arXiv subjects

Gong-Bo Zhao

Publications and source records attributed to Gong-Bo Zhao.

At least 181 records · Page 10Linked to original sources

arXiv2010

N-body Simulations for f(R) Gravity using a Self-adaptive Particle-Mesh Code

We perform high resolution N-body simulations for f(R) gravity based on a self-adaptive particle- mesh code MLAPM. The Chameleon mechanism that recovers General Relativity on small scales is fully taken into account by self-consistently solving the non-linear equation for the scalar field. We independently confirm the previous simulation results, including the matter power spectrum, halo mass function and density profiles, obtained by Oyaizu et al. (Phys.Rev.D 78, 123524, 2008) and Schmidt et al. (Phys.Rev.D 79, 083518, 2009), and extend the resolution up to k~20 h/Mpc for the measurement of the matter power spectrum. Based on our simulation results, we discuss how the Chameleon mechanism affects the clustering of dark matter and halos on full non-linear scales.

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arXiv2010

Complementarity of Weak Lensing and Peculiar Velocity Measurements in Testing General Relativity

We explore the complementarity of weak lensing and galaxy peculiar velocity measurements to better constrain modifications to General Relativity. We find no evidence for deviations from GR on cosmological scales from a combination of peculiar velocity measurements (for Luminous Red Galaxies in the Sloan Digital Sky Survey) with weak lensing measurements (from the CFHT Legacy Survey). We provide a Fisher error forecast for a Euclid-like space-based survey including both lensing and peculiar velocity measurements, and show that the expected constraints on modified gravity will be at least an order of magnitude better than with present data, i.e. we will obtain 5% errors on the modified gravity parametrization described here. We also present a model--independent method for constraining modified gravity parameters using tomographic peculiar velocity information, and apply this methodology to the present dataset.

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arXiv2010

Probing Dark Energy with the Kunlun Dark Universe Survey Telescope

Dark energy is an important science driver of many upcoming large-scale surveys. With small, stable seeing and low thermal infrared background, Dome A, Antarctica, offers a unique opportunity for shedding light on fundamental questions about the universe. We show that a deep, high-resolution imaging survey of 10,000 square degrees in \emph{ugrizyJH} bands can provide competitive constraints on dark energy equation of state parameters using type Ia supernovae, baryon acoustic oscillations, and weak lensing techniques. Such a survey may be partially achieved with a coordinated effort of the Kunlun Dark Universe Survey Telescope (KDUST) in \emph{yJH} bands over 5000--10,000 deg$^2$ and the Large Synoptic Survey Telescope in \emph{ugrizy} bands over the same area. Moreover, the joint survey can take advantage of the high-resolution imaging at Dome A to further tighten the constraints on dark energy and to measure dark matter properties with strong lensing as well as galaxy--galaxy weak lensing.

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arXiv2010

Probing modifications of General Relativity using current cosmological observations

We test General Relativity (GR) using current cosmological data: the cosmic microwave background (CMB) from WMAP5 (Komatsu et al. 2009), the integrated Sachs-Wolfe (ISW) effect from the cross-correlation of the CMB with six galaxy catalogs (Giannantonio et al. 2008), a compilation of supernovae Type Ia (SNe) including the latest SDSS SNe (Kessler et al. 2009), and part of the weak lensing (WL) data from CFHTLS (Fu et al. 2008, Kilbinger et al. 2009) that probe linear and mildly non-linear scales. We first test a model where the effective Newton's constant, mu, and the ratio of the two gravitational potentials, eta, transit from the GR value to another constant at late times; in this case, we find that standard GR is fully consistent with the combined data. The strongest constraint comes from the ISW effect which would arise from this gravitational transition; the observed ISW signal imposes a tight constraint on a combination of mu and eta that characterizes the lensing potential. Next, we consider four pixels in time and space for each function mu and eta, and perform a Principal Component Analysis (PCA) finding that seven of the resulting eight eigenmodes are consistent with GR within the errors. Only one eigenmode shows a 2-sigma deviation from the GR prediction, which is likely to be due to a systematic effect. However, the detection of such a deviation demonstrates the power of our time- and scale-dependent PCA methodology when combining observations of structure formation and expansion history to test GR.

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arXiv2010

Detecting Features in the Dark Energy Equation of State: A Wavelet Approach

We study the utility of wavelets for detecting the redshift evolution of the dark energy equation of state w(z) from the combination of supernovae, CMB and BAO data. We show that local features in w, such as bumps, can be detected efficiently using wavelets. To demonstrate, we first generate a mock supernovae (SNe) data sample for a SNAP-like survey with a bump feature in w(z) hidden in, then successfully discover it by performing a blind wavelet analysis. We also apply our method to analyze the recently released "Constitution" SNe data, combined with WMAP and BAO from SDSS, and find weak hints of dark energy dynamics. Namely, we find that models with w(z) < -1 for 0.2 < z < 0.5, and w(z)> -1 for 0.5 < z <1, are mildly favored at 95% confidence level. This is in good agreement with several recent studies using other methods, such as redshift binning with principal component analysis (PCA) (e.g. Zhao and Zhang, arXiv:0908.1568)

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arXiv2010

Probing Dark Energy Dynamics from Current and Future Cosmological Observations

We report the constraints on the dark energy equation-of-state w(z) using the latest 'Constitution' SNe sample combined with the WMAP5 and SDSS data. Based on the localized principal component analysis and the model selection criteria, we find that the LCDM model is generally consistent with the current data, yet there exists weak hint of the possible dynamics of dark energy. In particular, a model predicting w(z)<-1 at z\in[0.25,0.5) and w(z)>-1 at z\in[0.5,0.75), which means that w(z) crosses -1 in the range of z\in[0.25,0.75), is mildly favored at 95% confidence level. Given the best fit model for current data as a fiducial model, we make future forecast from the joint data sets of JDEM, Planck and LSST, and we find that the future surveys can reduce the error bars on the w bins by roughly a factor of 10 for a 5-w-bin model.

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arXiv2009

Cosmological Tests of General Relativity with Future Tomographic Surveys

Future weak lensing surveys will map the evolution of matter perturbations and gravitational potentials, yielding a new test of general relativity on cosmic scales. They will probe the relations between matter overdensities, local curvature, and the Newtonian potential. These relations can be modified in alternative gravity theories or by the effects of massive neutrinos or exotic dark energy fluids. We introduce two functions of time and scale which account for any such modifications in the linear regime. We use a principal component analysis to find the eigenmodes of these functions that cosmological data will constrain. The number of constrained modes gives a model-independent forecast of how many parameters describing deviations from general relativity could be constrained, along with $w(z)$. The modes' scale and time dependence tell us which theoretical models will be better tested.

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arXiv2009

Investigating dark energy experiments with principal components

We use a principal component approach to contrast different kinds of probes of dark energy, and to emphasize how an array of probes can work together to constrain an arbitrary equation of state history w(z). We pay particular attention to the role of the priors in assessing the information content of experiments and propose using an explicit prior on the degree of smoothness of w(z) that is independent of the binning scheme. We also show how a figure of merit based on the mean squared error probes the number of new modes constrained by a data set, and use it to examine how informative various experiments will be in constraining the evolution of dark energy.

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arXiv2009

Searching for modified growth patterns with tomographic surveys

In alternative theories of gravity, designed to produce cosmic acceleration at the current epoch, the growth of large scale structure can be modified. We study the potential of upcoming and future tomographic surveys such as DES and LSST, with the aid of CMB and supernovae data, to detect departures from the growth of cosmic structure expected within General Relativity. We employ parametric forms to quantify the potential time- and scale-dependent variation of the effective gravitational constant, and the differences between the two Newtonian potentials. We then apply the Fisher matrix technique to forecast the errors on the modified growth parameters from galaxy clustering, weak lensing, CMB, and their cross-correlations across multiple photometric redshift bins. We find that even with conservative assumptions about the data, DES will produce non-trivial constraints on modified growth, and that LSST will do significantly better.

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arXiv2008

Determining Cosmological Parameters with Latest Observational Data

In this paper, we combine the latest observational data, including the WMAP five-year data (WMAP5), BOOMERanG, CBI, VSA, ACBAR, as well as the Baryon Acoustic Oscillations (BAO) and Type Ia Supernoave (SN) "Union" compilation (307 sample) to determine the cosmological parameters. Our results show that the $Λ$CDM model remains a good fit to the current data. In a flat universe, we obtain the tight limit on the constant EoS of dark energy as, $w=-0.977\pm0.056$ ($1 σ$). For the dynamical dark energy models with time evolving EoS, we find that the best-fit values are $w_0=-1.08$ and $w_1=0.368$, implying the preference of Quintom model whose EoS gets across the cosmological constant boundary. For the curvature of universe, our results give $-0.012<Ω_k<0.009$ (95% C.L.) when fixing $w_{\DE}=-1$. When considering the dynamics of dark energy, the flat universe is still a good fit to the current data. Regarding the neutrino mass limit, we obtain the upper limits, $\sum m_ν<0.533$ eV (95% C.L.) within the framework of the flat $Λ$CDM model. When adding the SDSS Lyman-$α$ forest power spectrum data, the constraint on $\sum m_ν$ can be significantly improved, $\sum m_ν<0.161$ eV (95% C.L.). Assuming that the primordial fluctuations are adiabatic with a power law spectrum, within the $Λ$CDM model, we find that the upper limit on the ratio of the tensor to scalar is $r<0.200$ (95% C.L.) and the inflationary models with the slope $n_s\geq1$ are excluded at more than $2 σ$ confidence level. However, in the framework of dynamical dark energy models, the allowed region in the parameter space of ($n_s$,$r$) is enlarged significantly. Finally, we find no evidence for the large running of the spectral index. (Abridged)

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arXiv2008

On using the WMAP distance priors in constraining the time evolving equation of state of dark energy

Recently, the WMAP group has published their five-year data and considered the constraints on the time evolving equation of state of dark energy for the first time from the WMAP distance information. In this paper, we study the effectiveness of the usage of these distance information and find that these compressed CMB information can give similar constraints on dark energy parameters compared with the full CMB power spectrum if dark energy perturbations are included, however, once incorrectly neglecting the dark energy perturbations, the difference of the results are sizable.

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arXiv2008

High-resolution temporal constraints on the dynamics of dark energy

We use the recent type Ia supernova, cosmic microwave background and large-scale structure data to shed light on the temporal evolution of the dark energy equation of state $w(z)$ out to redshift one. We constrain the most flexible parametrization of dark energy to date, and include the dark energy perturbations consistently throughout. Interpreting our results via the principal component analysis, we find no significant evidence for dynamical dark energy: the cosmological constant model is consistent with data everywhere between redshift zero and one at 95% C.L.

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arXiv2008

Testing CPT Symmetry with CMB Measurements: Update after WMAP5

In this Letter we update our previous result on the test of CPT symmetry with Cosmic Microwave Background (CMB) measurements. A CPT violating interaction in the photon sector ${\cal L}_{cs} \sim p_μA_ν\tilde F^{μν}$ gives rise to a rotation of the polarization vectors of the propagating CMB photons. Recently the WMAP group used the newly released polarization data of WMAP5 to measure this rotation angle $Δα$ and obtained $Δα=-1.7\pm2.1$ deg ($1σ$). However, in their analysis the BOOMERanG 2003 data is not included. Here we revisit this issue by combining the full data of WMAP5 and BOOMERanG 2003 angular power spectra for the measurement of this rotation angle $Δα$ and find that $Δα=-2.6\pm1.9$ deg at a 68% confidence level.

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arXiv2008

Overcoming the Circular Problem for γ-ray Bursts in Cosmological Global Fitting Analysis

Due to the lack of low redshift long Gamma-Ray Bursts (GRBs), the circular problem has been a severe obstacle for using GRBs as cosmological candles. In this paper, we present a new method to deal with such a problem in MCMC global fitting analysis. Assuming that a certain type of correlations between different observables exists in a subsample of GRBs, for the parameters involved in the correlation relation, we treat them as free parameters and determine them simultaneously with cosmological parameters through MCMC analysis on GRB data together with other observational data. Then the circular problem is naturally eliminated in this procedure. We take the Ghirlanda relation as an example while keeping in mind the debate about its physical validity. Together with SNe Ia, WMAP and SDSS data, we include 27 GRBs with the reported Ghirlanda relation in our study, and perform MCMC global fitting. We consider the $Λ$CDM model and dynamical dark energy models. In each case, in addition to the constraints on the relevant cosmological parameters, we obtain the best fit values as well as the distributions of the correlation parameters $A$ and $C$. We find that the observational data sets other than GRBs can affect $A$ and $C$ considerably through their degeneracies with the cosmological parameters. The results on $A$ and $C$ for different cosmological models are in well agreement within $1σ$ range. The best fit value of $A$ in all models being analyzed is $A\sim 1.53$ with $σ\sim 0.08$. For $C$, we have the best value in the range of $0.94-0.98$ with $σ\sim 0.1$. It is also noted that the distributions of $A$ and $C$ are generally broader than the priors used in many studies in literature. (Abriged)

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arXiv2008

Constraints on the Sound Speed of Dynamical Dark Energy

In this paper we study the sound speed - $c_s^2$, which is directly related to the classical perturbations - of the dynamical dark energy (DE), especially with an equation of state crossing the cosmological constant boundary in details and show its implications on Cosmic Microwave Background (CMB) Anisotropy. With the present observational data of CMB, Type Ia Supernova (SNIa) and galaxy clustering, we perform a global analysis to constrain the sound speed of dark energy, using the Markov Chain Monte Carlo method. We find that the sound speed of dark energy is weakly constrained by current observations thus the futuristic precision measurements of CMB on a very large angular scale (low multipoles) are necessary.

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arXiv2008

Probing for the Cosmological Parameters with PLANCK Measurement

We investigate the constraints on cosmological parameters especially for EoS of dark energy, inflationary parameters, neutrino mass and curvature of universe using simulated Planck data. Firstly we determine cosmological parameters with current observations including ESSENCE, WMAP3, Boomerang-2K2, CBI, VSA, ACBAR, SDSS LRG and 2dFGRS, and take best-fit model as the fiducial model in simulations. In simulations we pay attention to the effects of dynamical dark energy in determination of cosmological parameters. We add simulated SNAP data to do all the simulations. Using present data, we find Quintom dark energy model is mildly favored while \LambdaCDM remains a good fit. In the framework of dynamical dark energy, the constraints on inflationary parameters, m_ν and Ω_{K} become weak compared with the constraints in \LambdaCDM. Intriguingly, we find that the inflationary models with a "blue" tilt, which are excluded about 2σin \LambdaCDM model, are well within 2σregion with the presence of the dynamics of dark energy. The upper limits of neutrino mass are weakened by a factor of 2 (95% C.L.), say, m_ν<1.59 eV and m_ν<1.53 eV for two forms of parametrization of the equation of state of dark energy. The flat universe is a good fit to the current data, namely, |Ω_{K}|<0.03 (95% C.L.). With the simulated Planck and SNAP data, dynamical dark energy and \LambdaCDM might be distinguished at 4σ. And uncertainties of inflationary parameters, m_ν and Ω_{K} can be reduced obviously. We also constrain the rotation angle Δα, denoting possible cosmological CPT violation, with simulated Planck and CMBpol data and find that our results are much more stringent than current constraint and will verify cosmological CPT symmetry with a higher precision. (Abridged)

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arXiv2007

Probing for variation of neutrino mass with current observations

With the latest astronomical data including Cosmic Microwave Background (WMAP three year, CBI, ACBAR, VSA), Type Ia Supernova ("gold sample"), Galaxy Clustering (SDSS 3-D matter power, Lyman-$α$ forest and Baryon Acoustic Oscillating (BAO)), we make a global fitting to constrain the mass varying neutrinos. We find that the parameter $δ$, denoting time evolving of neutrino mass, is weakly constrained and the neutrino mass limit today can be relaxed at least by a factor of two. Adding data of $0\nu2β$ decay of Heidelberg-Moscow experiment to our analysis, we find that $δ$ can be constrained tightly and mass varying neutrinos are favored at about 99.7% confidence level.

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arXiv2007

Cosmological neutrino mass limit and the dynamics of dark energy

We investigate the correlation between the neutrino mass limit and dark energy with time evolving equation of state. Parameterizing dark energy as w=w_0+w_1*z/(1+z), we make a global fit using Markov Chain Monte Carlo technique to determine w_0, w_1, neutrino mass as well as other cosmological parameters simultaneously. We pay particular attention to the correlation between neutrino mass Σm_ν and w_1 using current cosmological observations as well as the future simulated datasets such as PLANCK, SNAP and LAMOST.

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