arXiv subjects

Weiqiang Yang

Publications and source records attributed to Weiqiang Yang.

At least 91 records · Page 5Linked to original sources

arXiv2018

Effects of Anisotropic Stress in Interacting Dark Matter - Dark Energy Scenarios

We study a novel interacting dark energy $-$ dark matter scenario where the anisotropic stress of the large scale inhomogeneities is considered. The dark energy has a constant equation of state and the interaction model produces stable perturbations. The resulting picture is constrained using different astronomical data aiming to measure the impact of the anisotropic stress on the cosmological parameters. Our analyses show that a non-zero interaction in the dark sector is allowed while a non-interaction scenario is recovered within 68\% CL. The anisotropic stress is also constrained to be small, and its zero value is permitted within 68\% CL. The dark energy equation of state, $w_x$, is also found to be close to `$-1$' boundary. However, from the ratio of the CMB TT spectra, we see that the model has a mild deviation from the $Λ$CDM cosmology while such deviation is almost forbidden from the CMB TT spectra alone. Although the deviation is not much significant, but from the present data, we cannot exclude such deviation. Overall, at the background level, the model is close to the $Λ$CDM cosmology while at the level of perturbations, a non-zero but a very small interaction in the dark sector is permitted. Perhaps, a more accurate conclusion can be made with the next generation of surveys. We also found that the region $w_x < -1$, is found to be effective to release the tension on $H_0$. Finally, from the Bayesian analysis, we find that $Λ$CDM remains in still preferred over the interacting scenarios.

astro-ph.CO↗

arXiv2018

Observational constraints on dynamical dark energy with pivoting redshift

We investigate the generalized Chevallier-Polarski-Linder (CPL) parametrization, which contains the pivoting redshift $z_p$ as an extra free parameter. We use various data combinations from cosmic microwave background (CMB), baryon acoustic oscillations (BAO), redshift space distortion (RSD), weak lensing (WL), joint light curve analysis (JLA), cosmic chronometers (CC), and we include a Gaussian prior on the Hubble constant value, in order to extract the observational constraints on various quantities. For the case of free $z_p$ we find that for all data combinations it always remains unconstrained, and there is a degeneracy with the current value of the dark energy equation of state $w_0$. For the case where $z_p$ is fixed to specific values, and for the full data combination, we find that with increasing $z_p$ the mean value of $w_0$ slowly moves into the phantom regime, however the cosmological constant is always allowed within 1$σ$ confidence-level. However, the significant effect is that with increasing $z_p$ the correlations between $w_0$ and $w_a$ change from negative to positive, with the case $z_p =0.35$ corresponding to no correlation. This feature indeed justifies why a non-zero pivoting redshift should be taken into account.

astro-ph.CO↗

arXiv2018

Observational Constraints on Oscillating Dark-Energy Parametrizations

We perform a detailed confrontation of various oscillating dark-energy parame-trizations with the latest sets of observational data. In particular, we use data from Joint Light Curve analysis (JLA) sample from Supernoave Type Ia, Baryon Acoustic Oscillations (BAO) distance measurements, Cosmic Microwave Background (CMB) observations, redshift space distortion, weak gravitational lensing, Hubble parameter measurements from cosmic chronometers, and we impose constraints on four oscillating models. From the analyses we find that the best-fit characters of almost all models are bent towards the phantom region, nevertheless in all of them the quintessential regime is also allowed within 1$σ$ confidence-level. Furthermore, the deviations from $Λ$CDM cosmology are not significant, however for two of the models they could be visible at large scales, through the impact on the temperature anisotropy of the CMB spectra and on the matter power spectra. Finally, we peform the Bayesian analysis, which shows that the current observational data support the $Λ$CDM paradigm over this set of oscillating dark-energy parametrizations.

astro-ph.CO↗

arXiv2018

Tale of stable interacting dark energy, observational signatures, and the $H_0$ tension

We investigate the observational consequences of a novel class of stable interacting dark energy (IDE) models, featuring interactions between dark matter (DM) and dark energy (DE). In the first part of our work, we start by considering two IDE models which are known to present early-time linear perturbation instabilities. Applying a transformation depending on the dark energy equation of state (EoS) to the DM-DE coupling, we then obtain two novel stable IDE models. Subsequently, we derive robust and accurate constraints on the parameters of these models, assuming a constant EoS $w_x$ for the DE fluid, in light of some of the most recent publicly available cosmological data. These include Cosmic Microwave Background (CMB) temperature and polarization anisotropy measurements from the \textit{Planck} satellite, a selection of Baryon Acoustic Oscillation measurements, Supernovae Type-Ia luminosity distance measurements from the JLA sample, and measurements of the Hubble parameter up to redshift $2$ from cosmic chronometers. Our analysis displays a mild preference for the DE fluid residing in the phantom region ($w_x<-1$), with significance up to 95\% confidence level, while we obtain new upper limits on the coupling parameter between the dark components. The preference for a phantom DE suggests a coupling function $Q<0$, thus a scenario where energy flows from the DE to the DM. We also examine the possibility of addressing the $H_0$ and $σ_8$ tensions, finding that only the former can be partially alleviated. Finally, we perform a Bayesian model comparison analysis to quantify the possible preference for the two IDE models against the standard concordance $Λ$CDM model, finding that the latter is always preferred with the strength of the evidence ranging from positive to very strong.

astro-ph.CO↗

arXiv2018

Large-scale (in-) stability Analysis of an Exactly Solved Coupled Dark-Energy Model

Assuming a non-gravitational interaction amongst the dark fluids of our universe namely, the dark matter and dark energy, we study a specific interaction model in the background of a spatially flat Friedmann-Lemaître-Robertson-Walker geometry. The interaction model, as we found, solves the background evolution in an analytic way when the dark energy takes a constant barotropic equation of state, $w_x$. In particular, we analyze two separate interaction scenarios, namely, when the dark energy is a fluid other than the vacuum energy (i.e., $w_x \neq -1$) and when it is vacuum energy itself (i.e., $w_x = -1$). We found that the interacting model with $w_x \neq -1$ produces stable perturbation at large scales for $w_x < -1$ with the coupling strength $ξ<0$. Both the scenarios have been constrained with the latest astronomical data having distinct origin. The analyses show that a very small interaction with coupling strength is allowed and within 68.3\% confidence-region, $ξ=0$ is recovered. The analyses further show that a large coupling strength significantly affects the large scale dynamics of the universe while according to the observational data the interaction models are very well consistent with the $Λ$-cosmology. Furthermore, we observe that for the vacuum interaction scenario, the tension on $H_0$ is not released while for the interacting dark energy scenario with $w_x < -1$, the tension on $H_0$ seems to be released partially because of the high error bars in $H_0$. Finally, we close the work with the Bayesian evidence which shows that the $Λ$CDM cosmology is favored over the two interacting scenarios.

gr-qc↗

arXiv2018

Large-scale Stability and Astronomical Constraints for Coupled Dark-Energy Models

We study large-scale inhomogeneous perturbations and instabilities of interacting dark energy (IDE) models. Past analysis of large-scale perturbative instabilities, has shown that we can only test IDE models with observational data when its parameter ranges are either $w_{x}\geq -1$ and $ξ\geq 0,$ or $w_{x}\leq -1~$ and $~ξ\leq 0$, where $w_{x}$ is the dark energy equation of state (EoS), and $ξ$ is a coupling parameter governing the strength and direction of the energy transfer. We show that by adding a factor $(1+w_{x})$ to the background energy transfer, the whole parameter space can be tested against all the data and thus, the instabilities in such interaction models can be removed. We test three classes of interaction model using the latest astronomical data from different sources. Precise constraints are found. Our analysis shows that a very small but non-zero deviation from pure $Λ$-cosmology is suggested by the observational data while the no-interaction scenario can be recovered at the 68.3% confidence-level. In particular, for three IDE models, identified as IDE 1, IDE 2, and IDE 3, the 68.3% CL constraints on the interaction coupling strengths are, $ξ= 0.0360_{-0.0360}^{+0.0091}$ (IDE 1), $ξ= 0.0433_{-0.0433}^{+0.0062}$ (IDE 2), $ξ= 0.1064_{-0.1064}^{+0.0437}$ (IDE 3). In addition, we find that the dark energy EoS tends towards the phantom region taking the 68.3% CL constraints, $w_x= -1.0230_{-0.0257}^{+0.0329}$ (IDE 1), $w_x= -1.0247_{-0.0302}^{+0.0289}$ (IDE 2), and $w_x= -1.0275_{-0.0318}^{+0.0228}$ (IDE 3). However, the possibility of $w_{x}>-1$ is also not rejected by the astronomical data used here. Moreover, we find in all IDE models that, as the value of Hubble constant decreases, the behavior of the dark energy EoS shifts from phantom to quintessence type with its EoS very close to that a simple cosmological constant at the present time.

astro-ph.CO↗

arXiv2018

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-Lemaître-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 $Λ-$cosmology.

gr-qc↗

arXiv2018

Late-time acceleration with steep exponential potentials

In this letter, we study the cosmological dynamics of steeper potential than exponential. Our analysis shows that a simple extension of an exponential potential allows to capture late-time cosmic acceleration and retain the tracker behavior. We also perform statefinder and $Om$ diagnostics to distinguish dark energy models among themselves and with $Λ$CDM. In addition, to put the observational constraints on the model parameters, we modify the publicly available CosmoMC code and use an integrated data base of baryon acoustic oscillation, latest Type Ia supernova from Joint Light Curves sample and the local Hubble constant value measured by the Hubble Space Telescope.

gr-qc↗

arXiv2017

Novel approach towards the large-scale stable Interacting Dark-Energy models and their Astronomical Bounds

Stability analysis of interacting dark energy models generally divides its parameters space into two regions: (i) $w_x \geq -1$ and $ξ\geq 0$ and (ii) $w_x \leq -1$ and $ξ\leq 0$, where $w_x$ is the dark energy equation of state and $ξ$ is the coupling strength of the interaction. Due to this separation, crucial information about the cosmology and phenomenology of these models may be lost. In a recent study it has been shown that one can unify the two regions with a coupling function which depends on the dark energy equation of state. In this work we introduce a new coupling function which also unifies the two regions of the parameter space and generalises the previous proposal. We analyse this scenario considering the equation of state of DE to be either constant or dynamical. We study the cosmology of such models and constrain both scenarios with the use of latest astronomical data from both background evolution as well as large scale structures. Our analysis shows that a non-zero value of the coupling parameter $ξ$ as well as the dark energy equation of state other than `$-1$' are allowed. However, within $1σ$ confidence level, $ξ= 0$, and the dark energy equation of state equal to `$-1$' are compatible with the current data. In other words, the observational data allow a very small but nonzero deviation from the $Λ$-cosmology, however, within $1σ$ confidence-region the interacting models can mimick the $Λ$-cosmology. In fact we observe that the models both at background and perturbative levels are very hard to distinguish form each other and from $Λ$-cosmology as well. Finally, we offer a rigorous analysis on the current tension on $H_0$ allowing different regions of the dark energy equation of state which shows that interacting dark energy models reasonably solve the current tension on $H_0$.

astro-ph.CO↗

arXiv2017

Effects of neutrino mass hierarchies on dynamical dark energy models

We investigate how three different possibilities of neutrino mass hierarchies, namely normal, inverted, and degenerate, can affect the observational constraints on three well known dynamical dark energy models, namely the Chevallier-Polarski-Linder, logarithmic, and the Jassal-Bagla-Padmanabhan parametrizations. In order to impose the observational constraints on the models, we performed a robust analysis using Planck 2015 temperature and polarization data, Supernovae type Ia from Joint Light curve analysis, baryon acoustic oscillations distance measurements, redshift space distortion characterized by $f(z)σ_8(z)$ data, weak gravitational lensing data from Canada-France-Hawaii Telescope Lensing Survey, and cosmic chronometers data plus the local value of the Hubble parameter. We find that different neutrino mass hierarchies return similar fit on almost all model parameters and mildly change the dynamical dark energy properties.

astro-ph.CO↗

arXiv2017

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 `$β$' is utilized. From our analysis, we find that the interaction is compatible with zero within the 1$σ$ confidence limit. We also show that the same evolution history can be reproduced by a small pressure of the dark matter.

astro-ph.CO↗

arXiv2016

Cosmic constraint on massive neutrinos in viable f(R) gravity with producing LCDM background expansion

Tensions between several cosmic observations were found recently, such as the inconsistent values of $H_{0}$ (or $σ_{8}$) were indicated by the different cosmic observations. Introducing the massive neutrinos in $Λ$CDM could potentially solve the tensions. Viable $f(R)$ gravity producing $Λ$CDM background expansion with massive neutrinos is investigated in this paper. We fit the current observational data: Planck-2015 CMB, RSD, BAO and SNIa to constrain the mass of neutrinos in viable $f(R)$ theory. The constraint results at 95\% confidence level are: $Σm_ν<0.202$ eV for the active neutrino case, $m_{ν, sterile}^{eff}<0.757$ eV with $N_{eff}<3.22$ for the sterile neutrino case. For the effects by the mass of neutrinos, the constraint results on model parameter at 95\% confidence level become $f_{R0}\times 10^{-6}> -1.89$ and $f_{R0}\times 10^{-6}> -2.02$ for two cases, respectively. It is also shown that the fitting values of several parameters much depend on the neutrino properties, such as the cold dark matter density, the cosmological quantities at matter-radiation equality, the neutrino density and the fraction of baryonic mass in helium. At last, the constraint result shows that the tension between direct and CMB measurements of $H_0$ gets slightly weaker in the viable $f(R)$ model than that in the base $Λ$CDM model.

astro-ph.CO↗

arXiv2016

Cosmological constraints on coupled dark energy

The coupled dark energy model provides a possible approach to mitigate the coincidence problem of cosmological standard model. Here, the coupling term is assumed as $\bar{Q}=3Hξ_x\barρ_x$, which is related to the interaction rate and energy density of dark energy. We derive the background and perturbation evolution equations for several coupled models. Then, we test these models by currently available cosmic observations which include cosmic microwave background radiation from Planck 2015, baryon acoustic oscillation, type Ia supernovae, $fσ_8(z)$ data points from redshift-space distortions, and weak gravitational lensing. The constraint results tell us there is no evidence of interaction at 2$σ$ level, it is very hard to distinguish different coupled models from other ones.

astro-ph.CO↗

arXiv2015

Constraints on the dark matter equation of state with redshift-space distortion

In this paper, we study a model which is composed by the cosmological constant and dark matter with nonzero equation of state parameter, which could be called as $Λ$wDM. In the synchronous gauge, we obtain the perturbation equations of dark matter, and deduce the evolution equations of growth factor about the dark matter and baryons. Based on the Markov Chain Monte Carlo method, we constrain this model by the recently available cosmic observations which include cosmic microwave background radiation, baryon acoustic oscillation, type Ia supernovae, and $fσ_8(z)$ data points from redshift-space distortion. The results present a tighter constraint on the model than the case without $fσ_8(z)$ data. In 3$σ$ regions, we find the dark matter equation of state parameter $w_{dm}$=$0.000111_{- 0.000701-0.00137-0.00180}^{+0.000688+0.00136+0.00181}$. After an extra model parameter $w_{dm}$ is considered, the difference between the minimum values of $χ^2$ of our model and standard model is $Δχ^2_{min}=0.598$. Although the currently available cosmic observations mildly favor the nonzero dark matter equation of state parameter, no significant deviation from the $Λ$CDM model is found in 1$σ$ region.

astro-ph.CO↗

arXiv2014

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, $\bar{Q}=3ξ_x\bar{H}\barρ_x$. 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: $ξ_x=0.00305_{-0.00305-0.00305-0.00305}^{+0.000645+0.00511+0.00854}$ for $Q^μ_A\parallel u^μ_c$; $ξ_x=0.00317_{-0.00317-0.00317-0.00317}^{+0.000628+0.00547+0.00929}$ for $Q^μ_A\parallel u^μ_x$, 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.

astro-ph.CO↗

arXiv2014

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 $\bar{Q}=3Hξ_x\barρ_x$. 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 $fσ_8(z)$ data points from redshift-space distortion. The results show the interaction rate in 3$σ$ regions: $ξ_x=0.00328_{-0.00328-0.00328-0.00328}^{+0.000736+0.00549+0.00816}$, 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$σ$ region.

astro-ph.CO↗

arXiv2014

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: $ΔN_{eff}=[\frac{7}{8}(\frac{4}{11})^{4/3}]^{-1}ρ_{de}(a)/ρ_γ(a)$, where $ρ_γ(a)$ is the photon energy density and the numerical factors arise from converting to effective neutrino species. And $ρ_{de}(a)$ 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 $2σ$ 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.

astro-ph.CO↗

arXiv2014

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 $Q=3Hξ_xρ_x$ 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 $fσ_8(z)$ 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 $fσ_8(z)$ data. We find the interaction rate in 3$σ$ regions: $ξ_x=0.00372_{-0.00372- 0.00372-0.00372}^{+0.000768+0.00655+0.0102}$. 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$σ$ region.

astro-ph.CO↗