The Search for a Primordial Magnetic Field

TL;DR

This paper reviews the theoretical models and observational efforts to detect primordial magnetic fields, discussing their potential influence on cosmological phenomena and summarizing current constraints and future prospects.

Contribution

It provides a comprehensive overview of models and observational techniques for primordial magnetic fields, highlighting recent constraints and future research directions.

Findings

Current constraints on PMF amplitude and spectral index

Framework for calculating PMF effects on CMB and structure

Prospects for improved measurements of PMF properties

Abstract

Magnetic fields appear wherever plasma and currents can be found. As such, they thread through all scales in Nature. It is natural, therefore, to suppose that magnetic fields might have been formed within the high temperature environments of the big bang. Such a primordial magnetic field (PMF) would be expected to arise from and/or influence a variety of cosmological phenomena such as inflation, cosmic phase transitions, big bang nucleosynthesis, the cosmic microwave background (CMB) temperature and polarization anisotropies, the cosmic gravity wave background, and the formation of large-scale structure. In this review, we summarize the development of theoretical models for analyzing the observational consequences of a PMF. We also summarize the current state of the art in the search for observational evidence of a PMF. In particular we review the framework needed to calculate the effects of a PMF power spectrum on the CMB and the development of large scale structure. We summarize the current constraints on the PMF amplitude $B_\lambda$ and the power spectral index $n_B$ and discuss prospects for better determining these quantities in the near future.