{lambda}{alpha}DM: Observational constraints on unified dark matter with constant speed of sound

Journal Article · Thu Nov 15 04:00:00 EST 2007 · Physical Review. D, Particles Fields

DOI:https://doi.org/10.1103/PHYSREVD.76.103519· OSTI ID:21027812

Balbi, Amedeo ^[1]; Bruni, Marco ^[1]; Quercellini, Claudia ^[1]

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1. Dipartimento di Fisica, Universita di Roma 'Tor Vergata', via della Ricerca Scientifica 1, 00133 Rome (Italy)

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=p{sub 0}+{alpha}{rho}, resulting in an effective cosmological constant {rho}{sub {lambda}}=-p{sub 0}/(1+{alpha}). 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({rho}), 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, {alpha} and {omega}{sub {lambda}}, using data from a suite of different cosmological observations, and perform a comparison with the standard {lambda}CDM 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 {lambda}CDM, with best-fit values {alpha}=0.01{+-}0.02 and {omega}{sub {lambda}}=0.70{+-}0.04 (95% confidence intervals). The standard model (best-fit {omega}{sub {lambda}}=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 {lambda}CDM. For the latter, the best-fit values are {omega}{sub K}=-0.02{sub -0.02}{sup +0.01} and {omega}{sub {lambda}}=0.71{+-}0.04, i.e. a closed model is preferred. A phantom UDM with affine EoS is ruled out well beyond 3{sigma}.

• OSTI ID: 21027812
• Journal Information: Physical Review. D, Particles Fields, Journal Name: Physical Review. D, Particles Fields Journal Issue: 10 Vol. 76; ISSN PRVDAQ; ISSN 0556-2821
• Country of Publication: United States
• Language: English

Related Subjects

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS
APPROXIMATIONS
COMPARATIVE EVALUATIONS
COSMOLOGICAL CONSTANT
COSMOLOGY
EQUATIONS OF STATE
MATHEMATICAL SOLUTIONS
NONLUMINOUS MATTER
PHANTOMS
POTENTIALS
SCALAR FIELDS
SOUND WAVES
STANDARD MODEL
VELOCITY