Coupled dark energy with perturbed Hubble expansion rate

The coupling between dark sectors provides a possible approach to mitigate the coincidence problem of cosmological standard model. In this paper, dark energy is treated as a fluid with a constant equation of state, whose coupling with dark matter is proportional the Hubble parameter and energy density of dark energy, that is, $\bar{Q}=3\xi_x\bar{H}\bar{\rho}_x$. Particularly, we consider the Hubble expansion rate to be perturbed in the perturbation evolutions of dark sectors. Using jointing data sets which include cosmic microwave background radiation, baryon acoustic oscillation, type Ia supernovae, and redshift-space distortions, we perform a full Monte Carlo Markov Chain likelihood analysis for the coupled model. The results show that the mean value with errors of interaction rate is: $\xi_x=0.00305_{-0.00305-0.00305-0.00305}^{+0.000645+0.00511+0.00854}$ for $Q^{\mu}_A\parallel u^{\mu}_c$; $\xi_x=0.00317_{-0.00317-0.00317-0.00317}^{+0.000628+0.00547+0.00929}$ for $Q^{\mu}_A\parallel u^{\mu}_x$, which means that the recently cosmic observations favored small interaction rate which is up to the order of $10^{-3}$. Moreover, in contrast to the coupled model with unperturbed expansion rate, we find perturbed Hubble expansion rate could bring about negligible impact on the model parameter space.Comment: 11 pages, 5 figures; accepted for publication in Phys. Rev. D. arXiv admin note: substantial text overlap with arXiv:1401.5177, arXiv:1401.128

Cosmological constraints on interacting dark energy with redshift-space distortion after Planck data

The interacting dark energy model could propose a effective way to avoid the coincidence problem. In this paper, dark energy is taken as a fluid with a constant equation of state parameter $w_x$. In a general gauge, we could obtain two sets of different perturbation equations when the momentum transfer potential is vanished in the rest frame of dark matter or dark energy. There are many kinds of interacting forms from the phenomenological considerations, here, we choose $Q=3H\xi_x\rho_x$ which owns the stable perturbations in most cases. Then, according to the Markov Chain Monte Carlo method, we constrain the model by currently available cosmic observations which include cosmic microwave background radiation, baryon acoustic oscillation, type Ia supernovae, and $f\sigma_8(z)$ data points from redshift-space distortion. Jointing the geometry tests with the large scale structure information, the results show a tighter constraint on the interacting model than the case without $f\sigma_8(z)$ data. We find the interaction rate in 3$\sigma$ regions: $\xi_x=0.00372_{-0.00372- 0.00372-0.00372}^{+0.000768+0.00655+0.0102}$. It means that the recently cosmic observations favor a small interaction rate between the dark sectors, at the same time, the measurement of redshift-space distortion could rule out a large interaction rate in the 1$\sigma$ region.Comment: 18 pages, 10 figure

Unified dark fluid with fast transition: including entropic perturbations

In this paper, we investigate a unified dark fluid model with fast transition and entropic perturbations. An effective sound speed is designated as an additional free model parameter when the entropic perturbations are included, and if the entropic perturbations are zero, the effective sound speed will decrease to the adiabatic sound speed. In order to analyze the viability of the unified model, we calculate the squared Jeans wave number with the entropic perturbations. Furthermore, by using the Markov Chain Monte Carlo method, we perform a global fitting for the unified dark fluid model from the type Ia supernova Union 2.1, baryon acoustic oscillation and the full information of cosmic microwave background measurement given by the WMAP 7-yr data points. The constrained results favor a small effective sound speed. Compared to the $\Lambda$CDM, it is found that the cosmic observations do not favor the phenomenon of fast transition for the unified dark fluid model.Comment: 15 pages, 12 figure

Testing coupled dark energy with large scale structure observation

The coupling between the dark components provides a new approach to mitigate the coincidence problem of cosmological standard model. In this paper, dark energy is treated as a fluid with a constant equation of state, whose coupling with dark matter is $\bar{Q}=3H\xi_x\bar{\rho}_x$. In the frame of dark energy, we derive the evolution equations for the density and velocity perturbations. According to the Markov Chain Monte Carlo method, we constrain the model by currently available cosmic observations which include cosmic microwave background radiation, baryon acoustic oscillation, type Ia supernovae, and $f\sigma_8(z)$ data points from redshift-space distortion. The results show the interaction rate in 3$\sigma$ regions: $\xi_x=0.00328_{-0.00328-0.00328-0.00328}^{+0.000736+0.00549+0.00816}$, which means that the recently cosmic observations favor a small interaction rate which is up to the order of $10^{-2}$, meanwhile, the measurement of redshift-space distortion could rule out the large interaction rate in the 1$\sigma$ region.Comment: 12 pages, 10 figures. arXiv admin note: text overlap with arXiv:1401.128

Dynamics of nonlinear interacting dark energy models

We investigate the cosmological dynamics of interacting dark energy models in which the interaction function is a nonlinear in terms of the energy densities. Considering explicitly the interaction between a pressureless dark matter and a scalar field, minimally coupled to Einstein gravity, we explore the dynamics of the spatially flat FLRW universe for the exponential potential of the scalar field.. We perform the stability analysis for the three nonlinear interaction models of our consideration through the analysis of critical points and we investigate the cosmological parameters and we discuss the physical behaviour at the critical points. From the analysis of the critical points we find a number of possibilities that include the stable late time accelerated solution, $w$CDM-like solution, radiation-like solution and moreover the unstable inflationary solution as well.Comment: 15 pages, 10 figure

Reconciling the Tension Between Planck and BICEP2 Through Early Dark Energy

We show the possibility that the observational results of the primordial gravitational waves from Planck and BICEP2 for the tensor-to-scalar ratio $r$ can be reconciled when an early dark energy was included. This early dark energy behaves like a radiation component at very early epoch. This is equivalent to induce additional number of effective neutrino species: $\Delta N_{eff}=[\frac{7}{8}(\frac{4}{11})^{4/3}]^{-1}\rho_{de}(a)/\rho_{\gamma}(a)$, where $\rho_{\gamma}(a)$ is the photon energy density and the numerical factors arise from converting to effective neutrino species. And $\rho_{de}(a)$ is the energy density of early dark energy. Combining the Planck temperature data, the WMAP9 polarization data, and the baryon acoustic oscillation data with and without BICEP2 data, we find that in this early dark energy model the tension between the observations from Planck and BICEP2 was relived at $2\sigma$ regions. But it cannot be removed completely due to the small ratio of early dark energy constrained by the other cosmic observations. As a byproduct, the tension between observed values of Hubble parameter from Planck and the direct measurement of the Hubble constant was removed in this early dark energy model.Comment: 4 pages, 2 figures, typos corrected, references update

Latest astronomical constraints on some nonlinear parametric dark energy models

We consider nonlinear redshift-dependent equation of state parameters as dark energy models in a spatially flat Friedmann-Lema\^itre-Robertson-Walker universe. To depict the expansion history of the universe in such cosmological scenarios, we take into account the large scale behaviour of such parametric models and fit them using a set of latest observational data with distinct origin that includes cosmic microwave background radiation, Supernove Type Ia, baryon acoustic oscillations, redshift space distortion, weak gravitational lensing, Hubble parameter measurements from cosmic chronometers and finally the local Hubble constant from Hubble space telescope. The fitting technique avails the publicly available code Cosmological Monte Carlo (CosmoMC), to extract the cosmological information out of these parametric dark energy models. From our analysis it follows that those models could describe the late time accelerating phase of the universe, while they are distinguished from the $\Lambda-$cosmology.Comment: 11 pages, 12 figures, 4 tables, Published version in MNRA

Reheating in quintessential inflation via gravitational production of heavy massive particles: A detailed analysis

An improved version of the well-known Peebles-Vilenkin model unifying early inflationary era to current cosmic acceleration, is introduced in order to match with the theoretical values of the spectral quantities provided by it with the recent observational data about the early universe. Since the model presents a sudden phase transition, we consider the simplest way to reheat the universe - via the gravitational production of heavy massive particles - which assuming that inflation starts at GUT scales $\sim 10^{16}$ GeV, allows us to use the Wentzel-Kramers-Brillouin (WKB) approximation and consequently this enables us to perform all the calculations in an analytic way. Our results show that the model leads to a maximum temperature at the TeV regime, and passes the bounds to ensure the success of the Big Bang Nucleosynthesis. Finally, we have constrained the quintessence piece of the proposed improved version of the Peebles-Vilenkin model using various astronomical datasets available at present.Comment: 35 pages, 6 figures. Version accepted for publication in JCA

Cosmological constraints on an exponential interaction in the dark sector

Cosmological models where dark matter (DM) and dark energy (DE) interact with each other are the general scenarios in compared to the non-interacting models. The interaction is usually motivated from the phenomenological ground and thus there is no such rule to prefer a particular interaction between DM and DE. Being motivated, in this work, allowing an exponential interaction between DM and DE in a spatially flat homogeneous and isotropic universe, we explore the dynamics of the universe through the constraints of the free parameters where the strength of the interaction is characterized by the dimensionless coupling parameter $\xi$ and the equation of state (EoS) for DE, $w_x$, is supposed to be a constant. The interaction scenario is fitted using the latest available observational data. Our analyses report that the observational data permit a non-zero value of $\xi$ but it is very small and consistent with $\xi =0$. From the constraints on $w_x$, we find that both phantom ($w_x< -1$) and quintessence ($w_x> -1$) regimes are equally allowed but $w_x$ is very close to `$-1$'. The overall results indicate that at the background level, the interaction model cannot be distinguished from the base $\Lambda$-cold dark matter model while from the perturbative analyses, the interaction model mildly deviates from the base model. We highlight that, even if we allow DM and DE to interact in an exponential manner, but according to the observational data, the evidence for a non-zero coupling is very small.Comment: 13 pages, 7 figures, 2 tables; version published in MNRA

Constraining a dark matter and dark energy interaction scenario with a dynamical equation of state

In this work we have used the recent cosmic chronometers data along with the latest estimation of the local Hubble parameter value, $H_0$ at 2.4\% precision as well as the standard dark energy probes, such as the Supernovae Type Ia, baryon acoustic oscillation distance measurements, and cosmic microwave background measurements (PlanckTT $+$ lowP) to constrain a dark energy model where the dark energy is allowed to interact with the dark matter. A general equation of state of dark energy parametrized by a dimensionless parameter `$\beta$' is utilized. From our analysis, we find that the interaction is compatible with zero within the 1$\sigma$ confidence limit. We also show that the same evolution history can be reproduced by a small pressure of the dark matter.Comment: Accepted for publication in Physical Review