ΛαDM: Observational constraints on unified dark matter with constant speed of sound

Amedeo Balbi, Marco Bruni, and Claudia Quercellini
Phys. Rev. D 76, 103519 – Published 12 November 2007

Abstract

We consider the hypothesis that dark energy and dark matter are the two faces of a single dark component, a unified dark matter (UDM) that we assume can be modeled by the affine equation of state (EoS) P=p0+αρ, resulting in an effective cosmological constant ρΛ=p0/(1+α). The affine EoS arises from the simple assumption that the speed of sound is constant; it may be seen as an approximation to an unknown barotropic EoS P=P(ρ), and may as well represent the tracking solution for the dynamics of a scalar field with appropriate potential. Furthermore, in principle the affine EoS allows the UDM to be phantom. We constrain the parameters of the model, α and ΩΛ, using data from a suite of different cosmological observations, and perform a comparison with the standard ΛCDM model, containing both cold dark matter and a cosmological constant. First considering a flat cosmology, we find that the UDM model with affine EoS fits the joint observations very well, better than ΛCDM, with best-fit values α=0.01±0.02 and ΩΛ=0.70±0.04 (95% confidence intervals). The standard model (best-fit ΩΛ=0.71±0.04), having one less parameter, is preferred by a Bayesian model comparison. However, the affine EoS is at least as good as the standard model if a flat curvature is not assumed as a prior for ΛCDM. For the latter, the best-fit values are ΩK=0.020.02+0.01 and ΩΛ=0.71±0.04, i.e. a closed model is preferred. A phantom UDM with affine EoS is ruled out well beyond 3σ.

  • Figure
  • Figure
  • Figure
  • Figure
  • Received 15 February 2007

DOI:https://doi.org/10.1103/PhysRevD.76.103519

©2007 American Physical Society

Authors & Affiliations

Amedeo Balbi1,2, Marco Bruni1,2,3, and Claudia Quercellini1

  • 1Dipartimento di Fisica, Università di Roma “Tor Vergata”, via della Ricerca Scientifica 1, 00133 Roma, Italy
  • 2INFN Sezione di Roma “Tor Vergata”, via della Ricerca Scientifica 1, 00133 Roma, Italy
  • 3Institute of Cosmology and Gravitation, University of Portsmouth, Mercantile House, Portsmouth PO1 2EG, United Kingdom

Article Text (Subscription Required)

Click to Expand

References (Subscription Required)

Click to Expand
Issue

Vol. 76, Iss. 10 — 15 November 2007

Reuse & Permissions
Access Options
Author publication services for translation and copyediting assistance advertisement

Authorization Required


×
×

Images

×

Sign up to receive regular email alerts from Physical Review D

Log In

Cancel
×

Search


Article Lookup

Paste a citation or DOI

Enter a citation
×