Electric-magnetic duality and the conditions of inflationary magnetogenesis

TL;DR

This paper critically analyzes inflationary magnetogenesis driven by gauge coupling variations, emphasizing electric-magnetic duality, plasma conductivity effects, and conditions for generating large-scale magnetic fields.

Contribution

It provides explicit computations of power spectra using duality transformations and clarifies how plasma effects break this duality, impacting magnetogenesis models.

Findings

Electric-magnetic duality helps compute power spectra in source-free scenarios.

Post-inflationary conductivity breaks duality, affecting magnetic field generation.

Physical conditions for successful inflationary magnetogenesis are identified.

Abstract

The magnetogenesis scenarios triggered by the early variation of the gauge coupling are critically analyzed. In the absence of sources, it is shown that the electric and magnetic power spectra can be explicitly computed by means of electric-magnetic duality transformations. The remnants of a pre-inflationary expansion and the reheating process break explicitly electric-magnetic duality by inducing Ohmic currents. The generation of large-scale magnetic field and the physical distinction between electric and magnetic observables stems, in this class of models, from the final value reached by the conductivity of the plasma right after inflation. Specific numerical examples are given. The physical requirements of viable magnetogenesis scenarios are spelled out.