Gauge-invariant analysis of perturbations in Chaplygin gas unified models of dark matter and dark energy

Journal Article · Fri Feb 15 04:00:00 EST 2008 · Journal of Cosmology and Astroparticle Physics

DOI:https://doi.org/10.1088/1475-7516/2008/02/016· OSTI ID:22137792

Gorini, V; Moschella, U; Piattella, O F ^[1]; Kamenshchik, A Y ^[2]

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1. Dipartimento di Scienze Fisiche e Matematiche, Universita dell'Insubria, Via Valleggio 11, I-22100 Como (Italy)
2. Dipartimento di Fisica and INFN, Via Irnerio 46, I-40126 Bologna (Italy)

We exploit the gauge-invariant formalism to analyse the perturbative behaviour of two cosmological models based on the generalized Chaplygin gas describing both dark matter and dark energy in the present universe. In the first model we consider the generalized Chaplygin gas alone, while in the second one we add a baryon component to it. We extend our analysis also into the parameter range {alpha}>1, where the generalized Chaplygin gas sound velocity can be larger than that of light. In the first model we find that the matter power spectrum is compatible with the observed one only for {alpha}<10{sup -5}, which makes the generalized Chaplygin gas practically indistinguishable from {Lambda}CDM. In the second model we study the evolution of inhomogeneities of the baryon component. The theoretical power spectrum is in good agreement with the observed one for almost all values of {alpha}. However, the growth of inhomogeneities seems to be particularly favoured either for sufficiently small values of {alpha} or for {alpha}{approx}>3. Thus, it appears that the viability of the generalized Chaplygin gas as a cosmological model is stronger when its sound velocity is superluminal. We show that in this case the generalized Chaplygin gas equation of state can be changed in an unobservable region in such a way that its equivalent k-essence microscopical model has no problems with causality.

• OSTI ID: 22137792
• Journal Information: Journal of Cosmology and Astroparticle Physics, Journal Name: Journal of Cosmology and Astroparticle Physics Journal Issue: 02 Vol. 2008; ISSN 1475-7516
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTRONOMY AND ASTROPHYSICS
BARYONS
CAUSALITY
COSMOLOGICAL MODELS
DISTURBANCES
EQUATIONS OF STATE
GAUGE INVARIANCE
MATHEMATICAL EVOLUTION
NONLUMINOUS MATTER
SOUND WAVES
SPECTRA
UNIFIED MODEL
UNIVERSE
VELOCITY
VISIBLE RADIATION