Evolution of hydromagnetic turbulence from the electroweak phase transition

TL;DR

This paper presents simulations of hydromagnetic turbulence during the early universe's electroweak phase, analyzing how initial helicity influences magnetic field evolution and potential present-day magnetic field strengths.

Contribution

It provides new insights into the decay laws of helical and nonhelical magnetic fields from early universe conditions, highlighting their relevance to cosmic magnetic field origins.

Findings

Helical fields become maximally helical over time with different decay laws.

Nonhelical magnetically dominated fields could produce picoGauss magnetic fields.

Helical magnetic fields may reach nanoGauss strengths at large scales today.

Abstract

We present new simulations of decaying hydromagnetic turbulence for a relativistic equation of state relevant to the early universe. We compare helical and nonhelical cases either with kinetically or magnetically dominated initial fields. Both kinetic and magnetic initial helicities lead to maximally helical magnetic fields after some time, but with different temporal decay laws. Both are relevant to the early universe, although no mechanisms have yet been identified that produce magnetic helicity with strengths comparable to the big bang nucleosynthesis limit at scales comparable to the Hubble horizon at the electroweak phase transition. Nonhelical magnetically dominated fields could still produce picoGauss magnetic fields under most optimistic conditions. Only helical magnetic fields can potentially have nanoGauss strengths at scales up to 30 kpc today.