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.

Automated summary

The study analyzes large-scale magnetogenesis within the Palatini approach, finding that the addition of nonlinear terms can suppress the tensor-to-scalar ratio. A stiff phase may follow the standard inflationary stage if the potential has a quintessential form.