Phase-Space Constraints on a General Class of Eckart-like Viscous Cosmologies
Abstract
We study the cosmological dynamics of a general class of viscous dark matter models using a dynamical system analysis. In the Eckart formalism, these viscous cosmologies are characterized by a dimensionless bulk viscous pressure ΩΠ≡ ΩΠ(Ωm), where Ωm is the matter density parameter. Our analysis demonstrates that a viable early radiation era requires the complete absence of viscosity, a proper matter-dominated epoch demands a small viscous pressure, and the only physically admissible late-time attractor is the cosmological constant-dominated fixed point; consequently, the background expansion must closely track standard ΛCDM evolution. We validate these general results using the power-law parameterization ΩΠ= −ξ̂0 Ωms, where ξ̂0 and s are real parameters; for s ≥ 1 and ξ̂0 ≪ 1, the model reproduces the ΛCDM background, while for s < 1 the system encounters a past-time integration boundary where the dark matter density transitions into negative values and its viscous pressure evaluates to nonphysical complex numbers. Since the background expansion essentially duplicates ΛCDM, the model is unlikely to resolve the H0 tension. However, large differences arise at the linear perturbative level; indeed, on sub-horizon scales, bulk viscosity causes a scale-dependent dissipative drag on the matter density fluctuations; this increases the Hubble friction, offering a channel to suppress structure growth.
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BibTeX
@misc{moreno2026phasespace,
title = {{Phase-Space Constraints on a General Class of Eckart-like Viscous Cosmologies}},
author = {David R. Moreno and J. Bayron Orjuela-Quintana and Yeinzon Rodriguez},
howpublished = {arXiv},
year = {2026},
month = oct,
doi = {10.48550/arxiv.2610.35405},
eprint = {2610.35405},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2610.35405},
}
RIS
TY - UNPB
TI - Phase-Space Constraints on a General Class of Eckart-like Viscous Cosmologies
AU - David R. Moreno
AU - J. Bayron Orjuela-Quintana
AU - Yeinzon Rodriguez
PY - 2026
DA - 2026/10/26
PB - arXiv
DO - 10.48550/arxiv.2610.35405
UR - https://arxiv.org/abs/2610.35405
AB - We study the cosmological dynamics of a general class of viscous dark matter models using a dynamical system analysis. In the Eckart formalism, these viscous cosmologies are characterized by a dimensionless bulk viscous pressure Ω_Π≡ Ω_Π(Ω_m), where Ω_m is the matter density parameter. Our analysis demonstrates that a viable early radiation era requires the complete absence of viscosity, a proper matter-dominated epoch demands a small viscous pressure, and the only physically admissible late-time attractor is the cosmological constant-dominated fixed point; consequently, the background expansion must closely track standard ΛCDM evolution. We validate these general results using the power-law parameterization Ω_Π= −ξ̂_0 Ω_m^s, where ξ̂_0 and s are real parameters; for s ≥ 1 and ξ̂_0 ≪ 1, the model reproduces the ΛCDM background, while for s < 1 the system encounters a past-time integration boundary where the dark matter density transitions into negative values and its viscous pressure evaluates to nonphysical complex numbers. Since the background expansion essentially duplicates ΛCDM, the model is unlikely to resolve the H_0 tension. However, large differences arise at the linear perturbative level; indeed, on sub-horizon scales, bulk viscosity causes a scale-dependent dissipative drag on the matter density fluctuations; this increases the Hubble friction, offering a channel to suppress structure growth.
ER -