Palatini approach and large-scale magnetogenesis
  Large-scale magnetogenesis is analyzed within the Palatini approach when the
gravitational action is supplemented by a contribution that is nonlinear in the
Einstein-Hilbert term. While the addition of the nonlinear terms does not
affect the scalar modes of the geometry during the inflationary phase, the
tensor-to-scalar ratio is nonetheless suppressed. In this context it is
plausible to have a stiff phase following the standard inflationary stage
provided the potential has a quintessential form. The large-scale magnetic
fields can even be a fraction of the nG over typical length scales of the order
of the Mpc prior to the gravitational collapse of the protogalaxy.
