Void magnetic field and its primordial origin in inflation

Since magnetic fields in galaxies, galactic clusters and even void regions are observed, theoretical attempts to explain their origin are strongly motivated. It is interesting to consider that inflation is responsible for the origin of the magnetic fields as well as the density perturbation. However, it is known that inflationary magnetogenesis suffers from several problems. We explore these problems by using a specific model, namely the kinetic coupling model, and show how the model is constrained. Model independent arguments are also discussed.Comment: 7 pages, 1 figure, v2: reference updated, to appear in the proceedings of The 10th International Symposium on Cosmology and Particle Astrophysics (CosPA2013

Critical constraint on inflationary magnetogenesis

Recently, there are several reports that the cosmic magnetic fields on Mpc scale in void region is larger than $\sim 10^{-15}$G with an 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 from iso-curvature perturbations due to generated electromagnetic fields. We explore such induced curvature perturbations in a model independent way and obtained a severe upper bound for the energy scale of inflation from the observed cosmic magnetic fields and the observed amplitude of the curvature perturbation, as $\rho_{\rm inf}^{1/4} < 30{\rm GeV} \times (B_{\rm obs}/10^{-15}{\rm G})^{-1}$ where $B_{\rm obs}$ is the strength of the magnetic field at present. Therefore, without a dedicated low energy inflation model or an additional amplification of magnetic fields after inflation, inflationary magnetogenesis on Mpc scale is generally incompatible with CMB observations.Comment: 16 pages, 1 figure, references added, a numerical error fixed. Accepted for publication in JCA