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

TL;DR

This paper investigates how different models of primordial turbulence during cosmological phase transitions generate gravitational waves, analyzing their efficiency and spectral characteristics across various turbulence types.

Contribution

It provides a comprehensive analysis of GW production from diverse primordial turbulence models, including helical and magnetohydrodynamic turbulence, with insights into their spectral tensor modes.

Findings

Acoustic turbulence produces large GW energy and strain.

Tensor mode amplitude is small except at very small wave numbers.

Spectral tensor mode becomes significant at very small wave numbers.

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.