Cosmological constraints on a decomposed Chaplygin gas

Abstract

Any unified dark matter cosmology can be decomposed into dark matter interacting with vacuum energy, without introducing any additional degrees of freedom. We present observational constraints on an interacting vacuum plus dark energy corresponding to a generalised Chaplygin gas cosmology. We consider two distinct models for the interaction leading to either a barotropic equation of state or dark matter that follows geodesics, corresponding to a rest-frame sound speed equal to the adiabatic sound speed or zero sound speed, respectively. For the barotropic model, the most stringent constraint on α comes from the combination of CMB+SNIa+LSS(m) gives α < 1.44 × 10 −5 at the 95% confidence level, which indicates that the barotropic model must be extremely close to the ΛCDM cosmology. For the case where the dark matter follows geodesics, perturbations have zero sound speed, and CMB+SNIa+gISW then gives the much weaker constraint −0.1522 < α < 0.2556 at the 95% confidence level.

Large-scale stable interacting dark energy model: Cosmological perturbations and observational constraints

“…Therefore, in this work, we only consider the "geodesic model". Note also that the decomposed GCG model [49] describes DM interacting with the vacuum energy (w = −1), and thus the perturbation of DE is always zero in the DM-comoving frame within the "geodesic model". In our work, we focus on the w = const case, for which one must seriously treat the DE perturbation, as there may exist the large-scale instability mentioned above.…”

“…So, this interacting DE model is equivalent to a decomposed NGCG model. Actually, a decomposed generalized Chaplygin gas (GCG) model has been discussed [49]. In Ref.…”

“…In Ref. [49], two covariant interaction models are investigated-(1) the so called "barotropic model" in which the covariant interaction form is proportional to the gradient of the local DM density and (2) the "geodesic model" where the energy-momentum transfer is parallel to the DM four-velocity. The "geodesic model" is widely studied in the literature; in this model there is no momentum transfer in the rest frame of DM.…”

Testing the Interacting Dark Energy Model with Cosmic Microwave Background Anisotropy and Observational Hubble Data

“…For the above unified dark fluid model, one also could decompose it into dark matter interacting with vacuum energy. This kind of decomposed model has been constrained in [27,28], with the joint constraint from the geometry measurement and growth rate, the decomposed model parameter α is constrained in the order of 10 −4 [28]. For the decomposed dark fluid model, the interaction between dark energy and dark matter might be naturally introduced without adding any additional degrees of freedom, this is a possibility of interaction between the dark sectors.…”

Observational constraints to a unified cosmological model

“…II A. There is a plethora of cosmological models based on the same idea [18]; they are build either based on theoretical motivations [19][20][21][22][23][24][25][26][27][28][29] or on phenomenological ones [30][31][32][33][34][35][36][37][38]. Our model is built on phenomenological grounds.…”