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Tong-jie Zhang - One of the best experts on this subject based on the ideXlab platform.
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cosmological model independent test of varlambda cdm with two point diagnostic by the observational hubble Parameter Data
European Physical Journal C, 2018Co-Authors: Shu-lei Cao, Xiao-wei Duan, Xiao-lei Meng, Tong-jie ZhangAbstract:Aiming at exploring the nature of dark energy (DE), we use forty-three observational Hubble Parameter Data (OHD) in the redshift range $$0 < z \leqslant 2.36$$ to make a cosmological model-independent test of the $$\varLambda $$ CDM model with two-point $$Omh^2(z_{2};z_{1})$$ diagnostic. In $$\varLambda $$ CDM model, with equation of state (EoS) $$w=-1$$ , two-point diagnostic relation $$Omh^2 \equiv \varOmega _{\mathrm{m}}h^2$$ is tenable, where $$\varOmega _{\mathrm{m}}$$ is the present matter density Parameter, and h is the Hubble Parameter divided by 100 $${\mathrm {km\, s^{-1} \ Mpc^{-1}}}$$ . We utilize two methods: the weighted mean and median statistics to bin the OHD to increase the signal-to-noise ratio of the measurements. The binning methods turn out to be promising and considered to be robust. By applying the two-point diagnostic to the binned Data, we find that although the best-fit values of $$Omh^2$$ fluctuate as the continuous redshift intervals change, on average, they are continuous with being constant within 1 $$\sigma $$ confidence interval. Therefore, we conclude that the $$\varLambda $$ CDM model cannot be ruled out.
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Testing backreaction effects with observational Hubble Parameter Data
The European Physical Journal C, 2018Co-Authors: Shu-lei Cao, Hao-yi Wan, Huan-yu Teng, Tong-jie ZhangAbstract:In order to explore the generic properties of a backreaction model for explaining the accelerated expansion of the Universe, we exploit two metrics to describe the late time Universe. Since the standard FLRW metric cannot precisely describe the late time Universe on small scales, the template metric with an evolving curvature Parameter $\kappa_{\mathcal{D}}(t)$ is employed. However, we doubt the validity of the prescription for $\kappa_{\mathcal{D}}$, which motivates us apply observational Hubble Parameter Data (OHD) to constrain Parameters in dust cosmology. First, for FLRW metric, by getting best-fit constraints of $\Omega^{\mathcal{D}_0}_m = 0.25^{+0.03}_{-0.03}$, $n = 0.02^{+0.69}_{-0.66}$, and $H_{\mathcal{D}_0} = 70.54^{+4.24}_{-3.97}\ {\rm km \ s^{-1} \ Mpc^{-1}}$, the evolutions of Parameters are explored. Second, in template metric context, by marginalizing over $H_{\mathcal{D}_0}$ as a prior of uniform distribution, we obtain the best-fit values of $n=-1.22^{+0.68}_{-0.41}$ and ${{\Omega}_{m}^{\mathcal{D}_{0}}}=0.12^{+0.04}_{-0.02}$. Moreover, we utilize three different Gaussian priors of $H_{\mathcal{D}_0}$, which result in different best-fits of $n$, but almost the same best-fit value of ${{\Omega}_{m}^{\mathcal{D}_{0}}}\sim0.12$. Also, the absolute constraints without marginalization of Parameter are obtained: $n=-1.1^{+0.58}_{-0.50}$ and ${{\Omega}_{m}^{\mathcal{D}_{0}}}=0.13\pm0.03$. With these constraints, the evolutions of the effective deceleration Parameter $q^{\mathcal{D}}$ indicate that the backreaction can account for the accelerated expansion of the Universe without involving extra dark energy component in the scaling solution context. Nevertheless, the results also verify that the prescription of $\kappa_{\mathcal{D}}$ is insufficient and should be improved.
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testing backreaction effects with observational hubble Parameter Data
European Physical Journal C, 2018Co-Authors: Shu-lei Cao, Hao-yi Wan, Huan-yu Teng, Tong-jie ZhangAbstract:The spatially averaged inhomogeneous Universe includes a kinematical backreaction term $${\mathcal {Q}}_{\mathcal {D}}$$ that is relate to the averaged spatial Ricci scalar $${\langle \mathcal {R}} \rangle _{\mathcal {D}}$$ in the framework of general relativity. Under the assumption that $${\mathcal {Q}}_{\mathcal {D}}$$ and $${\langle \mathcal {R}} \rangle _{\mathcal {D}}$$ obey the scaling laws of the volume scale factor $$a_{\mathcal {D}}$$ , a direct coupling between them with a scaling index n is remarkable. In order to explore the generic properties of a backreaction model for explaining the accelerated expansion of the Universe, we exploit two metrics to describe the late time Universe. Since the standard FLRW metric cannot precisely describe the late time Universe on small scales, the template metric with an evolving curvature Parameter $$\kappa _{\mathcal {D}}(t)$$ is employed. However, we doubt the validity of the prescription for $$\kappa _{\mathcal {D}}$$ , which motivates us apply observational Hubble Parameter Data (OHD) to constrain Parameters in dust cosmology. First, for FLRW metric, by getting best-fit constraints of $$\varOmega ^{{\mathcal {D}}_0}_m = 0.25^{+0.03}_{-0.03}$$ , $$n = 0.02^{+0.69}_{-0.66}$$ , and $$H_{\mathcal {D}_0} = 70.54^{+4.24}_{-3.97}\ \mathrm{km \ s^{-1} \ Mpc^{-1}}$$ , the evolutions of Parameters are explored. Second, in template metric context, by marginalizing over $$H_{\mathcal {D}_0}$$ as a prior of uniform distribution, we obtain the best-fit values of $$n=-1.22^{+0.68}_{-0.41}$$ and $${{\varOmega }_{m}^{\mathcal {D}_{0}}}=0.12^{+0.04}_{-0.02}$$ . Moreover, we utilize three different Gaussian priors of $$H_{\mathcal {D}_0}$$ , which result in different best-fits of n, but almost the same best-fit value of $${{\varOmega }_{m}^{\mathcal {D}_{0}}}\sim 0.12$$ . Also, the absolute constraints without marginalization of Parameter are obtained: $$n=-1.1^{+0.58}_{-0.50}$$ and $${{\varOmega }_{m}^{\mathcal {D}_{0}}}=0.13\pm 0.03$$ . With these constraints, the evolutions of the effective deceleration Parameter $$q^{\mathcal {D}}$$ indicate that the backreaction can account for the accelerated expansion of the Universe without involving extra dark energy component in the scaling solution context. Nevertheless, the results also verify that the prescription of $$\kappa _{\mathcal {D}}$$ is insufficient and should be improved.
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cosmological model independent test of lambda cdm with two point diagnostic by the observational hubble Parameter Data
arXiv: Cosmology and Nongalactic Astrophysics, 2017Co-Authors: Shu-lei Cao, Xiao-wei Duan, Xiao-lei Meng, Tong-jie ZhangAbstract:Aiming at exploring the nature of dark energy (DE), we use forty-three observational Hubble Parameter Data (OHD) in the redshift range $0 < z \leqslant 2.36$ to make a cosmological model-independent test of the $\Lambda$CDM model with two-point $Omh^2(z_{2};z_{1})$ diagnostic. In $\Lambda$CDM model, with equation of state (EoS) $w=-1$, two-point diagnostic relation $Omh^2 \equiv \Omega_m h^2$ is tenable, where $\Omega_m$ is the present matter density Parameter, and $h$ is the Hubble Parameter divided by 100 $\rm km s^{-1} Mpc^{-1}$. We utilize two methods: the weighted mean and median statistics to bin the OHD to increase the signal-to-noise ratio of the measurements. The binning methods turn out to be promising and considered to be robust. By applying the two-point diagnostic to the binned Data, we find that although the best-fit values of $Omh^2$ fluctuate as the continuous redshift intervals change, on average, they are continuous with being constant within 1 $\sigma$ confidence interval. Therefore, we conclude that the $\Lambda$CDM model cannot be ruled out.
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Direct reconstruction of dynamical dark energy from observational Hubble Parameter Data
Physics of the Dark Universe, 2016Co-Authors: Zhi-e Liu, Tong-jie Zhang, Yan-ke TangAbstract:Abstract Reconstructing the evolution history of the dark energy equation of state Parameter w ( z ) directly from observational Data is highly valuable in cosmology, since it contains substantial clues in understanding the nature of the accelerated expansion of the Universe. Many works have focused on reconstructing w ( z ) using Type Ia supernova Data, however, only a few studies pay attention to Hubble Parameter Data. In the present work, we explore the merit of Hubble Parameter Data and make an attempt to reconstruct w ( z ) from them through the principle component analysis approach. We find that current Hubble Parameter Data perform well in reconstructing w ( z ) ; though, when compared to supernova Data, the Data are scant and their quality is worse. Both Λ CDM and evolving w ( z ) models can be constrained within 10 % at redshifts z ≲ 1.5 and even 5 % at redshifts 0.1 ≲ z ≲ 1 by using simulated H ( z ) Data of observational quality.
Bharat Ratra - One of the best experts on this subject based on the ideXlab platform.
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using pantheon and des supernova baryon acoustic oscillation and hubble Parameter Data to constrain the hubble constant dark energy dynamics and spatial curvature
Monthly Notices of the Royal Astronomical Society, 2021Co-Authors: Shu-lei Cao, Joseph V Ryan, Bharat RatraAbstract:We use Pantheon Type Ia supernova (SN Ia) apparent magnitude, DES-3yr binned SN Ia apparent magnitude, Hubble Parameter, and baryon acoustic oscillation measurements to constrain six spatially flat and non-flat cosmological models. These sets of Data provide mutually consistent cosmological constraints in the six cosmological models we study. A joint analysis of these Data sets provides model-independent estimates of the Hubble constant, $H_0=68.8\pm1.8\ \rm{km \ s^{-1} \ Mpc^{-1}}$, and the non-relativistic matter density Parameter, $\Omega_{\rm m_0}=0.294\pm0.020$. Although the joint constraints prefer mild dark energy dynamics and a little spatial curvature, they do not rule out dark energy being a cosmological constant and flat spatial hypersurfaces. We also add quasar angular size and H II starburst galaxy measurements to the combined Data set and find more restrictive constraints.
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measuring the hubble constant and spatial curvature from supernova apparent magnitude baryon acoustic oscillation and hubble Parameter Data
Astrophysics and Space Science, 2019Co-Authors: Changyung Park, Bharat RatraAbstract:Cosmic microwave background (CMB) anisotropy (spatial inhomogeneity) Data provide the tightest constraints on the Hubble constant, matter density, spatial curvature, and dark energy dynamics. Other Data, sensitive to the evolution of only the spatially homogeneous part of the cosmological model, such as Type Ia supernova apparent magnitude, baryon acoustic oscillation distance, and Hubble Parameter measurements, can be used in conjunction with the CMB Data to more tightly constrain Parameters. Recent joint analyses of CMB and such non-CMB Data indicate that slightly closed spatial hypersurfaces are favored in nonflat untilted inflation models and that dark energy dynamics cannot be ruled out, and favor a smaller Hubble constant. We show that the constraints that follow from these non-CMB Data alone are consistent with those that follow from the CMB Data alone and so also consistent with, but weaker than, those that follow from the joint analyses of the CMB and non-CMB Data.
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Constraints on dark energy dynamics and spatial curvature from Hubble Parameter and baryon acoustic oscillation Data
Monthly Notices of the Royal Astronomical Society, 2018Co-Authors: Joseph Ryan, Sanket Doshi, Bharat RatraAbstract:We use all available baryon acoustic oscillation distance measurements and Hubble Parameter Data to constrain the cosmological constant $\Lambda$, dynamical dark energy, and spatial curvature in simple cosmological models. We find that the consensus spatially flat $\Lambda$CDM model provides a reasonable fit to the Data, but depending on the Hubble constant prior and cosmological model, it can be a little more than 1$\sigma$ away from the best-fit model, which can favor mild dark energy dynamics or non-flat spatial hypersurfaces.
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Hubble Parameter Data constraints on dark energy
Physics Letters B, 2011Co-Authors: Yun Chen, Bharat RatraAbstract:Abstract We use Hubble Parameter versus redshift Data from Stern et al. (2010) [1] and Gaztanaga et al. (2009) [2] to place constraints on model Parameters of constant and time-evolving dark energy cosmological models. These constraints are consistent with (through not as restrictive as) those derived from supernova Type Ia magnitude-redshift Data. However, they are more restrictive than those derived from galaxy cluster angular diameter distance, and comparable with those from gamma-ray burst and lookback time Data. A joint analysis of the Hubble Parameter Data with more restrictive baryon acoustic oscillation peak length scale and supernova Type Ia apparent magnitude Data favors a spatially-flat cosmological model currently dominated by a time-independent cosmological constant but does not exclude time-varying dark energy.
Shuo Yuan - One of the best experts on this subject based on the ideXlab platform.
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breaking through the high redshift bottleneck of observational hubble Parameter Data the sandage loeb signal scheme
Journal of Cosmology and Astroparticle Physics, 2015Co-Authors: Shuo Yuan, Tong-jie ZhangAbstract:We propose a robust scheme to measure the Hubble Parameter H(z) at high redshifts by detecting the Sandage-Loeb signal (SL signal) which can be realized by the next generation extremely large telescope. It will largely extend the current observational Hubble Parameter Data (OHD) towards the redshift range of z [2.0,5.0] where other dark energy probes is difficult to provide useful information of the cosmic expansion. To quantify the capability of such future measurement to constrain cosmological models, we simulate observational Data for a CODEX (COsmic Dynamics and EXo-earth experiment)-like survey. We find that the SL signal scheme brings the redshift upper-limit of OHD from zmax = 2.3 to 0zmax 5., provides more accurate constraints on different dark energy models, and greatly changes the degeneracy direction of the Parameters. For the ΛCDM case, the accuracy of Ωm is improved by 58% and the degeneracy between Ωm and ΩΛ is rotated to the vertical direction of Ωm − ΩΛ plane; for the wCDM case, the accuracy of w is improved by 15%. The Fisher matrix forecast on different time-dependent w(z) cosmological model is also performed.
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Breaking through the high redshift bottleneck of Observational Hubble Parameter Data: The Sandage-Loeb signal Scheme
Journal of Cosmology and Astroparticle Physics, 2015Co-Authors: Shuo Yuan, Siqi Liu, Tong-jie ZhangAbstract:We propose a valid scheme to measure the Hubble Parameter $H(z)$ at high redshifts by detecting the Sandage-Loeb signal (SL signal) which can be realized by the next generation extremely large telescope. It will largely extend the current observational Hubble Parameter Data (OHD) towards the redshift region of $z \in [2.0,5.0]$, the so-called "redshift desert", where other dark energy probes are hard to provide useful information of the cosmic expansion. Quantifying the ability of this future measurement by simulating observational Data for a CODEX (COsmic Dynamics and EXo-earth experiment)-like survey and constraining various cosmological models, we find that the SL signal scheme brings the redshift upper-limit of OHD from $z_\mathrm{max}=2.3$ to $z_\mathrm{max}\simeq 5.0$, provides more accurate constraints on different dark energy models, and greatly changes the degeneracy direction of the Parameters. For the $\Lambda$CDM case, the accuracy of $\Omega_m$ is improved by $58\%$ and the degeneracy between $\Omega_m$ and $\Omega_ {\Lambda}$ is rotated to the vertical direction of $\Omega_k = 0$ line strongly; for the $w$CDM case, the accuracy of $w$ is improved by $15\%$. The Fisher matrix forecast on different time-dependent $w(z)$ is also performed.
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Nonparametric reconstruction of dynamical dark energy via observational Hubble Parameter Data
Physical Review D, 2013Co-Authors: Shuo Yuan, Tong-jie ZhangAbstract:We study the power of current and future observational Hubble Parameter Data (OHD) on non-parametric estimations of the dark energy equation of state, $w(z)$. We propose a new method by conjunction of principal component analysis (PCA) and the criterion of goodness of fit (GoF) criterion to reconstruct $w(z)$, ensuring the sensitivity and reliability of the extraction of features in the EoS. We also give an new error model to simulate future OHD Data, to forecast the power of future OHD on the EoS reconstruction. The result shows that current OHD, despite in less quantity, give not only a similar power of reconstruction of dark energy compared to the result given by type Ia supernovae, but also extend the constraint on $w(z)$ up to redshift $z\simeq2$. Additionally, a reasonable forecast of future Data in more quantity and better quality greatly enhances the reconstruction of dark energy.
Shu-lei Cao - One of the best experts on this subject based on the ideXlab platform.
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using pantheon and des supernova baryon acoustic oscillation and hubble Parameter Data to constrain the hubble constant dark energy dynamics and spatial curvature
Monthly Notices of the Royal Astronomical Society, 2021Co-Authors: Shu-lei Cao, Joseph V Ryan, Bharat RatraAbstract:We use Pantheon Type Ia supernova (SN Ia) apparent magnitude, DES-3yr binned SN Ia apparent magnitude, Hubble Parameter, and baryon acoustic oscillation measurements to constrain six spatially flat and non-flat cosmological models. These sets of Data provide mutually consistent cosmological constraints in the six cosmological models we study. A joint analysis of these Data sets provides model-independent estimates of the Hubble constant, $H_0=68.8\pm1.8\ \rm{km \ s^{-1} \ Mpc^{-1}}$, and the non-relativistic matter density Parameter, $\Omega_{\rm m_0}=0.294\pm0.020$. Although the joint constraints prefer mild dark energy dynamics and a little spatial curvature, they do not rule out dark energy being a cosmological constant and flat spatial hypersurfaces. We also add quasar angular size and H II starburst galaxy measurements to the combined Data set and find more restrictive constraints.
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cosmological model independent test of varlambda cdm with two point diagnostic by the observational hubble Parameter Data
European Physical Journal C, 2018Co-Authors: Shu-lei Cao, Xiao-wei Duan, Xiao-lei Meng, Tong-jie ZhangAbstract:Aiming at exploring the nature of dark energy (DE), we use forty-three observational Hubble Parameter Data (OHD) in the redshift range $$0 < z \leqslant 2.36$$ to make a cosmological model-independent test of the $$\varLambda $$ CDM model with two-point $$Omh^2(z_{2};z_{1})$$ diagnostic. In $$\varLambda $$ CDM model, with equation of state (EoS) $$w=-1$$ , two-point diagnostic relation $$Omh^2 \equiv \varOmega _{\mathrm{m}}h^2$$ is tenable, where $$\varOmega _{\mathrm{m}}$$ is the present matter density Parameter, and h is the Hubble Parameter divided by 100 $${\mathrm {km\, s^{-1} \ Mpc^{-1}}}$$ . We utilize two methods: the weighted mean and median statistics to bin the OHD to increase the signal-to-noise ratio of the measurements. The binning methods turn out to be promising and considered to be robust. By applying the two-point diagnostic to the binned Data, we find that although the best-fit values of $$Omh^2$$ fluctuate as the continuous redshift intervals change, on average, they are continuous with being constant within 1 $$\sigma $$ confidence interval. Therefore, we conclude that the $$\varLambda $$ CDM model cannot be ruled out.
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Testing backreaction effects with observational Hubble Parameter Data
The European Physical Journal C, 2018Co-Authors: Shu-lei Cao, Hao-yi Wan, Huan-yu Teng, Tong-jie ZhangAbstract:In order to explore the generic properties of a backreaction model for explaining the accelerated expansion of the Universe, we exploit two metrics to describe the late time Universe. Since the standard FLRW metric cannot precisely describe the late time Universe on small scales, the template metric with an evolving curvature Parameter $\kappa_{\mathcal{D}}(t)$ is employed. However, we doubt the validity of the prescription for $\kappa_{\mathcal{D}}$, which motivates us apply observational Hubble Parameter Data (OHD) to constrain Parameters in dust cosmology. First, for FLRW metric, by getting best-fit constraints of $\Omega^{\mathcal{D}_0}_m = 0.25^{+0.03}_{-0.03}$, $n = 0.02^{+0.69}_{-0.66}$, and $H_{\mathcal{D}_0} = 70.54^{+4.24}_{-3.97}\ {\rm km \ s^{-1} \ Mpc^{-1}}$, the evolutions of Parameters are explored. Second, in template metric context, by marginalizing over $H_{\mathcal{D}_0}$ as a prior of uniform distribution, we obtain the best-fit values of $n=-1.22^{+0.68}_{-0.41}$ and ${{\Omega}_{m}^{\mathcal{D}_{0}}}=0.12^{+0.04}_{-0.02}$. Moreover, we utilize three different Gaussian priors of $H_{\mathcal{D}_0}$, which result in different best-fits of $n$, but almost the same best-fit value of ${{\Omega}_{m}^{\mathcal{D}_{0}}}\sim0.12$. Also, the absolute constraints without marginalization of Parameter are obtained: $n=-1.1^{+0.58}_{-0.50}$ and ${{\Omega}_{m}^{\mathcal{D}_{0}}}=0.13\pm0.03$. With these constraints, the evolutions of the effective deceleration Parameter $q^{\mathcal{D}}$ indicate that the backreaction can account for the accelerated expansion of the Universe without involving extra dark energy component in the scaling solution context. Nevertheless, the results also verify that the prescription of $\kappa_{\mathcal{D}}$ is insufficient and should be improved.
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testing backreaction effects with observational hubble Parameter Data
European Physical Journal C, 2018Co-Authors: Shu-lei Cao, Hao-yi Wan, Huan-yu Teng, Tong-jie ZhangAbstract:The spatially averaged inhomogeneous Universe includes a kinematical backreaction term $${\mathcal {Q}}_{\mathcal {D}}$$ that is relate to the averaged spatial Ricci scalar $${\langle \mathcal {R}} \rangle _{\mathcal {D}}$$ in the framework of general relativity. Under the assumption that $${\mathcal {Q}}_{\mathcal {D}}$$ and $${\langle \mathcal {R}} \rangle _{\mathcal {D}}$$ obey the scaling laws of the volume scale factor $$a_{\mathcal {D}}$$ , a direct coupling between them with a scaling index n is remarkable. In order to explore the generic properties of a backreaction model for explaining the accelerated expansion of the Universe, we exploit two metrics to describe the late time Universe. Since the standard FLRW metric cannot precisely describe the late time Universe on small scales, the template metric with an evolving curvature Parameter $$\kappa _{\mathcal {D}}(t)$$ is employed. However, we doubt the validity of the prescription for $$\kappa _{\mathcal {D}}$$ , which motivates us apply observational Hubble Parameter Data (OHD) to constrain Parameters in dust cosmology. First, for FLRW metric, by getting best-fit constraints of $$\varOmega ^{{\mathcal {D}}_0}_m = 0.25^{+0.03}_{-0.03}$$ , $$n = 0.02^{+0.69}_{-0.66}$$ , and $$H_{\mathcal {D}_0} = 70.54^{+4.24}_{-3.97}\ \mathrm{km \ s^{-1} \ Mpc^{-1}}$$ , the evolutions of Parameters are explored. Second, in template metric context, by marginalizing over $$H_{\mathcal {D}_0}$$ as a prior of uniform distribution, we obtain the best-fit values of $$n=-1.22^{+0.68}_{-0.41}$$ and $${{\varOmega }_{m}^{\mathcal {D}_{0}}}=0.12^{+0.04}_{-0.02}$$ . Moreover, we utilize three different Gaussian priors of $$H_{\mathcal {D}_0}$$ , which result in different best-fits of n, but almost the same best-fit value of $${{\varOmega }_{m}^{\mathcal {D}_{0}}}\sim 0.12$$ . Also, the absolute constraints without marginalization of Parameter are obtained: $$n=-1.1^{+0.58}_{-0.50}$$ and $${{\varOmega }_{m}^{\mathcal {D}_{0}}}=0.13\pm 0.03$$ . With these constraints, the evolutions of the effective deceleration Parameter $$q^{\mathcal {D}}$$ indicate that the backreaction can account for the accelerated expansion of the Universe without involving extra dark energy component in the scaling solution context. Nevertheless, the results also verify that the prescription of $$\kappa _{\mathcal {D}}$$ is insufficient and should be improved.
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cosmological model independent test of lambda cdm with two point diagnostic by the observational hubble Parameter Data
arXiv: Cosmology and Nongalactic Astrophysics, 2017Co-Authors: Shu-lei Cao, Xiao-wei Duan, Xiao-lei Meng, Tong-jie ZhangAbstract:Aiming at exploring the nature of dark energy (DE), we use forty-three observational Hubble Parameter Data (OHD) in the redshift range $0 < z \leqslant 2.36$ to make a cosmological model-independent test of the $\Lambda$CDM model with two-point $Omh^2(z_{2};z_{1})$ diagnostic. In $\Lambda$CDM model, with equation of state (EoS) $w=-1$, two-point diagnostic relation $Omh^2 \equiv \Omega_m h^2$ is tenable, where $\Omega_m$ is the present matter density Parameter, and $h$ is the Hubble Parameter divided by 100 $\rm km s^{-1} Mpc^{-1}$. We utilize two methods: the weighted mean and median statistics to bin the OHD to increase the signal-to-noise ratio of the measurements. The binning methods turn out to be promising and considered to be robust. By applying the two-point diagnostic to the binned Data, we find that although the best-fit values of $Omh^2$ fluctuate as the continuous redshift intervals change, on average, they are continuous with being constant within 1 $\sigma$ confidence interval. Therefore, we conclude that the $\Lambda$CDM model cannot be ruled out.
Zong-hong Zhu - One of the best experts on this subject based on the ideXlab platform.
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Testing cosmic opacity from SNe Ia and Hubble Parameter through three cosmological-model-independent methods
Physics Letters B, 2013Co-Authors: Kai Liao, Jing Ming, Zong-hong ZhuAbstract:AbstractWe use the newly published 28 observational Hubble Parameter Data (H(z)) and current largest SNe Ia samples (Union2.1) to test whether the universe is transparent. Three cosmological-model-independent methods (nearby SNe Ia method, interpolation method and smoothing method) are proposed through comparing opacity-free distance modulus from Hubble Parameter Data and opacity-dependent distance modulus from SNe Ia. Two Parameterizations, τ(z)=2ϵz and τ(z)=(1+z)2ϵ−1 are adopted for the optical depth associated to the cosmic absorption. We find that the results are not sensitive to the methods and Parameterizations. Our results support a transparent universe
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observational constraints on unified dark matter including hubble Parameter Data
Physics Letters B, 2012Co-Authors: Kai Liao, Shuo Cao, Jun Wang, Xiaolong Gong, Zong-hong ZhuAbstract:Abstract We constrain a unified dark matter (UDM) model from the latest observational Data. This model assumes that the dark sector is degenerate. Dark energy and dark matter are the same component. It can be described by an affine equation of state P X = p 0 + α ρ X . Our Data set contains the newly revised H ( z ) Data, type Ia supernovae (SNe Ia) from Union2 set, baryonic acoustic oscillation (BAO) observation from the spectroscopic Sloan Digital Sky Survey (SDSS) Data release 7 (DR7) galaxy sample, as well as the cosmic microwave background (CMB) observation from the 7-year Wilkinson Microwave Anisotropy Probe (WMAP7) results. By using the Markov Chain Monte Carlo (MCMC) method, we obtain the results in a flat universe: Ω Λ = 0.719 − 0.0305 + 0.0264 ( 1 σ ) − 0.0458 + 0.0380 ( 2 σ ) , α = 1.72 − 4.79 + 3.92 ( 1 σ ) − 7.30 + 5.47 ( 2 σ ) ( × 10 − 3 ) , Ω b h 2 = 0.0226 − 0.0011 + 0.0011 ( 1 σ ) − 0.0015 + 0.0016 ( 2 σ ) . Moreover, when considering a non-flat universe, Ω Λ = 0.722 − 0.0447 + 0.0362 ( 1 σ ) − 0.0634 + 0.0479 ( 2 σ ) , α = 0.242 − 0.775 + 0.787 ( 1 σ ) − 1.03 + 1.10 ( 2 σ ) ( × 10 − 2 ) , Ω b h 2 = 0.0227 − 0.0014 + 0.0015 ( 1 σ ) − 0.0018 + 0.0021 ( 2 σ ) , Ω k = − 0.194 − 1.85 + 2.02 ( 1 σ ) − 2.57 + 2.75 ( 2 σ ) ( × 10 − 2 ) . These give a more stringent results than before. We also give the results from other combinations of these Data for comparison. The observational Hubble Parameter Data can give a more stringent constraint than SNe Ia. From the constraint results, we can see the Parameters α and Ω k are very close to zero, which means a flat universe is strongly supported and the speed of sound of the dark sector seems to be zero.
