Pre-reheating Magnetogenesis in the Kinetic Coupling Model

TL;DR

This paper investigates a post-inflationary magnetogenesis model involving a kinetically coupled scalar field, demonstrating it can generate observable magnetic fields without conflicting with CMB constraints.

Contribution

It introduces a novel magnetogenesis scenario with a non-inflaton field coupled kinetically to electromagnetism, validated against backreaction and CMB constraints.

Findings

Successful magnetic field generation without low-scale inflation

Explicit verification of backreaction constraints

Compatibility with CMB scalar fluctuation limits

Abstract

Recent blazar observations provide growing evidence for the presence of magnetic fields in the extragalactic regions. While a natural speculation is to associate the production to inflationary physics, it has been known that magnetogenesis solely from inflation is quite challenging. We therefore study a model in which a non-inflaton field $\chi$ coupled to the electromagnetic field through its kinetic term, $-I^2(\chi) F^2 /4$, continues to move after inflation until the completion of reheating. This leads to a post-inflationary amplification of the electromagnetic field. We compute all the relevant contributions to the curvature perturbation, including gravitational interactions, and impose the constraints from the CMB scalar fluctuations on the strength of magnetic fields. We, for the first time, explicitly verify both the backreaction and CMB constraints in a simple yet successful magnetogenesis scenario without invoking a dedicated low-scale inflationary model in the weak-coupling regime of the kinetic coupling model.