Simulating relic gravitational waves from inflationary magnetogenesis

TL;DR

This paper uses 3D simulations to explore how magnetic fields and gravitational waves are produced during early Universe reheating, revealing that turbulence influences GW spectra and their detectability.

Contribution

It provides the first detailed numerical analysis of magnetic field and GW production during post-inflationary reheating with turbulence effects.

Findings

Magnetic energy densities reach 0.2% to 2% of critical density.

GW spectra extend to millihertz and nanohertz frequencies.

Turbulence reduces GW production efficiency at high frequencies.

Abstract

We present three-dimensional direct numerical simulations of the production of magnetic fields and gravitational waves (GWs) in the early Universe during a low energy scale matter-dominated post-inflationary reheating era, and during the early subsequent radiative era, which is strongly turbulent. The parameters of the model are determined such that it avoids a number of known physical problems and produces magnetic energy densities between 0.2% and 2% of the critical energy density at the end of reheating. During the subsequent development of a turbulent magnetohydrodynamic cascade, magnetic fields and GWs develop a spectrum that extends to higher frequencies in the millihertz (nanohertz) range for models with reheating temperatures of around 100 GeV (150 MeV) at the beginning of the radiation-dominated era. However, even though the turbulent cascade is fully developed, the GW spectrum shows a sharp drop for frequencies above the peak value. This suggests that the turbulence is less efficient in driving GWs than previously thought. The peaks of the resulting GW spectra may well be in the range accessible to space interferometers, pulsar timing arrays, and other facilities.