Cosmological consequences of first-order general-relativistic viscous fluid dynamics

Abstract

We investigate the out-of-equilibrium dynamics of viscous fluids in a spatially flat Friedmann-Lemaître-Robertson-Walker cosmology using the most general causal and stable viscous energy-momentum tensor defined at first order in spacetime derivatives. In this new framework a pressureless viscous fluid having density $\rho$ can evolve to an asymptotic future solution in which the Hubble parameter approaches a constant while $\rho \to 0$, even in the absence of a cosmological constant (i.e., $\Lambda =0$). Thus, while viscous effects in this model drive an accelerated expansion of the universe, the density of the viscous component itself vanishes, leaving behind only the acceleration. This behavior emerges as a consequence of causality in first-order theories of relativistic fluid dynamics and it is fully consistent with Einstein's equations.

14 pages, no figures, references updated, discussion added

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• Radial Oscillations of Viscous Neutron Stars: Zero Diffusion Case