2024/06/18 by Guillermo Palma, Palma, Guillermo, Gabriel Gómez +3
Neuroscience · Physics and Astronomy · #Cosmology and Gravitation Theories #Cosmology and Nongalactic Astrophysics (astro-ph.CO) #Dark Matter and Cosmic Phenomena #FOS: Physical sciences #Functional Brain Connectivity Studies #General Relativity and Quantum Cosmology (gr-qc)
paper · pdf · doi:10.48550/arxiv.2406.12724
openalex publication_date 2024/06/18 · openalex created_date 2025/10/10 · openalex updated_date 2026/07/28
Viscous unified dark matter models aim to describe the dark sector of the Universe, as the dark matter fluid itself gives rise to an accelerated expansion due to a negative bulk viscous pressure. However, in most studies, radiation is often disregarded as a minor factor in dynamical system analyses, overlooking whether radiation domination is achievable. In this paper, we rigorously examine this critical aspect for common parameterizations of bulk viscosity, denoted as ξ, within two general classes of viscous unified models. Our findings reveal significant inconsistencies in models where ξ∝ H1-2s ρms with s≤ 0, and surprisingly, in models where ξ∝ ρms with exponents s<0, as they both fail to produce a radiation-dominated era. Moreover, the exponent s must lye within the interval 0 ≤ s < 1/2 for the latter model to correctly describes the cosmological evolution. These results underscore the need of including these constraints as a prior in statistical analyses of observational data, with implications for current statistical inferences for the second model, where both prior and best-fit values of s often fall outside the acceptable range.