Intrinsic Bispectra of Cosmic Magnetic Fields

TL;DR

This paper analyzes the intrinsic bispectra of early-universe magnetic fields to understand their potential contribution to CMB non-Gaussianity, aiding in distinguishing inflationary signals from magnetic field effects.

Contribution

It provides a detailed calculation of the intrinsic bispectra for various power-law magnetic spectra, a novel step in modeling magnetic field impacts on CMB non-Gaussianity.

Findings

Intrinsic bispectra depend on magnetic spectral index.

Magnetic fields can produce measurable non-Gaussian signals.

Results help differentiate magnetic effects from inflationary non-Gaussianity.

Abstract

Forthcoming datasets from the Planck experiment and others are in a position to probe the CMB non-Gaussianity with higher accuracy than has yet been possible and potentially open a new window into the physics of the very early universe. However, a signal need not necessarily be inflationary in origin, and possible contaminants should be examined in detail. One such is provided by early universe magnetic fields, which can be produced by a variety of models including during an inflationary phase, at phase transitions, or seeded by cosmic defects. Should such fields have been extent in the early universe they provide a natural source of CMB non-Gaussianity. Knowledge of the CMB angular bispectrum requires the complete Fourier-space (or "intrinsic") bispectrum. In this paper I consider in detail the intrinsic bispectra of an early-universe magnetic field for a range of power-law magnetic power spectra.