Polarized Cosmological Gravitational Waves from Primordial Helical Turbulence

We show that helical turbulence produced during a first-order phase transition generates circularly polarized cosmological gravitational waves (GWs). The characteristic frequency of these GWs for an extreme case of the phase transition model is around ${10}^{-3}$ — ${10}^{-2}$ Hz with an energy density parameter as high as ${10}^{-12}$ — ${10}^{-11}$. The possibility of detection is briefly discussed.