Simulating Relic Gravitational Waves from Inflationary Magnetogenesis

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 0.03% and 0.5% 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.

Automated summary

A study using three-dimensional simulations investigates the production of magnetic fields and gravitational waves in the early universe, finding that turbulence may not be as effective in driving gravitational waves as previously thought. Magnetic energy densities are found to be between 0.03% and 0.5% of the critical energy density at the end of reheating, with gravitational wave spectra extending to higher frequencies in specific models with reheating temperatures around 100 GeV during the early radiation-dominated era.