The cosmic microwave background temperature bispectrum from scalar perturbations induced by primordial magnetic fields

TL;DR

This paper calculates the CMB temperature bispectrum caused by primordial magnetic fields, revealing how non-Gaussianity depends on magnetic spectral index and setting bounds on magnetic field strength.

Contribution

It provides a detailed evaluation of the CMB bispectrum from primordial magnetic fields and derives new constraints on their amplitude based on non-Gaussianity measurements.

Findings

Bounds on magnetic field amplitude: ~10 nGauss for scale-invariant spectrum

Bispectrum shape peaks in squeezed configuration

Non-Gaussianity depends on magnetic spectral index

Abstract

We evaluate the angular bispectrum of the CMB temperature anisotropy at large angular scale due to a stochastic background of primordial magnetic fields. The shape of non-Gaussianity depends on the spectral index of the magnetic field power spectrum and is peaked in the squeezed configuration for a scale-invariant magnetic spectrum. By using the large angular part of the bispectrum generated by magnetic fields, the present bounds on non-Gaussianity set a limit on the amplitude of the primordial magnetic field of the order of 10 nGauss for the scale-invariant case and 20 nGauss for the other spectral indexes.