Two-fluid cosmological models

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Abstract
Homogeneous and isotropic, relativistic two-fluid cosmological models are investigated. In these models two separate fluids act as the source of the gravitational field, as represented by the FRW line element. The general theory of two-fluid FRW models in which neither fluid need be comoving or perfect is developed. However, attention is focused on the physically interesting special class of flat FRW models in which one fluid is a comoving radiative perfect fluid and the second a noncomoving imperfect fluid. The first fluid is taken to model the cosmic microwave background and the second to model the observed material content of the universe. One of the motivations of the present work is to model the observed velocity of our galaxy relative to the cosmic microwave background that was recently discovered by G. F. Smoot, M. V. Gorenstein, and R. A. Muller [Phys. Rev. Lett. 39, 898 (1977)]. Several models within this special class are found and analyzed. The models obtained are theoretically satisfactory in that they are represented by solutions of Einstein’s field equations and the laws of thermodynamics in which all the physical quantities occurring in the solutions are suitably well behaved. In addition, the models are in agreement with current observations. Consequently it is believed that the models obtained are physically acceptable models of the universe.