  We propose a new mechanism for magnetic field generation from inflation, by
which strong magnetic fields can be generated on cosmological scales. These
fields may be observable by cosmic microwave background radition measurements,
and may have a dynamical impact on structure formation. The mechanism is based
on the observation that a light nearly minimally coupled charged scalar may be
responsible for the creation of a negative photon mass-squared (provided the
scalar field coupling to the curvature scalar is small but negative), which in
turn results in abundant photon production - and thus in growing magnetic
fields - during inflation.
