Generation of helical magnetic fields from inflation

The generation of helical magnetic fields during single field inflation due to an axial coupling of the electromagnetic field to the inflaton has been discussed. We have found that such a coupling always leads to a blue spectrum of magnetic fields during slow roll inflation. Though the helical magnetic fields further evolve during the inverse cascade in the radiation era after inflation, we have concluded that the magnetic fields generated by such an axial coupling can not lead to observed field strength on cosmologically relevant scales