Generalizing the generalized Chaplygin gas

Abstract

The generalized Chaplygin gas is characterized by the equation of state p = −A/ρ α , with α > −1 and w > −1. We generalize this model to allow for the cases where α < −1 or w < −1. This generalization leads to three new versions of the generalized Chaplygin gas: an early phantom model in which w ≪ −1 at early times and asymptotically approaches w = −1 at late times, a late phantom model with w ≈ −1 at early times and w → −∞ at late times, and a transient model with w ≈ −1 at early times and w → 0 at late times. We consider these three cases as models for dark energy alone and examine constraints from type Ia supernovae and from the subhorizon growth of density perturbations. The transient Chaplygin gas model provides a possible mechanism to allow for a currently accelerating universe without a future horizon, while some of the early phantom models produce w < −1 without either past or future singularities.

Post-Planck dark energy constraints

“…This form is known as the Generalized Chaplygin Gas (GCG) equation of state. In a later work Scherrer and Sen [12] considered the parameter range α < 0 to describe diverse cosmological behaviors. Assuming a spatially homogeneous and isotropic universe along with the energy momentum conservation equation gives us…”

“…The second parametrization which we consider, was proposed by Bento, Bertolami and Sen [11] and subsequently was discussed [19][20][21][22] for more general parameter ranges by Scherrer and Sen [12] and is known as Generalized Chaplygin Gas (GCG) parametrization. In this parametrization, for a certain choice of parameter range, the dark energy equation of state behaves like a thawing class of scalar field models where the present acceleration is a transient one.…”

“…A variety of such scalar field models, including string theory embeddings for a positive Cosmological Constant [6], quintessence [7], k-essence [8], phantom fields [9], tachyons [10] etc have been proposed. Other than scalar field models, a barotropic fluid with an equation of state p(ρ), such as the Generalized Chaplygin Gas (GCG) and its various generalizations [11,12] have also been considered for dark energy model building.…”

A conventional approach to the dark-energy concept

“…Other physically-motivated models, predicting an accelerated expansion, have also appeared in the literature, involving holographic gravity (Cohen et al 1999;Li 2004;Pavón & Zimdahl 2005), Chaplygin gas (Kamenshchik et al 2001;Bean & Doré 2003;Sen & Scherrer 2005), Cardassian cosmology (Freese & Lewis 2002;Wang et al 2003), theories of compactified internal dimensions (Perivolaropoulos 2003), and massvarying neutrinos (Fardon et al 2004;Peccei 2005).…”

Dark Energy Constraints on Red-Shift-Based Gravity

“…The positive cosmological constant would be defined either geometrically as modifying the left hand side of Einstein equations or as a kinematic term on the right hand side with the equation of state parameter = −1; however, the fine tuning problem causes some difficulties [9][10][11][12][13][14][15][16]. There are various scalar field models of Dark Energy [16][17][18][19][20][21][22][23][24][25][26][27][28][29][30][31][32][33]. These models indeed are the outcomes of modifying the right hand side of the Einstein equations, = , by considering a source term with an equation of state parameter < −1/3 which is recognized as Dark Energy.…”