Polarized Gravitational Waves from Cosmological Phase Transitions

TL;DR

The paper develops a formalism to quantify circular polarization in gravitational waves produced by first-order cosmological phase transitions (EWPT and QCDPT) driven by helical kinetic and magnetic turbulence. By extending helically-informed turbulence models and using an aero-acoustic approach, it derives the GW energy density and the polarization degree $P_{\rm GW}(k)=\mathcal{H}(k)/H(k)$, showing that polarization can reach unity for maximally helical sources near $k\approx 2k_0$ and depends on the helicity parameters. The work provides predictions for peak frequencies from direct and inverse cascade stages and offers a framework to interpret future GW observations (e.g., LISA/eLISA) for CP-violating signatures from the early universe. This advances the prospects of using polarized stochastic GW backgrounds as probes of early-universe magnetogenesis and turbulence.

Abstract

We estimate the degree of circular polarization for the gravitational waves generated during the electroweak and QCD phase transitions from the kinetic and magnetic helicity generated by bubble collisions during those cosmological phase transitions.

Figures (1)

• Figure 1: The GW polarization degree ${\mathcal{P}}^{\rm GW}(K)$ ($K=k/k_0$) in terms of the model parameter $h=1.0$, $0.5$, $0.1$