The scalar, vector, and tensor modes in gravitational wave turbulence simulations

Abstract

We study the gravitational wave (GW) signal sourced by primordial turbulence that is assumed to be present at cosmological phase transitions like the electroweak and quantum chromodynamics phase transitions. We consider various models of primordial turbulence, such as those with and without helicity, purely hydrodynamical turbulence induced by fluid motions, and magnetohydrodynamic turbulence whose energy can be dominated either by kinetic or magnetic energy, depending on the nature of the turbulence. We also study circularly polarized GWs generated by parity violating sources such as helical turbulence. Our ultimate goal is to determine the efficiency of GW production through different classes of turbulence. We find that the GW energy and strain tend to be large for acoustic or irrotational turbulence, even though its tensor mode amplitude is relatively small at most wave numbers. Only at very small wave numbers is the spectral tensor mode significant, which might explain the efficient GW production in that case.

Simulating relic gravitational waves from inflationary magnetogenesis

“…The GW energy of our runs scales approximately quadratically with magnetic energy. Following earlier work (Roper Pol et al 2020b;Brandenburg et al 2021b) we confirm a relation of the form E GW = (qE M /k c ) 2 , where q is the efficiency and k c is the characteristic wavenumber, for which the value k c = k * (1) has been used. The values of E M range between 0.002 and 0.02, corresponding to magnetic energy densities between 0.2% and 2% of the radiation energy density.…”

Big Bang Nucleosynthesis Limits and Relic Gravitational Waves Detection Prospects

“…As already noted in previous studies [11,12,44], the GW energy spectrum from forced turbulence shows almost no or a rapidly declining inertial range for frequencies above the peak. This is because only the smallest wave numbers contribute significantly to the driving of GWs [44,68]. In fact, the GW energy h 2 0 Ω GW (f phys ) scales approximately quadratically with the ratio of magnetic energy to characteristic wave number k 0 as (qE M /k 0 ) 2 , where q is the efficiency (of order unity).…”