Massive Neutrinos and Magnetic Fields in the Early Universe

TL;DR

This paper analyzes how primordial magnetic fields and massive neutrinos influence the CMB, revealing that neutrino mass alters large-scale perturbations but with smaller effects than previously thought.

Contribution

It provides a systematic analysis of perturbations in the early universe considering magnetic fields and neutrino mass effects, including detailed calculations of CMB power spectra.

Findings

Massive neutrinos qualitatively change large-scale magnetic perturbations.

Neutrino mass effects on perturbations are smaller than previously claimed.

Calculated CMB spectra from primordial magnetic fields across different modes.

Abstract

Primordial magnetic fields and massive neutrinos can leave an interesting signal in the CMB temperature and polarization. We perform a systematic analysis of general perturbations in the radiation-dominated universe, accounting for any primordial magnetic field and including leading- order effects of the neutrino mass. We show that massive neutrinos qualitatively change the large- scale perturbations sourced by magnetic fields, but that the effect is much smaller than previously claimed. We calculate the CMB power spectra sourced by inhomogeneous primordial magnetic fields, from before and after neutrino decoupling, including scalar, vector and tensor modes, and consistently modelling the correlation between the density and anisotropic stress sources. In an appendix we present general series solutions for the possible regular primordial perturbations.