arXiv subjects

Deng Wang

Publications and source records attributed to Deng Wang.

At least 55 records · Page 3Linked to original sources

arXiv2021

First comprehensive constraints on the Finslerian models using cosmological observations

We perform the first comprehensive constraints on two Finslerian models, i.e., the simplest Finslerian $Λ$CDM (F$Λ$) and non-flat F$Λ$ models using the Type Ia supernovae, baryonic acoustic oscillations, cosmic microwave background and lensing observations. Using the most stringent constraints we can provide, we find that the constrained typical parameters of both Finslerian models are all consistent with zero at the $2σ$ confidence level (C.L.). This means that both Finslerian models just deviate very slightly from the $Λ$CDM one, which is also verified by using two geometrical diagnostics to distinguish three different models from each other. We also find that a spatially flat universe is still preferred in the framework of Finsler geometry, that our measured values of the spectral index $n_s$ of primordial power spectrum in both Fisnlerian models exclude the scale invariance at more than $8σ$ C.L., and that the current $H_0$ tension can be relieved from $3.4σ$ to $2.9σ$ and $2.8σ$ in the F$Λ$ and non-flat F$Λ$ models, respectively.

astro-ph.CO↗

arXiv2021

Constraining viscous dark energy models with the latest cosmological data

Based on the assumption that the dark energy possessing bulk viscosity is homogenously and isotropically permeated in the universe, we propose three new viscous dark energy (VDE) models to characterize the accelerating universe. By constraining these three models with the latest cosmological observations, we find that they just deviate very slightly from the standard cosmological model and can alleviate effectively the current $H_0$ tension between the local observation by the Hubble Space Telescope and the global measurement by the Planck Satellite. Interestingly, we conclude that a spatially flat universe in our VDE model with cosmic curvature is still supported by current data, and the scale invariant primordial power spectrum is strongly excluded at least at the $5.5σ$ confidence level in three VDE models as the Planck result. We also give the $95\%$ upper limits of the typical bulk viscosity parameter $η$ in three VDE scenarios.

astro-ph.CO↗

arXiv2021

Exploring New Physics Beyond the Standard Cosmology with Dark Energy Survey Year 1 Data

With the recent data from the first year of the Dark Energy Survey (DES Y1), we attempt to probe whether there is new physics beyond the standard cosmology and to reconcile the $σ_8$ tension between the DES Y1 and Planck datasets in three alternative cosmological models. Combining the galaxy clustering and weak gravitational lensing data from the DES Y1 with other cosmological observations including cosmic microwave background radiation, baryon acoustic oscillations, Type Ia supernovae (SNe Ia) and Planck lensing, we find that: (i) For the interacting dark energy model, we have an updated constraint on the modified matter expansion rate $ε=-0.00004\pm 0.00031$, which indicates that there is no hint of interaction between dark matter and dark energy in the dark sector of the universe; (ii) For the viscous dark energy model, up to now, the strictest constraint on the bulk viscosity coefficient $η<0.00152$ at the $2σ$ confidence level is obtained; (iii) For the dynamical dark energy model, our constraint on the typical parameter $β=-0.04\pm0.12$ implies that there is still no evidence of dynamical dark energy. Meanwhile, we find the $σ_8$ tension can be effectively alleviated in the above three alternatives by constraining them with the DES Y1 and Planck datasets separately.

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arXiv2020

Cosmography in $f(Q)$ gravity

Cosmography is an ideal tool to investigate the cosmic expansion history of the Universe in a model-independent way. The equations of motion in modified theories of gravity are usually very complicated; cosmography may select practical models without imposing arbitrary choices a priori. We use the model-independent way to derive $f(z)$ and its derivatives up to fourth order in terms of measurable cosmographic parameters. We then fit those functions into the luminosity distance directly. We perform the MCMC analysis by considering three different sets of cosmographic functions. Using the largest supernovae Ia Pantheon sample, we derive the constraints on the Hubble constant $H_0$ and the cosmographic functions, and find that the former two terms in Taylor expansion of luminosity distance work dominantly in $f(Q)$ gravity.

gr-qc↗

arXiv2020

Cosmology Intertwined III: $f σ_8$ and $S_8$

The standard $Λ$ Cold Dark Matter cosmological model provides a wonderful fit to current cosmological data, but a few tensions and anomalies became statistically significant with the latest data analyses. While these anomalies could be due to the presence of systematic errors in the experiments, they could also indicate the need for new physics beyond the standard model. In this Letter of Interest we focus on the tension of the Planck data with weak lensing measurements and redshift surveys, about the value of the matter energy density $Ω_m$, and the amplitude or rate of the growth of structure ($σ_8,fσ_8$). We list a few interesting models for solving this tension, and we discuss the importance of trying to fit with a single model a full array of data and not just one parameter at a time.

astro-ph.CO↗

arXiv2020

Cosmology Intertwined II: The Hubble Constant Tension

The current cosmological probes have provided a fantastic confirmation of the standard $Λ$ Cold Dark Matter cosmological model, that has been constrained with unprecedented accuracy. However, with the increase of the experimental sensitivity a few statistically significant tensions between different independent cosmological datasets emerged. While these tensions can be in portion the result of systematic errors, the persistence after several years of accurate analysis strongly hints at cracks in the standard cosmological scenario and the need for new physics. In this Letter of Interest we will focus on the $4.4σ$ tension between the Planck estimate of the Hubble constant $H_0$ and the SH0ES collaboration measurements. After showing the $H_0$ evaluations made from different teams using different methods and geometric calibrations, we will list a few interesting new physics models that could solve this tension and discuss how the next decade experiments will be crucial.

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arXiv2020

Cosmology Intertwined I: Perspectives for the Next Decade

The standard $Λ$ Cold Dark Matter cosmological model provides an amazing description of a wide range of astrophysical and astronomical data. However, there are a few big open questions, that make the standard model look like a first-order approximation to a more realistic scenario that still needs to be fully understood. In this Letter of Interest we will list a few important goals that need to be addressed in the next decade, also taking into account the current discordances present between the different cosmological probes, as the Hubble constant $H_0$ value, the $σ_8 - S_8$ tension, and the anomalies present in the Planck results. Finally, we will give an overview of upgraded experiments and next-generation space-missions and facilities on Earth, that will be of crucial importance to address all these questions.

astro-ph.CO↗

arXiv2020

Cosmology Intertwined IV: The Age of the Universe and its Curvature

A precise measurement of the curvature of the Universe is of primeval importance for cosmology since it could not only confirm the paradigm of primordial inflation but also help in discriminating between different early Universe scenarios. The recent observations, while broadly consistent with a spatially flat standard $Λ$ Cold Dark Matter ($Λ$CDM) model, are showing tensions that still allow (and, in some cases, even suggest) a few percent deviations from a flat universe. In particular, the Planck Cosmic Microwave Background power spectra, assuming the nominal likelihood, prefer a closed universe at more than 99\% confidence level. While new physics could be in action, this anomaly may be the result of an unresolved systematic error or just a statistical fluctuation. However, since a positive curvature allows a larger age of the Universe, an accurate determination of the age of the oldest objects provides a smoking gun in confirming or falsifying the current flat $Λ$CDM model.

astro-ph.CO↗

arXiv2020

Can $f(T)$ gravity resolve the $H_0$ tension?

Motivated by the discrepancy in measurements of $H_0$ between local and global probes, we investigate whether teleparallel gravities could be a better model to describe the present days observations or at least to alleviate the $H_0$ tension. Specifically, in this work we study and place constraints on three popular $f(T)$ models in light of the Planck-2018 CMB data release. We find that the $f(T)$ power-law model can alleviate the $H_0$ tension from $4.4σ$ to $1.9σ$ level, while the $f(T)$ model of two exponential fail to resolve this inconsistency. Moreover, for the first time, we obtain constraints on the effective number of relativistic species $N_{eff}$ and on the sum of the neutrino masses $Σm_ν$ in $f(T)$ gravity. We find that the constraints obtained are looser than in $Λ$CDM. However, the introduction of massive neutrinos into the cosmological model alleviate the $H_0$ tension for the power-law model. Finally, we find that whether a viable $f(T)$ theory can mitigate the $H_0$ tension depends on the mathematical structure of the distortion factor $y(z,\,b)$. These results could provide a clue for theoreticians to write a more physical-motivated expression of $f(T)$ function.

astro-ph.CO↗

arXiv2020

Thin-shell wormholes constrained by cosmological observations

We investigate the thin-shell wormholes constrained by cosmological observations for the first time in the literature. Without loss of generality, we study the thin-shell wormholes in $ω$CDM model and analyze their stability under perturbations preserving the symmetry. Firstly, we constrain the $ω$CDM model using a combination of Union 2.1 SNe Ia data, the latest $H(z)$ data and CMB data. Secondly, we use the constrained dark energy equation of state (EoS) $ω$ which lies in $[-1.05,-0.89]$ to investigate thin-shell wormholes of various black hole spacetimes. We find that the stable Schwarzschild and Reinssner-Nordström thin-shell wormholes constrained by cosmological observations do not exist. In addition, the method we developed can be applied into exploring the stable thin-shell wormholes from any black hole spacetime in the framework of any cosmological theory.

gr-qc↗

arXiv2020

Weak equivalence principle, swampland and $H_0$ tension with fast single radio bursts FRB 180924 and FRB 190523

Two new fast single radio bursts FRB 180924 and FRB 190523 well localized to massive galaxies have opened a new window to probe and characterize how cosmic baryons are allocated between galaxies, their surroundings and intergalactic medium. We are motivated by testing Einstein's weak equivalence principle with these two cosmic transients which have accurate redshifts. Using photons with different energies emitted by FRB 180924, we obtain, so far, the most stringent bound $Δγ<2.16\times10^{-10}$ for non-repeating FRBs with accurate redshifts when only considering the gravitational potential of the Milk Way. If using the gravitational potential of the Laniakea supercluster instead of the Milk Way one, we also obtain the strictest bound $Δγ<1.06\times10^{-14}$ to date. In light of rapid progress of FRB cosmology, towards the next two decades, we give an universal limitation $Δγ<8.24\times10^{-22}$ from photons with different energies emitted by single FRBs with accurate redshifts. Moreover, we analyze detailedly the effects of various astrophysical parameters on the precision of weak equivalence principle. We also estimate the abilities of single FRBs with known redshifts to test the validity of swampland criterion, and to distinguish which value of $H_0$ is preferred.

astro-ph.CO↗

arXiv2020

Multi-feature universe: large parameter space cosmology and the swampland

Under the belief that the universe should be multi-feature and informative, we employ a model-by-model comparison method to explore the possibly largest upper bound on the swampland constant $c$. Considering the interacting quintessence dark energy as the comparison model, we constrain the large parameter space interacting dark energy model, a 12-parameter extension to the $Λ$CDM cosmology, in light of current observations. We obtain the largest $2σ$ ($3σ$) bound so far, $c\lesssim1.62$ $(1.94)$, which would allow the existences of a number of string theory models of dark energy such as 11-dimensional supergravity with double-exponential potential, $O(16)\times O(16)$ heterotic string and some Type II string compactifications. For inflationary models with concave potential, we find the $2σ$ ($3σ$) bound $c\lesssim0.13$ $(0.14)$, which is still in strong tension with the string-based expectation $c \sim \mathcal{O}(1)$. However, combining Planck primordial non-Gaussianity with inflation constraints, it is interesting that the Dirac-Born-Infeld inflation with concave potential gives the $2σ$ ($3σ$) bound $c\lesssim0.53$ $(0.58)$, which is now in a modest tension with the swampland conjecture. Using the Bayesian evidence as the model selection tool, it is very surprising that our 18-parameter multi-feature cosmology is extremely strongly favored over the $Λ$CDM model.

astro-ph.CO↗

arXiv2019

Searching for the Evidence of Dynamical Dark Energy

In the statistical framework of model-independent Gaussian processes (GP), we search for the evidence of dynamical dark energy (DDE) using the "Joint Light-curve Analysis" (JLA) Type Ia supernovae (SNe Ia) sample, the 30 latest cosmic chronometer data points (H(z)), Planck's shift parameter from cosmic microwave background (CMB) anisotropies, the 156 latest HII galaxy measurements and 79 calibrated gamma-ray bursts (GRBs). We find that the joint constraint from JLA + H(z) + CMB + HII + GRB supports the global measurement of $H_0$ by Planck collaboration very much in the low redshift range $z\in[0, 0.76]$ at the $2σ$ confidence level (C.L.), gives a cosmological constant crossing (quintom-like) equation of state (EoS) of DE at the $2σ$ C.L. and implies that the evolution of the late-time Universe may be actually dominated by the DDE.

astro-ph.CO↗

arXiv2019

Cosmology with Type II Supernovae

With the recent progresses on the Type II supernovae, we attempt to investigate whether there does exist new physics beyond the standard cosmological paradigm, i.e., the cosmological constant $Λ$ plus cold dark matter ($Λ$CDM). Constraining four alternative cosmological models with a data combination of currently available Type II supernovae calibrated by the standard color method, Type Ia supernovae, baryon acoustic oscillations, cosmic microwave background and cosmic chronometers, at the $1σ$ confidence level, we find that: (i) a spatially flat universe is supported for the non-flat $Λ$CDM model; (ii) the constrained equation of state of dark energy $ω$ is consistent with the $Λ$CDM hypothesis for the $ω$CDM model where $ω$ is a free parameter; (iii) for the decaying vacuum model, there is no evidence of interaction between dark matter and dark energy in the dark sector of the universe; (iv) there is also no hint of dynamical dark energy for the dark energy density-parametrization scenario. It is very obvious that a larger Type II supernovae sample is required, if we expect to draw definitive conclusions about the formation and evolution of the universe.

astro-ph.CO↗

arXiv2018

Dark Energy Constraints in light of Pantheon SNe Ia, BAO, Cosmic Chronometers and CMB Polarization and Lensing Data

To explore whether there is new physics going beyond the standard cosmological model or not, we constrain seven cosmological models by combining the latest and largest Pantheon Type Ia supernovae sample with the data combination of baryonic acoustic oscillations, cosmic microwave background radiation, Planck lensing and cosmic chronometers. We find that a spatially flat universe is preferred in the framework of $Λ$CDM cosmology, that the constrained equation of state of dark energy is very consistent with the cosmological constant hypothesis, that there is no evidence of dynamical dark energy, that there is no hint of interaction between dark matter and dark energy in the dark sector of the universe, and that there does not exist the sterile neutrinos in the neutrino sector of the universe. We also give the 95$\%$ limit of the total mass of three active neutrinos $Σm_ν<0.178$ eV. It is clear that there is no any departure from the standard cosmological model based on current observational datasets.

astro-ph.CO↗

arXiv2018

Can decaying vacuum elucidate the late-time dynamics of the Universe ?

We examine the decay vacuum model with a parameter $ε$ that indicates the vacuum energy decay rate. By constraining this model with cosmic microwave background radiation, baryon acoustic oscillation, type Ia supernovae and 30 H(z) cosmic chronometer data points, we find that $ε=-0.0003\pm0.00024$ with the best fitted $χ^{2}$ value slightly smaller than that in the $Λ$CDM model. A negative value of $ε$ suggesting dark matter energy decay into vacuum energy. We also obtain the Hubble constant $H_{0}=68.05\pm0.56$ that can alleviate the current $H_{0}$ tension between the local observation by the Hubble Space Telescope and the global measurement by the Planck Satellite. Using the effective equation of state formalism, we find this model is quintessence-like.

astro-ph.CO↗

arXiv2017

Machine Learning Cosmic Expansion History

We use the machine learning techniques, for the first time, to study the background evolution of the universe in light of 30 cosmic chronometers. From 7 machine learning algorithms, using the principle of mean squared error minimization on testing set, we find that Bayesian ridge regression is the optimal method to extract the information from cosmic chronometers. By use of a power-law polynomial expansion, we obtain the first Hubble constant estimation $H_0=65.95^{+6.98}_{-6.36}$ km s$^{-1}$ Mpc$^{-1}$ from machine learning. From the view of machine learning, we may rule out a large number of cosmological models, the number of physical parameters of which containing $H_0$ is larger than 3. Very importantly and interestingly, we find that the parameter spaces of 3 specific cosmological models can all be clearly compressed by considering both their explanation and generalization abilities.

astro-ph.CO↗

arXiv2017

Exploring the expansion dynamics of the universe from galaxy cluster surveys

To understand the expansion dynamics of the universe from galaxy cluster scales, using the angular diameter distance (ADD) data from two different galaxy cluster surveys, we constrain four cosmological models to explore the underlying value of $H_0$ and employ the model-independent Gaussian Processes to investigate the evolution of the equation of state of dark energy. The ADD data in the X-ray bands consists of two samples covering the redshift ranges [0.023, 0.784] and [0.14, 0.89], respectively. We find that: (i) For these two samples, the obtained values of $H_0$ are more consistent with the recent local observation by Riess et al. than the global measurement by the Plank Collaboration, and the $Λ$CDM model is still preferred utilizing the information criterions; (ii) For the first sample, there is no evidence of dynamical dark energy (DDE) at the $2σ$ confidence level (CL); (iii) For the second one, the reconstructed equation of state of dark energy exhibits a phantom-crossing behavior in the relatively low redshift range over the $2σ$ CL, which gives a hint that the late-time universe may be actually dominated by the DDE from galaxy cluster scales; (iv) By adding a combination of Type Ia Supernovae, cosmic chronometers and Planck-2015 shift parameter and HII galaxy measurements into both ADD samples, the DDE exists evidently over the $2σ$ CL.

astro-ph.CO↗