Magnetogenesis, spectator fields and CMB signatures

TL;DR

This paper explores a class of magnetogenesis models involving spectator fields coupled to hypercharge, analyzing their impact on CMB signatures and the potential for generating observable magnetic fields.

Contribution

It introduces a viable magnetogenesis model linking magnetic power spectra to curvature inhomogeneities, with implications for CMB observations and galactic magnetic fields.

Findings

Magnetic fields of 0.01--0.1 nG can be generated at galaxy formation epoch.

Magnetic contributions to CMB anisotropies are consistent with observational constraints.

The model provides insights into the interplay between magnetogenesis and CMB signatures.

Abstract

A viable class of magnetogenesis models can be constructed by coupling the kinetic term of the hypercharge to a spectator field whose dynamics does not affect the inflationary evolution. The magnetic power spectrum is explicitly related to the power spectrum of (adiabatic) curvature inhomogeneities when the quasi-de Sitter stage of expansion is driven by a single scalar degree of freedom. Depending upon the value of the slow-roll parameters, the amplitude of smoothed magnetic fields over a (comoving) Mpc scale can be as large as 0.01--0.1 nG at the epoch of the gravitational collapse of the protogalaxy. The contributions of the magnetic fields to the Sachs-Wolfe plateau and to the temperature autocorrelations in the Doppler region compare favourably with the constraints imposed by galactic magnetogenesis. Stimulating lessons are drawn on the interplay between magnetogenesis models and their possible CMB signatures.