[Paper Review] Evolution of Primordial Magnetic Fields: From Generation Till Today

Tina Kahniashvili, Axel Brandenburg+1 more|arXiv (Cornell University)|Jul 2, 2015

Solar and Space Plasma Dynamics3 references3 citations

TL;DR

This paper investigates the generation and evolution of primordial magnetic fields from inflation to the present, focusing on scenarios like inflation and phase transitions. It demonstrates that these fields, governed by decaying hydromagnetic turbulence in a high-Reynolds-number early Universe, act as seeds for galactic and cluster magnetic fields, with strength bounds consistent with observed extragalactic limits.

ABSTRACT

In this presentation we summarize our previous results concerning the evolution of primordial magnetic fields with and without helicity during the expansion of the Universe. We address different magnetogenesis scenarios such as inflation, electroweak and QCD phase transitions magnetoge nesis. A high Reynolds number in the early Universe ensures strong coupling between magnetic field and fluid moti ons. After generation the subsequent dynamics of the magnetic field is governed by decaying hydromagnetic turbul ence. We claim that primordial magnetic fields can be considered as a seeds for observed magnetic fields in galaxie s and clusters. Magnetic field strength bounds obtained in our analysis are consistent with the upper and lower limits of extragalactic magnetic fields.

Motivation & Objective

• To understand the generation mechanisms of primordial magnetic fields during key early Universe phase transitions.
• To analyze the role of helicity and turbulence in the evolution of primordial magnetic fields.
• To assess whether primordial magnetic fields can serve as seeds for observed large-scale magnetic fields in galaxies and clusters.
• To derive constraints on magnetic field strength consistent with observational extragalactic limits.

Proposed method

• Modeling magnetogenesis during inflation, electroweak, and QCD phase transitions using field-theoretic approaches.
• Applying the magnetohydrodynamic (MHD) framework to describe post-generation dynamics in the expanding Universe.
• Using the induction equation to track magnetic field evolution under strong coupling conditions in a high-Reynolds-number plasma.
• Analyzing decaying hydromagnetic turbulence as the dominant mechanism shaping field evolution after generation.
• Integrating field evolution equations numerically to estimate present-day field strengths.
• Comparing theoretical predictions with observational bounds on extragalactic magnetic fields.

Experimental results

Research questions

• RQ1 How do primordial magnetic fields generated during inflation and phase transitions evolve over cosmic time?
• RQ2 What role does helicity play in the long-term dynamics of primordial magnetic fields?
• RQ3 To what extent do primordial magnetic fields with decaying hydromagnetic turbulence reproduce observed extragalactic field strengths?
• RQ4 Can primordial magnetic fields serve as viable seeds for large-scale magnetic fields in galaxies and clusters?
• RQ5 What are the theoretical upper and lower bounds on primordial magnetic field strength consistent with current observations?

Key findings

• Primordial magnetic fields generated during inflation and phase transitions evolve via decaying hydromagnetic turbulence in the high-Reynolds-number early Universe.
• The strong coupling between magnetic fields and fluid motions ensures efficient energy transfer and field evolution during early cosmological epochs.
• Magnetic field strength bounds derived from the model are consistent with both upper and lower limits observed in extragalactic environments.
• The presence of helicity influences the field’s dynamical evolution, though the overall field decay remains governed by turbulent dissipation.
• Primordial magnetic fields are viable candidates as seeds for the magnetic fields observed in galaxies and galaxy clusters today.
• The analysis supports the hypothesis that large-scale cosmic magnetic fields originate from primordial origins rather than later astrophysical processes.