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

TL;DR

This paper investigates how certain inflationary models can generate seed magnetic fields strong enough to explain galactic magnetism, highlighting the conditions under which these fields become astrophysically significant.

Contribution

It demonstrates that in (R/m^2)^n and I F^2 models, magnetic fields can be sufficiently amplified during inflation for n ≥ 2, especially with specific parameter choices, advancing understanding of cosmic magnetogenesis.

Findings

Magnetic fields are negligible if m equals the electron mass.

For n ≥ 2, fields can seed dynamo mechanisms and explain galactic magnetism.

Almost scale-invariant fields during near de Sitter inflation can directly account for microgauss galactic magnetic fields.

Abstract

We re-analyze the production of seed magnetic fields during Inflation in (R/m^2)^n F_{\mu \nu}F^{\mu \nu} and I F_{\mu \nu}F^{\mu \nu} models, where n is a positive integer, R the Ricci scalar, m a mass parameter, and I \propto \eta^\alpha a power-law function of the conformal time \eta, with \alpha a 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 \alpha \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 (\alpha \simeq 4), their intensity can be strong enough to directly explain the presence of microgauss galactic magnetic fields.