Inflation-Produced Magnetic Fields in R^n F^2 and I F^2 models

Abstract

We re-analyze the production of seed magnetic fields during Inflation in (R/m^2)^n F_{μν}F^{μν} and I F_{μν}F^{μν} models, where n is a positive integer, R the Ricci scalar, m a mass parameter, and I \propto η^αa power-law function of the conformal time η, with αa positive real number. If m is the electron mass, the produced fields are uninterestingly small for all n. Taking m as a free parameter we find that, for n \geq 2, the produced magnetic fields can be sufficiently strong in order to seed dynamo mechanism and then to explain galactic magnetism. For α\gtrsim 2, there is always a window in the parameters defining Inflation such that the generated magnetic fields are astrophysically interesting. Moreover, if Inflation is (almost) de Sitter and the produced fields almost scale-invariant (α\simeq 4), their intensity can be strong enough to directly explain the presence of microgauss galactic magnetic fields.