# Large scale magnetic fields from gravitationally coupled electrodynamics

## TL;DR

This paper investigates the generation of primordial magnetic fields during inflation through a curved spacetime coupling in electrodynamics, showing that significant magnetic seed fields can be produced to explain galactic magnetism.

## Contribution

It introduces a model based on the one-loop vacuum polarization effective action that couples curvature to the electromagnetic field during inflation, providing a mechanism for magnetic seed field generation.

## Key findings

- Magnetic fields of cosmologically relevant strength can be generated during inflation.
- The model's parameter space can produce seed fields sufficient for galactic magnetic fields.
- The results are consistent with bounds required for seeding galactic magnetism.

## Abstract

The generation of primordial magnetic seed fields during inflation is studied in a theory derived from the one-loop vacuum polarization effective action of the photon in a curved background. This includes terms which couple the curvature to the Maxwell tensor. The resulting magnetic field strength is estimated in a model where the inflationary phase is directly matched to the standard radiation dominated era. The allowed parameter region is analyzed and compared with the bounds necessary to seed the galactic magnetic field. It is found that magnetic fields of cosmologically interesting field strengths can be generated.