Critical constraint on inflationary magnetogenesis

Abstract

Recently, there are several reports that the cosmic magnetic fields on Mpc scalein void region is larger than ∼ 10−15G withan uncertainty of a few orders from the current blazar observations.On the other hand, in inflationary magnetogenesis models,additional primordial curvature perturbations are inevitably produced fromiso-curvature perturbationsdue to generated electromagnetic fields.We explore such induced curvature perturbationsin a model independent wayandobtained a severe upper bound for the energy scale of inflationfrom the observed cosmic magnetic fields andthe observed amplitude of the curvature perturbation, as ρinf1/4 < 300MeV × (Bobs/10−15G)−1 where Bobs is the strength of the magnetic field at present.Therefore, without a dedicated low energy inflation model oran additional amplification of magnetic fields after inflation,inflationary magnetogenesis on Mpc scaleis generally incompatible with CMB observations.