arXiv subjects

Deng Wang

Publications and source records attributed to Deng Wang.

70 records · Page 4Linked to original sources

arXiv2017

Finslerian Universe May Reconcile Tensions between High and Low Redshift Probes

To reconcile the current tensions between high and low redshift observations, we perform the first constraints on the Finslerian cosmological models including the effective dark matter and dark energy components. We find that all the four Finslerian models could alleviate effectively the Hubble constant ($H_0$) tension and the amplitude of the root-mean-square density fluctuations ($σ_8$) tension between the Planck measurements and the local Universe observations at the 68$\%$ confidence level. The addition of a massless sterile neutrino and a varying total mass of active neutrinos to the base Finslerian two-parameter model, respectively, reduces the $H_0$ tension from $3.4σ$ to $1.9σ$ and alleviates the $σ_8$ tension better than the other three Finslerian models. Computing the Bayesian evidence, with respect to $Λ$CDM model, our analysis shows a weak preference for the base Finslerian model and moderate preferences for its three one-parameter extensions. Based on the model-independent Gaussian Processes, we propose a new linear relation which can describe the current redshift space distortions data very well. Using the most stringent constraints we can provide, we have also obtained the limits of typical model parameters for three one-parameter extensional models.

astro-ph.CO↗

arXiv2017

No evidence for dynamical dark energy in two models

To investigate whether the dark energy evolves over time, we propose two null tests and constrain them using the data combination of cosmic microwave background radiation, baryonic acoustic oscillations, Type Ia supernovae, Planck-2015 lensing and cosmic chronometers. We find that, for these two models, there is no evidence of the dynamical dark energy at the $1.2σ$ confidence level. Interestingly, both models could slightly alleviate (i) the current Hubble constant ($H_0$) tension between the global fitting derivation by the Planck collaboration and the local observation by Riess {\it et al.}; (ii) the root-mean-square density fluctuations ($σ_8$) tension between the Planck-2015 data and several low-redshift large scale structure probes.

astro-ph.CO↗

arXiv2017

Improved constraints on the dark energy equation of state using Gaussian processes

We perform a comprehensive study of the dark energy equation of state (EoS) utilizing the model-independent Gaussian processes (GP). Using a combination of the Union 2.1 data set, the 30 newly added H(z) cosmic chronometer data points and Planck's shift parameter, we modify the usual GaPP code and provide a tighter constraint on the dark energy EoS than the previous literature about GP reconstructions. Subsequently, we take the "controlling variable method" to investigate directly the effects of variable matter density parameter $Ω_{m0}$, variable cosmic curvature $Ω_{k0}$ and variable Hubble constant $H_0$ on the dark energy EoS, respectively. We find that too small or large $Ω_{m0}$, $Ω_{k0}$ and $H_0$ are all disfavored by our GP reconstructions based on current cosmological observations. Subsequently, we find that variable $Ω_{m0}$ and $Ω_{k0}$ affect the reconstructions of the dark energy EoS, but affect hardly the reconstructions of the normalized comoving distance $D(z)$ and its derivatives $D'(z)$ and $D"(z)$. However, variable $H_0$ affects the reconstructions of the dark energy EoS by affecting obviously those of $D(z), D'(z)$ and $D"(z)$. Furthermore, we find that the results of our reconstructions support substantially the recent local measurement of $H_0$ reported by Riess et al.

astro-ph.CO↗

arXiv2017

Cosmological forecasts from current observations of LIGO

We use the simulated gravitational-wave data to explore the evolution of the universe in light of current observations of the Laser Interferometer Gravitational-Wave Observatory (LIGO). Taking advantage of state-of-the-art Markov Chain Monte Carlo technique to constrain the basic cosmological parameters, the Hubble constant, present matter density parameter and equation of state of dark energy, we find that LIGO needs about, at least 5-year data accumulation, namely about 1000 events, to achieve the accuracy comparable to the Planck result. We also find that, from a new information channel, the constrained value of the Hubble constant from 1000 simulated events is more consistent with the direct local observation by Riess et al. than the indirect global measurement by the Planck Collaboration at the $2σ$ confidence level. The combination of gravitational waves and electromagnetic signals is very prospective to reveal the underlying physics of the universe.

astro-ph.CO↗

arXiv2017

Braneworld wormholes supported by astrophysical observations

In this study, we investigate the characteristics and properties of a traversable wormhole constrained by the current astrophysical observations in the framework of modified theories of gravity (MOG). As a concrete case, we study traversable wormhole space--time configurations in the Dvali--Gabadadze--Porrati (DGP) braneworld scenario, which are supported by the effects of the gravity leakage of extra dimensions. We find that the wormhole space--time structure will open in terms of the $2σ$ confidence level when we utilize the joint constraints supernovae (SNe) Ia + observational Hubble parameter data (OHD) + Planck + gravitational wave (GW) and $z<0.2874$. Furthermore, we obtain several model-independent conclusions, such as (i) the exotic matter threading the wormholes can be divided into four classes during the evolutionary processes of the universe based on various energy conditions; (ii) we can offer a strict restriction to the local wormhole space--time structure by using the current astrophysical observations; and (iii) we can clearly identify a physical gravitational resource for the wormholes supported by astrophysical observations, namely the dark energy components of the universe or equivalent space--time curvature effects from MOG. Moreover, we find that the strong energy condition is always violated at low redshifts.

gr-qc↗

arXiv2017

A new pressure-parametrization unified dark fluid model

We propose a new pressure-parametrization model to explain the accelerated expansion of the late-time Universe by considering the dark contents (dark matter and dark energy) as a unified dark fluid. To realize this model more physically, we reconstruct it with the quintessence and phantom scalar fields, respectively. We use the recent cosmological data to constrain this model, distinguish it from the standard cosmological model and find that the value of the Hubble constant $H_0=68.34^{+0.53}_{-0.92}$ supports the global measurement by the Planck satellite at the $1σ$ confidence level.

astro-ph.CO↗

arXiv2016

Determining $H_0$ with the latest HII galaxy measurements

We use the latest HII galaxy measurements to determine the value of $H_0$ adopting a combination of model-dependent and model-independent method. By constraining five cosmological models, we find that the obtained values of $H_0$ are more consistent with the recent local measurement by Riess et al. 2016 (hereafter R16) at $1σ$ confidence level, and that these five models prefer a higher best-fit value of $H_0$ than R16's result. To check the correctness of $H_0$ values obtained by model-dependent method, for the first time, we implement the model-independent Gaussian processes (GP) using the HII galaxy measurements. We find that the GP reconstructions also prefer a higher value of $H_0$ than R16's result. Therefore, we conclude that the current HII galaxy measurements support a higher cosmic expansion rate.

astro-ph.CO↗

arXiv2016

Wormholes from cosmological reconstruction based on Gaussian processes

We study the model-independent traversable wormholes from cosmological reconstruction based on Gaussian processes (GP). Using a combination of Union 2.1 SNe Ia data, the latest observational Hubble parameter data and recent Planck's shift parameter, we find that our GP method can give a tighter constraint on the normalized comoving distance, its derivatives and the dark energy equation of state than the previous work \cite{1}. Subsequently, two specific traversable wormhole solutions are obtained, i.e., the cases of a constant redshift function and a linear shape function. We find that, with decreasing cosmic acceleration, the traversal velocity $v$ of the former case increases and the amounts of exotic matter $I_V$ of the latter case decreases.

gr-qc↗

arXiv2016

Model-independent determination on $H_0$ using the latest $H(z)$ data

We perform the improved constraints on the Hubble constant $H_0$ by using the model-independent method, Gaussian Processes. Utilizing the latest 36 $H(z)$ measurements, we obtain $H_0=69.21\pm3.72$ km s$^{-1}$ Mpc$^{-1}$, which is consistent with the Planck 2015 and Riess et al. 2016 analysis at $1σ$ confidence level, and reduces the uncertainty from $6.5\%$ (Busti et al. 2014) to $5.4\%$. Different from the results of Busti et al. 2014 by only using 19 $H(z)$ measurements, our reconstruction results of $H(z)$ and the derived values of $H_0$ are independent of the choice of covariance functions.

gr-qc↗

arXiv2016

Reconstructing $f(R)$ gravity from viscous cosmology constrained by observations

In this paper, we reconstruct the $f(R)$ theory using the viscous $ω$CDM scenario (V-$ω$CDM) constrained by several differently astrophysical observations, including Type Ia supernovae (SNe Ia), observational Hubble parameter data (OHD), Wilkinson Microwave Anisotropy Probe 9-year data (WMAP-9), Planck observations and the single data point from the newest event GW150914 (GW). We find that the joint constraints from SNe Ia+OHD+Planck+GW data-sets give out a tighter restriction for the parameters of the V-$ω$CDM scenario than other constraints. Subsequently, we find that there exists a substantially high degeneracy among these reconstructed $f(R)$ theories in the past, and that they start exhibiting differently evolutional behaviors around the present epoch as well as much different in the distant future. Furthermore, we make a comparison between the reconstructed $f(R)$ theory with the V-$ω$CDM scenario and that with the $ω$CDM scenario constrained by using the SNe Ia+OHD+Planck+GW data-sets in the $f(R)-R$ plane, and find that the two scenarios share an extremely high degeneracy, which implies that the effect of bulk viscosity plays a negligible role in the V-$ω$CDM model during the whole evolutionary processes of the universe. In addition, one can also find that the reconstructed $f(R)$ theories using the two models just deviate from the standard Einstein gravity a little.

gr-qc↗

arXiv2016

Observational constraints and differential diagnosis for cosmic evolutionary models

In this paper, we have proposed a plotting method based on the " natural plotting rule " (NPR) which can be used to distinguish different cosmological scenarios more efficiently and obtain more useful information. By using the NPR, we have avoided the blindness to use different diagnostics when discovering that some scenarios can be hardly differentiated from each other, and develop a logical line to adopt different diagnostics. As a concrete instance, we take this method based on the NPR to distinguish several Cardassian scenarios from the base cosmology scenario, and one from the other. We place constraints on three Cardassian cosmological scenarios and their flat versions by utilizing the Type Ia supernovae (SNe Ia), baryonic acoustic oscillations (BAO), cosmic microwave background (CMB) radiation, observational Hubble parameter (OHD) data-sets as well as the single data point from the newest event GW150914, and discover that our results are more stringent than previous results for constraining the cosmological parameters of the Cardassian scenarios. We find that the flat original Cardassian (FOC) and original Cardassian (OC) scenarios can only be distinguished in the plane of $\{Ω_m,S_3^{(1)}\}$ at the present epoch, however, if applying the NPR to plot hierarchically for these Cardassian scenarios in the plane of $\{S_3^{(1)},S_4^{(1)}\}$, we can obtain more detailed information and distinguish the two scenarios better than before. More importantly, from the planes of $\{S_4,S_4^{(2)}\}$, $\{S_5^{(1)},S_5^{(2)}\}$, $\{S_3^{(2)},S_4^{(2)}\}$, $\{Ω_m,S_3^{(1)}\}$,$\{z,ω\}$ $\{ε(z),S_3^{(1)}\}$ and $\{z,Om\}$, we dsicover that the flat modified polytropic Cardassian (FMPC) scenario can be directly removed from the possible candidates of dark energy phenomenon, since its evolutional behavior deviates from the base cosmology scenario too much.

gr-qc↗

arXiv2016

Observational constraints and diagnostics for time-dependent dark energy models

In this paper, we constrain four time-dependent dark energy (TDDE) models by using the Type Ia supernovae (SNe Ia), baryonic acoustic oscillations (BAO), observational Hubble parameter (OHD) data-sets as well as the single data point from the newest event GW150914. Subsequently, adopting the best fitting values of the model parameters, we apply the original statefinder, statefinder hierarchy, the growth rate of matter perturbations and $Om(z)$ diagnostics to distinguish the TDDE scenarios and the $Λ$CDM scenario from each other. We discover that all the TDDE models and $Λ$CDM model can be distinguished better at the present epoch by using the statefinder hierarchy than using the original statefinder, the growth rate of matter perturbations and $Om(z)$ diagnostics, especially, in the planes of $\{S_3^{(1)},S_4^{(1)}\}$, $\{S_3^{(2)},S_4^{(2)}\}$, $\{S_5^{(1)},S_5^{(2)}\}$ and $\{S_4^{(2)},S_5^{(2)}\}$.

gr-qc↗

arXiv2016

Traversable holographic dark energy wormholes constrained by astronomical observations

In this letter, we investigate the traversable wormholes in the holographic dark energy (HDE) model constrained by the modern astronomical observations. First of all, we constrain the HDE model by adopting different data-sets, explore the cosmological background evolution of the HDE model, and find that the HDE model will be fitting better than the Ricci dark energy (RDE) model for the same SNe Ia data-sets by using the the so-called Akaike Information Criterions (AIC) and Bayesian Information Criterions (BIC) . Furthermore, we discover that if taking the SNe Ia data-sets, the wormholes will appear (open) when the redshift $z<0.027$. Subsequently, several specific traversable wormhole solutions are obtained, including the constant redshift function, traceless stress energy tensor, a special choice for the shape function as well as the case of isotropic pressure. Except for the first case, it is very necessary to theoretically construct the traversable wormholes by matching the exterior geometries to the interior geometries. Naturally, one can easily find that the dimensions of the wormholes for the left cases are substantially finite.

gr-qc↗

arXiv2016

Diagnostics and future evolution analysis of the two parametric models

In this paper, we apply three diagnostics including $Om$, Statefinder hierarchy and the growth rate of perturbations into discriminating the two parametric models for the effective pressure with the $Λ$CDM model. By using the $Om$ diagnostic, we find that both the model 1 and the model 2 can be hardly distinguished from each other as well as the $Λ$CDM model in terms of 68\% confidence level. As a supplement, by using the Statefinder hierarchy diagnostics and the growth rate of perturbations, we discover that not only can our two parametric models be well distinguished from $Λ$CDM model, but also, by comparing with $Om$ diagnostic, the model 1 and the model 2 can be distinguished better from each other. In addition, we also explore the fate of universe evolution of our two models by means of the rip analysis.

gr-qc↗

arXiv2016

Geometric dark energy traversable wormholes constrained by astrophysical observations

In this letter, we introduce the astrophysical observations into the wormhole research, which is not meant to general parameters constraints for the dark energy models, in order to understand more about in which stage of the universe evolutions wormholes may exist through the investigation of the evolution behavior of the cosmic equation of state parameter. As a concrete instance, we investigate the Ricci dark energy (RDE) traversable wormholes constrained by astrophysical data-sets. Particularly, we can discover from Fig. \ref{fig5} of the present work, when the effective equation of state parameter $ω_X<-1$, namely, the Null Energy conditions (NEC) is violated clearly, the wormholes will appear (open). Subsequently, six specific solutions of static and spherically symmetric traversable wormhole supported by the RDE are obtained. Except for the case of constant redshift function, in which the solution is not only asymptotically flat but also traversable, the remaining five solutions are all not asymptotically flat, therefore, the exotic matter from the RDE fluids is spatially distributed in the vicinity of the throat. Furthermore, we analyze the physical characteristics and properties of the RDE traversable wormholes. It is worth noting that, through the astrophysical observations, we get constraints on the parameters of RDE model, explore the type of exotic RDE fluids in different stages of the universe changing, limit the number of available models for wormhole research, reduce the number of the wormholes corresponding to different parameters for RDE model and provide a more apparent picture for wormhole investigations from the new perspective of observational cosmology background

gr-qc↗

arXiv2015

Modeling phantom energy wormholes from Shan-Chen fluids

In recent years, cosmic observational data have reported that our present universe is undergoing an accelerated expansion, which has been termed as mysterious "dark energy" phenomena, that is, the origin of dark energy has not been determined yet. According to our previous work that a new equation of state \cite{X.Shan and H.Chen1993} can be employed to explain the dark energy, and we are very interested in investigating the astrophysical scale properties of dark energy based on the new cosmological fluids given that the universe is filled with a dark energy fluid everywhere. Hence, in this paper, we study the exact solutions of spherically-symmetrical Einstein field equations describing wormholes supported by phantom energy from Shan-Chen (SC) fluids by considering an obvious relation between the transversal pressure and energy density which is different from our previous work \cite{111}. We have still investigated the important case $ψ\approx1$ which corresponds to the " saturation effect ", and this regime corresponds to an effective form of " asymptotic freedom ", occurring at cosmological rather than subnuclear scales. Then we find out two solutions by making some special choices for the shape function $b(r)$ and discuss the singularities of the solutions and find that the spacetimes are both geodesically incomplete. At the same time, it is worth noting that whether the solutions are geodesically complete or incomplete depends on the appropriate choice of the shape function $b(r)$ through our works. In addition, we match our interior solutions to the exterior Schwarzschild solutions and calculate out the total mass of the wormhole when $r\leq a$.

gr-qc↗