Progress on Cosmological Magnetic Fields

TL;DR

This paper reviews the current observational constraints and theoretical implications of cosmological magnetic fields, their origins during early universe phase transitions, and the potential for particle physics experiments to test related CP violation.

Contribution

It synthesizes observational data, theoretical models, and experimental prospects concerning the origin and evolution of cosmic magnetic fields and their connection to fundamental particle interactions.

Findings

Magnetic fields in the universe are constrained between 10^{-16} and nano Gauss levels.

Magnetic helicity's evolution depends on early universe symmetry violations.

Accelerator experiments can test CP violation related to magnetic helicity generation.

Abstract

A variety of observations impose upper limits at the nano Gauss level on magnetic fields that are coherent on inter-galactic scales while blazar observations indicate a lower bound $\sim 10^{-16}$ Gauss. Such magnetic fields can play an important astrophysical role, for example at cosmic recombination and during structure formation, and also provide crucial information for particle physics in the early universe. Magnetic fields with significant energy density could have been produced at the electroweak phase transition. The evolution and survival of magnetic fields produced on sub-horizon scales in the early universe, however, depends on the magnetic helicity which is related to violation of symmetries in fundamental particle interactions. The generation of magnetic helicity requires new CP violating interactions that can be tested by accelerator experiments via decay channels of the Higgs particle.