Numerical Simulations of Gravitational Waves from Early-Universe Turbulence

We perform direct numerical simulations of magnetohydrodynamic turbulence in the early universe
and numerically compute the resulting stochastic background of gravitational waves and relic
magnetic fields. We obtain kinetic and magnetic energy spectra with greater realism than earlier
analytic models. The computed gravitational wave spectra have a new universal form at low frequencies,
with more power than suggested by earlier analytical models. The efficiency of gravitational
wave production varies significantly with the physical form of the turbulence. For the same amount
of turbulent energy, we find that the gravitational wave signal is stronger for irrotational flows than
for vortical ones. Our results predict that a signal produced at the electroweak scale is detectable
by the planned Laser Interferometer Space Antenna if at least 1% of the total energy density is
injected into magnetic fields or turbulent plasma motions.

https://arxiv.org/abs/1903.08585
https://arxiv.org/abs/1807.05479