fields, and the backreactions thereof
  We investigate in more depth the issue of backreaction in models that attempt
at generating cosmological magnetic fields at inflation. By choosing different,
physically motivated, parametrisations, we are able to isolate the core of the
problem, namely the existence, alongside the wanted magnetic field, of its
electric counterpart, which turns out quite generally to be stronger and
redder. We were also able to identify a few more interwoven weak spots (the
typically very high scale of inflation, the width of the spectrum of modes
processed by inflation, the blindness of the amplification mechanism to the
energy scale processed), in a way independent on the specifications of the
coupling between inflation and electromagnetism. Despite having stripped down
the problem to the core, the obstacles encountered appear insurmountable,
thereby posing a challenge to inflation as the incubator of cosmological
magnetism.
