Affine parametrization of the dark sector: Constraints from WMAP5 and SDSS

Journal Article · Wed Oct 15 04:00:00 EDT 2008 · Physical Review. D, Particles Fields

DOI:https://doi.org/10.1103/PHYSREVD.78.083510· OSTI ID:21254394

Pietrobon, Davide; Bruni, Marco ^[1]; Balbi, Amedeo ^[2]; Quercellini, Claudia ^[2]

---

1. Institute of Cosmology and Gravitation, University of Portsmouth, Mercantile House, Portsmouth PO1 2EG (United Kingdom)
2. Dipartimento di Fisica, Universita di Roma 'Tor Vergata', via della Ricerca Scientifica 1, 00133 Roma (Italy)

We study a set of universe models where the dark sector is described by a perfect fluid with an affine equation of state P=P{sub 0}+{alpha}{rho}, focusing specifically on cosmological perturbations in a flat universe. We perform a Monte Carlo Markov Chain analysis spanning the full parameter space of the model using the WMAP 5-yr data and the SDSS LRG4 survey. The affine fluid can either play the role of a unified dark matter, accounting for both dark matter and a cosmological constant, or work alongside cold dark matter (CDM), as a form of dark energy. A key ingredient is the sound speed, that depends on the nature of the fluid and that, for any given background model, adds a degree of freedom to the perturbations: in the barotropic case the square of the sound speed is simply equal to the affine parameter {alpha}; if entropic perturbations are present the effective sound speed has to be specified as an additional parameter. In addition to the barotropic case, we consider the two limiting cases of effective sound speed equal to 0 or 1. For {alpha}=c{sub s}{sup 2}=0 our unified dark matter model is equivalent to the standard {lambda}CDM with adiabatic perturbations. Apart of a trivial subcase, all models considered satisfy the data constraints, with quite standard values for the usual cosmological parameters. In general our analysis confirms that cosmological data sets require both a collisionless massive and cold component to form the potential wells that lead to structure formation, and an effective cosmological constant that drives the late accelerated expansion.

• OSTI ID: 21254394
• Journal Information: Physical Review. D, Particles Fields, Journal Name: Physical Review. D, Particles Fields Journal Issue: 8 Vol. 78; ISSN PRVDAQ; ISSN 0556-2821
• Country of Publication: United States
• Language: English

Related Subjects

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS
COSMOLOGICAL CONSTANT
DEGREES OF FREEDOM
DISTURBANCES
EQUATIONS OF STATE
EXPANSION
FLUIDS
FOCUSING
IDEAL FLOW
MARKOV PROCESS
MONTE CARLO METHOD
NONLUMINOUS MATTER
PERTURBATION THEORY
POTENTIALS
SOUND WAVES
SPACE
UNIVERSE