Christian T. Byrnes, Lukas Hollenstein, Rajeev Kumar Jain, Federico R. Urban
We propose a novel scenario to generate primordial magnetic fields during
inflation induced by an oscillating coupling of the electromagnetic field to
the inflaton. This resonant mechanism has two key advantages over previous
proposals. First of all, it generates a narrow band of magnetic fields at any
required wavelength, thereby allaying the usual problem of a strongly blue
spectrum and its associated backreaction. Secondly, it avoids the need for a
strong coupling as the coupling is oscillating rather than growing or decaying
exponentially. Despite these major advantages, we find that the backreaction is
still far too large during inflation if the generated magnetic fields are
required to have a strength of ${\cal O}(10^{-15}\, \Gauss)$ today on
observationally interesting scales. We provide a more general no-go argument,
proving that this problem will apply to any model in which the magnetic fields
are generated on subhorizon scales and freeze after horizon crossing.
View original:
http://arxiv.org/abs/1111.2030
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