arXiv subjects

Weiqiang Yang

Publications and source records attributed to Weiqiang Yang.

At least 73 records · Page 4Linked to original sources

arXiv2020

Nonlinear interacting cosmological models after Planck 2018 legacy release and the $H_0$ tension

Interacting dark energy models are widely renowned for giving an explanation to the cosmic coincidence problem as well as several observational issues. According to the recent observational data, and so far we are concerned with the literature, the choice of the interaction function between dark matter and dark energy is always questionable since there is no such underlying theory that could derive it. Thus, in this work we have raised this issue by proposing two new nonlinear interaction functions and constrain them using cosmic microwave background (CMB) from Planck 2018, baryon acoustic oscillations (BAO), dark energy survey and a measurement of the Hubble constant $H_0$ from Hubble Space Telescope (HST) 2019. The dark energy equation of state is considered to be constant throughout the work and the geometry of the universe is assumed to be homogeneous and isotropic with zero spatial curvature. Our analyses report that a non-zero interaction is always allowed by the observational data and the dark energy equation of state is bent towards the phantom regime. In particular, when $H_0$ from HST is added to Planck 2018+BAO, we find an evidence for a non-zero coupling at more than $2σ$ confidence level. Our analyses also report that for both the models, $H_0$ is close to its local measurements and thus alleviating the $H_0$ tension. In particular, one of the interacting models perfectly solves the $H_0$ tension.

astro-ph.CO↗

arXiv2019

Dawn of the dark: unified dark sectors and the EDGES Cosmic Dawn 21-cm signal

While the origin and composition of dark matter and dark energy remains unknown, it is possible that they might represent two manifestations of a single entity, as occurring in unified dark sector models. On the other hand, advances in our understanding of the dark sector of the Universe might arise from Cosmic Dawn, the epoch when the first stars formed. In particular, the first detection of the global 21-cm absorption signal at Cosmic Dawn from the EDGES experiment opens up a new arena wherein to test models of dark matter and dark energy. Here, we consider generalized and modified Chaplygin gas models as candidate unified dark sector models. We first constrain these models against Cosmic Microwave Background data from the \textit{Planck} satellite, before exploring how the inclusion of the global 21-cm signal measured by EDGES can improve limits on the model parameters, finding that the uncertainties on the parameters of the Chaplygin gas models can be reduced by a factor between $1.5$ and $10$. We also find that within the generalized Chaplygin gas model, the tension between the CMB and local determinations of the Hubble constant $H_0$ is reduced from $\approx 4σ$ to $\approx 1.3σ$. In conclusion, we find that the global 21-cm signal at Cosmic Dawn can provide an extraordinary window onto the physics of unified dark sectors.

astro-ph.CO↗

arXiv2019

Interacting scenarios with dynamical dark energy: observational constraints and alleviation of the $H_0$ tension

We investigate interacting scenarios which belong to a wider class, since they include a dynamical dark energy component whose equation of state follows various one-parameter parametrizations. We confront them with the latest observational data from Cosmic Microwave Background (CMB), Joint light-curve (JLA) sample from Supernovae Type Ia, Baryon Acoustic Oscillations (BAO), Hubble parameter measurements from Cosmic Chronometers (CC) and a gaussian prior on the Hubble parameter $H_0$. In all examined scenarios we find a non-zero interaction, nevertheless the non-interacting case is allowed within 2$σ$. Concerning the current value of the dark energy equation of state for all combination of datasets it always lies in the phantom regime at more than two/three standard deviations. Finally, for all interacting models, independently of the combination of datasets considered, the estimated values of the present Hubble parameter $H_0$ are greater compared to the $Λ$CDM-based Planck's estimation and close to the local measurements, thus alleviating the $H_0$ tension.

astro-ph.CO↗

arXiv2019

Observational constraints on sign-changeable interaction models and alleviation of the $H_0$ tension

We investigate various scenarios which include interaction forms between dark matter and dark energy that exhibit sign reverse, namely where the transfer of energy between the dark fluids changes sign during evolution. We study the large-scale inhomogeneities in such interacting scenarios and we confront them with the latest astronomical data. Our analysis shows that the sign-changeable interaction models are able to produce stable perturbations. Additionally, the data seem to slightly favor a non-zero interaction, however, within $1σ$ confidence level (CL) the scenarios cannot be distinguished from non-interacting cosmologies. We find that the best-fit value of the dark-energy equation-of-state parameter lies in the phantom regime, while the quintessence region is also allowed nevertheless at more than 2$σ$ CL. Examining the effect of the interaction on the CMB TT and matter power spectra we show that while from the simple spectra it is hard to distinguish the interacting case from $Λ$CDM scenario, in the residual graphs the interaction is indeed traceable. Moreover, we find that sign-changeable interaction models can reconcile the $H_0$ tension, however the $σ_8$ tension is still persisting. Finally, we examine the validity of the laws of thermodynamics and we show that the generalized second law is always satisfied, while the second derivative of the total entropy becomes negative at late times which implies that the universe tends towards thermodynamic equilibrium.

astro-ph.CO↗

arXiv2019

Challenging bulk viscous unified scenarios with cosmological observations

In a spatially flat Friedmann-Lemaître-Robertson-Walker universe, we investigate a unified cosmic fluid scenario endowed with bulk viscosity in which the coefficient of the bulk viscosity has a power law evolution. The power law in the bulk viscous coefficient is a general case in this study which naturally includes several choices as special cases. Considering such a general bulk viscous scenario, in the present work we have extracted the observational constraints using the latest cosmological datasets and examine their behaviour at the level of both background and perturbations. From the observational analyses, we find that a non-zero bulk viscous coefficient is always favored and some of the models in this series are able to weaken the current tension on $H_0$ for some dataset. However, from the Bayesian evidence analysis, $Λ$CDM is favored over the bulk viscous model.

astro-ph.CO↗

arXiv2019

Reconstructing the dark matter and dark energy interaction scenarios from observations

We consider a class of interacting dark energy models in a flat and nonflat FLRW universe where the interaction is characterized by the modified evolution of the pressureless dark matter as $a^{-3+δ(a)}$, $a$ being the FLRW scale factor and $δ(a)$ quantifies the interaction rate. By assuming the most natural and nonsingular parametrization for $δ(a)$ as $δ\left( a\right) =\sum_{i} δ_i (1-a)^i $, where $δ_{i}$'s ($i=0,1,2,3,..$) are constants, we reconstruct the expansion history of the universe for three particular choices of the DE sector using different cosmological datasets. Our analyses show that the non-interacting scenario is consistent with the observations while the interaction is not strictly ruled out. We reconstruct in the following way. We start with the first two terms of $δ(a)$ above and constrain $δ_0$, $δ_1$. Then we consider up to the second order terms in $δ(a)$ but fix $δ_0$, $δ_1$ to their constrained values and constrain $δ_2$; similarly we constrain $δ_3$, and finally we constrain $(δ_0, δ_1, δ_1, δ_3)$ by keeping all of them to be free as a generalized case. Our reconstruction technique shows that the constraints on $δ_2$ (fixing $δ_0$ and $δ_1$) and $δ_3$ (fixing $δ_0$, $δ_1$ and $δ_2$) are almost zero for any interaction model and thus the effective scenario is well described by the linear parametrization $δ(a)\simeq δ_{0}+δ_{1}(1-a)$. Additionally, a strong negative correlation between $δ_0$, $δ_1$ is observed independently of the dark energy fluid and the curvature of our universe.

astro-ph.CO↗

arXiv2019

Observational constraints of a new unified dark fluid and the $H_0$ tension

Unified cosmological models have received a lot of attention in astrophysics community for explaining both the dark matter and dark energy evolution. The Chaplygin cosmologies, a well known name in this group have been investigated matched with observations from different sources. Obviously, Chaplygin cosmologies have to obey restrictions in order to be consistent with the observational data. As a consequence, alternative unified models, differing from Chaplygin model, are of special interest. In the present work we consider a specific example of such a unified cosmological model, that is quantified by only a single parameter $μ$, that can be considered as a minimal extension of the $Λ$-cold dark matter cosmology. We investigate its observational boundaries together with an analysis of the universe at large scale. Our study shows that at early time the model behaves like a dust, and as time evolves, it mimics a dark energy fluid depicting a clear transition from the early decelerating phase to the late cosmic accelerating phase. Finally, the model approaches the cosmological constant boundary in an asymptotic manner. We remark that for the present unified model, the estimations of $H_0$ are slightly higher than its local estimation and thus alleviating the $H_0$ tension.

gr-qc↗

arXiv2019

Dark sectors with dynamical coupling

Coupled dark matter-dark energy scenarios are modeled via a dimensionless parameter $ξ$, which controls the strength of their interaction. While this coupling is commonly assumed to be constant, there is no underlying physical law or symmetry that forbids a time-dependent $ξ$ parameter. The most general and complete interacting scenarios between the two dark sectors should therefore allow for such a possibility, and it is the main purpose of this study to constrain two possible and well-motivated coupled cosmologies by means of the most recent and accurate early and late-time universe observations. We find that CMB data alone prefers $ξ(z) >0$ and therefore a smaller amount of dark matter, alleviating some crucial and well-known cosmological data tensions. An objective assessment of the Bayesian evidence for the coupled models explored here shows no particular preference for the presence of a dynamical dark sector coupling.

astro-ph.CO↗

arXiv2019

Future Constraints on Dynamical Dark-Energy using Gravitational-Wave Standard Sirens

The detection of gravitational waves (GW) by the LIGO and Virgo collaborations offers a whole new range of possible tests and opens up a new window which may shed light on the nature of dark energy and dark matter. In the present work we investigate how future gravitational waves data could help to constrain different dynamical dark energy models. In particular, we perform cosmological forecastings of a class of well known and most used dynamical dark energy models using the third-generation gravitational wave detector, the Einstein Telescope. We have considered 1000 simulated GW events in order to constrain the parameter space of the dynamical dark energy models. Our analyses show that the inclusion of the GW data from the Einstein Telescope, significantly improves the parameter space of the dynamical dark energy models compared to their constraints extracted from the standard cosmological probes, namely, the cosmic microwave observations, baryon acoustic oscillations distance measurements, Supernove type Ia, and the Hubble parameter measurements.

astro-ph.CO↗

arXiv2019

Listening to the sound of dark sector interactions with gravitational wave standard sirens

We consider two stable Interacting Dark Matter -- Dark Energy models and confront them against current Cosmic Microwave Background data from the \textit{Planck} satellite. We then generate luminosity distance measurements from ${\cal O}(10^3)$ mock Gravitational Wave events matching the expected sensitivity of the proposed Einstein Telescope. We use these to forecast how the addition of Gravitational Wave standard sirens data can improve current limits on the Dark Matter -- Dark Energy coupling strength ($ξ$). We find that the addition of Gravitational Waves data can reduce the current uncertainty by a factor of $5$. Moreover, if the underlying cosmological model truly features Dark Matter -- Dark Energy interactions with a value of $ξ$ within the currently allowed $1σ$ upper limit, the addition of Gravitational Wave data would help disentangle such an interaction from the standard case of no interaction at a significance of more than $3σ$.

astro-ph.CO↗

arXiv2019

The generalized Brans-Dicke theory and its cosmology

A generalized Brans-Dicke (GBD) theory is proposed and studied in this paper. The interesting property has been found in the GBD theory, for example it can naturally solve the problem of γvalue emerging in f(R) modified gravity without introducing the so-called chameleon mechanism. In addition, it can be found that the GBD theory could solve some problems existing in other theories. (1) The $f(R)$ theory is equivalent to the BD theory with a potential (abbreviated as BDV) for taking a specific value of the BD parameter ω=0, where the specific choice: ω=0 is quite exceptional, and it is hard to understand the corresponding absence of the kinetic-energy term for the field. However, fields in the GBD own the non-disappeared dynamical effect. (2) In the double scalar-fields quintom model, it is required to include both the canonical quintessence field and the non-canonical phantom field in order to make the state parameter to cross over w=-1, while several fundamental problems are associated with phantom field, such as the problem of negative kinetic term and the fine-tuning problem, etc. While, in the GBD model, the state parameter of geometrical dark energy can cross over the phantom boundary as achieved in the quintom model, without bearing the problems existing in the quintom model. (3) The GBD theory tends to investigate the physics from the viewpoint of geometry, while the BDV or the two scalar-fields quintom model tends to solve physical problems from the viewpoint of matter. It is possible that several special characteristics of scalar fields could be revealed through studies of geometrical gravity in the GBD. As an example, we investigate the potential V of the BD scalar field, and an effective form of V could be given by studying on the GBD theory. And, it seems that a viable condition for the BD theory could be found.

gr-qc↗

arXiv2019

Constraints on quintessence scalar field models using cosmological observations

We consider a varieties of quintessence scalar field models in a homogeneous and isotropic geometry of the universe with zero spatial curvature aiming to provide stringent constraints using a series of cosmological data sets, namely, the cosmic microwave background observations (CMB), baryon acoustic oscillations (BAO), joint light curve analysis (JLA) from supernovae type Ia, redshift space distortions (RSD), and the cosmic chronometers (CC). From the qualitative evolution of the models, we find all of them are able to execute a fine transition from the past decelerating phase to the presently accelerating expansion where in addition, the equation of state of the scalar field (also the effective equation of state) might be close to that of the $Λ$CDM cosmology depending on its free parameters. From the observational analyses, we find that the scalar field parameters are unconstrained irrespective of all the observational datasets. In fact, we find that the quintessence scalar field models are pretty much determined by the CMB observations since any of the external datasets such as BAO, JLA, RSD, CC does not add any constraining power to CMB. Additionally, we observe a strong negative correlation between the parameters $H_0$ (present value of the Hubble parameter), $Ω_{m0}$ (density parameter for the matter sector, i.e., cold dark matter plus baryons) exists, while no correlation between $H_0$, and $σ_8$ (amplitude of the matter fluctuation) are not correlated. We also comment that the present models are unable to reconcile the tension on $H_0$. Finally, we conclude our work with the Bayesian analyses which report that the non-interacting $Λ$CDM model is preferred over all the quintessence scalar field models.

gr-qc↗

arXiv2019

Creating Lightweight Object Detectors with Model Compression for Deployment on Edge Devices

To achieve lightweight object detectors for deployment on the edge devices, an effective model compression pipeline is proposed in this paper. The compression pipeline consists of automatic channel pruning for the backbone, fixed channel deletion for the branch layers and knowledge distillation for the guidance learning. As results, the Resnet50-v1d is auto-pruned and fine-tuned on ImageNet to attain a compact base model as the backbone of object detector. Then, lightweight object detectors are implemented with proposed compression pipeline. For instance, the SSD-300 with model size=16.3MB, FLOPS=2.31G, and mAP=71.2 is created, revealing a better result than SSD-300-MobileNet.

cs.CV↗

arXiv2019

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.

gr-qc↗

arXiv2019

Observational constraints on one-parameter dynamical dark-energy parametrizations and the $H_0$ tension

The phenomenological parametrizations of dark-energy (DE) equation of state can be very helpful, since they allow for the investigation of its cosmological behavior despite the fact that its underlying theory is unknown. However, although there has been a large amount of research on DE parametrizations which involve two or more free parameters, the one-parameter parametrizations seem to be underestimated. We perform a detailed observational confrontation of five one-parameter DE models, with observational data from cosmic microwave background (CMB), Joint light-curve analysis sample from Supernovae Type Ia observations (JLA), baryon acoustic oscillations (BAO) distance measurements, and cosmic chronometers (CC). We find that all models favor a phantom DE equation of state at present time, while they lead to $H_0$ values in perfect agreement with its direct measurements and therefore they offer an alleviation to the $H_0$-tension. Finally, performing a Bayesian analysis we show that although $Λ$CDM cosmology is still favored, one-parameter DE models have similar or better efficiency in fitting the data comparing to two-parameter DE parametrizations, and thus they deserve a thorough investigation.

astro-ph.CO↗

arXiv2018

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 $ξ$ 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 $ξ$ but it is very small and consistent with $ξ=0$. 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 $Λ$-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.

gr-qc↗

arXiv2018

Interacting dark energy with time varying equation of state and the $H_0$ tension

Almost in all interacting dark energy models present in the literature, the stability of the model becomes potentially sensitive to the dark energy equation of state parameter $w_x$, and a singularity arises at `$w_x = -1$'. Thus, it becomes mandatory to test the stability of the model into two separate regions, namely, for quintessence and phantom. This essentially brings in a discontinuity into the parameters space for $w_x$. Such discontinuity can be removed with some specific choices of the interaction or coupling function. In the present work we choose one particular coupling between dark matter and dark energy which can successfully remove such instability and we allow a dynamical dark energy equation of state parameter instead of the constant one. In particular, considering a dynamical dark energy equation of state with only one free parameter $w_0$, representing the current value of the dark energy equation of state, we confront the interacting scenario with several observational datasets. The results show that the present cosmological data allow an interaction in the dark sector, in agreement with some latest claims by several authors, and additionally, a phantom behaviour in the dark energy equation of state is suggested at present. Moreover, for this case the tension on $H_0$ is clearly released. As a final remark, we mention that according to the Bayesian analysis, $Λ$-cold dark matter ($Λ$CDM) is always favored over this interacting dark energy model.

astro-ph.CO↗

arXiv2018

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.

gr-qc↗