## 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 equilibrium energy density ρ can evolve to an asymptotic future solution in which the Hubble parameter approaches a constant while ρ→0, even in the absence of a cosmological constant (i.e., Λ=0). Thus, while viscous effects in this model drive an accelerated expansion of the universe, the equilibrium energy density 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.

Original language | English (US) |
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Article number | 023512 |

Journal | Physical Review D |

Volume | 107 |

Issue number | 2 |

DOIs | |

State | Published - Jan 15 2023 |

Externally published | Yes |

## ASJC Scopus subject areas

- Nuclear and High Energy Physics