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"Understanding" cosmological bulk viscosity

Winfried Zimdahl

astro-pharXiv:astro-ph/9602128

Abstract

A universe consisting of two interacting perfect fluids with the same 4-velocity is considered. A heuristic mean free time argument is used to show that the system as a whole cannot be perfect as well but neccessarily implies a nonvanishing bulk viscosity. A new formula for the latter is derived and compared with corresponding results of radiative hydrodynamics.

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