Extended family of generalized Chaplygin gas models

Journal of Cosmology and Astroparticle Physics, 2004

The hypothesis that dark matter and dark energy are unified through the Chaplygin gas, an exotic fluid obeying p = −A/ρ, is reexamined. Using generalizations of the spherical model which incorporate effects of the acoustic horizon we show that an initially perturbative Chaplygin gas evolves into a mixed system containing cold dark matter like gravitational condensate.

Dark Matter in Astro- and Particle Physics, 2002

We formulate a Zel'dovich-like approximation for the Chaplygin gas equation of state P = −A/ρ, and sketch how this model unifies dark matter with dark energy in a geometric setting reminiscent of M -theory. † Permanent address: Rudjer Bošković Institute,

2007

We present a holographic dark energy model of the universe considering modified extension of the generalized Chaplygin gas (GCG). The modified GCG behaves as an ordinary barotropic fluid in the early epoch when the universe was tiny but behaves subsequently as a ΛCDM model as the universe grows. We determine the corresponding holographic dark energy field and its potential. The stability of the holographic dark energy in this case is also discussed.

The generalized Chaplygin gas (GCG) model allows for an unified description of the recent accelerated expansion of the Universe and the evolution of energy density perturbations. This dark energy -dark matter unification is achieved through an exotic background fluid whose equation of state is given by p = −A/ρ α , where A is a positive constant and 0 < α ≤ 1. Stringent constraints on the model parameters can be obtained from recent WMAP and BOOMERanG bounds on the locations of the first few peaks and troughs of the Cosmic Microwave Background Radiation (CMBR) power spectrum as well as SNe Ia data. * Essay selected for an honorable mention by the Gravity Research Foundation, 2003.

2013

This article motivated by the recent articles and results of two authors. Recently, J. Sadeghi and H. Farahani presented a work [1], where they include viscosity and analyze general model, by this way they extended models considered by M. Khurshudyan [2] and . In this article, We tempt to consider varying Modified Chaplygin gas model in case of variable G and Λ. It is well known, that varying G and Λ gives rise to modified field equations and modified conservation laws. We will consider two different toy models. First model is a Universe with one component phenomenological gas of our consideration, while for the second model we assume existence of a composed fluid of gas and a matter with P = ω(t)ρm. Sign changeable interaction between fluids is accepted. We will analyze important cosmological parameters like EoS parameter of a fluid, deceleration parameter q of the model. *

Physical Review D, 2010

We study a generalized version of Chaplygin gas as unified model of dark matter and dark energy. Using realistic theoretical models and the currently available observational data from the age of the universe, the expansion history based on the type Ia supernovae, the matter power spectrum, the cosmic microwave background radiation anisotropy power spectra, and the perturbation growth factor we put the unified model under observational test. As the model has only two free parameters in the flat Friedmann background [ΛCDM (cold dark matter) model has only one free parameter] we show that the model is already tightly constrained by currently available observations. The only parameter space extremely close to the ΛCDM model is allowed in this unified model.

Journal of Cosmology and Astroparticle Physics, 2008

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 α > 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 α < 10 −5 , which makes the generalized Chaplygin gas practically indistinguishable from ΛCDM. 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 α. However, the growth of inhomogeneities seems to be particularly favoured either for sufficiently small values of α or for α 3. Thus, it appears that the viability of the generalized Chaplygin gas as a cosmological model is stronger

Eas Publications Series, 2009

We model the cosmic medium as the mixture of a generalized Chaplygin gas and a pressureless matter component. Within a neo-Newtonian approach we compute the matter power spectrum. The 2dFGRS data are used to discriminate between unified models of the dark sector and different models, for which there is separate dark matter, in addition to that accounted for by the generalized Chaplygin gas. Leaving the corresponding density parameters free, we find that the unified models are strongly disfavored. On the other hand, using unified model priors, the observational data are also well described, in particular for small and large values of the generalized Chaplygin gas

Physics Letters B, 2002

We extend the world model of Kamenshchik et al. to large perturbations by formulating a Zeldovich-like approximation. We sketch how this model unifies dark matter with dark energy in a geometric setting reminiscent of M-theory.  2002 Elsevier Science B.V. All rights reserved. PACS: 95.35.+d; 98.80.Hw; 04.50.+h After nearly two decades of reign [1], the Einsteinde Sitter dust model has been swept aside by observations of high redshift supernovae [2] which suggest that the Hubble expansion is accelerating. When combined with the Boomerang/Maxima data showing that the location of the first acoustic peak in the power spectrum of the microwave background is consistent with the inflationary prediction Ω = 1, the evidence for a net equation of state of the cosmic fluid lying in the range −1 w = P /ρ < −1/3 is compelling. Parametrically, w = P DE /(ρ DE + ρ DM ) = −Ω Λ gives a ratio of unclustered dark energy to clustered dark matter of order 7 : 3, thereby also resolving the longstanding Ω DM < 1 puzzle implied by peculiar velocity fields. The theoretical implications of these

We study the correspondence between field theoretic and holographic dark energy density of the universe with the modified Chaplygin gas (MCG) respectively both in a flat and non-flat FRW universe. We present an equivalent representation of the MCG with a homogeneous minimally coupled scalar field by constructing the corresponding potential. A new scalar field potential is obtained here which is physically realistic and important for cosmological model building. In addition we also present holographic dark energy model described by the MCG. The dynamics of the corresponding holographic dark energy field is determined by reconstructing the potential in a non-flat universe. The stability of the holographic dark energy in this case in a non-flat universe is also discussed.