On the Generation of Sound from the Primordial Turbulence in an Expanding Universe

概要

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In order that galaxies may be formed from the primordial turbulence in a big-bang universe, the cosmic turbulence with suitable scales must survive up to the decoupling. epoch of matter from radiation against its decay due to the generation of sound as envisaged by Lighthill and Crighton. To attack the problem with due consideration of the effect of cosmic expansion neglected in the Lighthill-Crighton theory, the generation of sound from the cosmic turbulence is dealt with by constructing the appropriate retarded Green's function in which all significant influences of the cosmic expansion upon the propagation of sound waves to be generated are woven. It is shown that the expanding turbulent fluid is inevitably of a diffusive nature in such a way that its physical radius is equal to the acoustical event horizon. The latter situation means that the retardation effect is essential in the evaluation of the intensity of sound at the center of the turbulent fluid sphere, while the effect was discarded in the Crighton formula for a static diffusive medium. In other words, our formalism is superior to Crighton's for the examination of the aforementioned problem.
理論物理学刊行会の論文
1973-08-25