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 of the Weyl tensor components to be a
good approximation to its inhomogeneous counterparts, whenever the observer is
located well in the far zone of an isolated astrophysical source of
cosmological gravitational radiation. We show explicitly that these homogeneous
and inhomogeneous solutions both receive contributions from the gauge-invariant
tensor {\it and} the two Bardeen (acoustic) scalars. Comparison of these Weyl
tensor computations thus allows us to not only identify, in the high frequency
limit, the corresponding gravitational tensor and scalar radiation; but also
their oscillatory polarization patterns.
