Does bulk viscosity create a viable unified dark matter model?

Journal Article · Fri May 15 04:00:00 EDT 2009 · Physical Review. D, Particles Fields

DOI:https://doi.org/10.1103/PHYSREVD.79.103521· OSTI ID:21296325

Baojiu, Li; Barrow, John D ^[1]

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1. DAMTP, Centre for Mathematical Sciences, University of Cambridge, Cambridge CB3 0WA (United Kingdom)

We investigate in detail the possibility that a single imperfect fluid with bulk viscosity can replace the need for separate dark matter and dark energy in cosmological models. With suitable choices of model parameters, we show that the background cosmology in this model can mimic that of a {lambda}CDM universe to high precision. However, as the cosmic expansion goes through the decelerating-accelerating transition, the density perturbations in this fluid are rapidly damped out. We show that, although this does not significantly affect structure formation in baryonic matter, it makes the gravitational potential decay rapidly at late times, leading to modifications in predictions of cosmological observables such as the CMB power spectrum and weak lensing. This model of unified dark matter is thus difficult to reconcile with astronomical observations. We also clarify the differences with respect to other unified dark matter models where the fluid is barotropic, i.e., p=p({rho}), such as the (generalized) Chaplygin gas model, and point out their observational difficulties. We also summarize the status of dark sector models with no new dynamical degrees of freedom introduced and discuss the problems with them.

• OSTI ID: 21296325
• Journal Information: Physical Review. D, Particles Fields, Journal Name: Physical Review. D, Particles Fields Journal Issue: 10 Vol. 79; ISSN PRVDAQ; ISSN 0556-2821
• Country of Publication: United States
• Language: English

Related Subjects

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS
BARYONS
COSMOLOGICAL MODELS
COSMOLOGY
DECAY
DEGREES OF FREEDOM
DENSITY
DISTURBANCES
EXPANSION
FORECASTING
MODIFICATIONS
NONLUMINOUS MATTER
PERTURBATION THEORY
SPECTRA
UNIVERSE