Gravitational tensor and acoustic waves in a radiation dominated universe: Weyl curvature and polarization patterns

We provide evidence that gravitational radiation in a 4D radiation-dominated universe, with equation-of-state $w=1/3$, consists of two components: helicity-2 gravitons and massless scalar acoustic waves. On physical grounds, we would expect the homogeneous solution Weyl tensor components to be good approximation its inhomogeneous counterparts, whenever observer is located well far zone an isolated astrophysical source cosmological radiation. show explicitly these solutions both receive contributions from gauge-invariant {\it and} Bardeen (acoustic) scalars. Comparison computations thus allows us not only identify, high frequency limit, corresponding radiation; but also their oscillatory polarization patterns.