arXiv subjects

Kai Liao

Publications and source records attributed to Kai Liao.

83 records · Page 5Linked to original sources

arXiv2014

Strong Lens Time Delay Challenge: I. Experimental Design

The time delays between point-like images in gravitational lens systems can be used to measure cosmological parameters. The number of lenses with measured time delays is growing rapidly; the upcoming \emph{Large Synoptic Survey Telescope} (LSST) will monitor $\sim10^3$ strongly lensed quasars. In an effort to assess the present capabilities of the community to accurately measure the time delays, and to provide input to dedicated monitoring campaigns and future LSST cosmology feasibility studies, we have invited the community to take part in a "Time Delay Challenge" (TDC). The challenge is organized as a set of "ladders," each containing a group of simulated datasets to be analyzed blindly by participating teams. Each rung on a ladder consists of a set of realistic mock observed lensed quasar light curves, with the rungs' datasets increasing in complexity and realism. The initial challenge described here has two ladders, TDC0 and TDC1. TDC0 has a small number of datasets, and is designed to be used as a practice set by the participating teams. The (non-mandatory) deadline for completion of TDC0 was the TDC1 launch date, December 1, 2013. The TDC1 deadline was July 1 2014. Here we give an overview of the challenge, we introduce a set of metrics that will be used to quantify the goodness-of-fit, efficiency, precision, and accuracy of the algorithms, and we present the results of TDC0. Thirteen teams participated in TDC0 using 47 different methods. Seven of those teams qualified for TDC1, which is described in the companion paper II.

astro-ph.IM↗

arXiv2014

Strong Lens Time Delay Challenge: II. Results of TDC1

We present the results of the first strong lens time delay challenge. The motivation, experimental design, and entry level challenge are described in a companion paper. This paper presents the main challenge, TDC1, which consisted of analyzing thousands of simulated light curves blindly. The observational properties of the light curves cover the range in quality obtained for current targeted efforts (e.g.,~COSMOGRAIL) and expected from future synoptic surveys (e.g.,~LSST), and include simulated systematic errors. \nteamsA\ teams participated in TDC1, submitting results from \nmethods\ different method variants. After a describing each method, we compute and analyze basic statistics measuring accuracy (or bias) $A$, goodness of fit $χ^2$, precision $P$, and success rate $f$. For some methods we identify outliers as an important issue. Other methods show that outliers can be controlled via visual inspection or conservative quality control. Several methods are competitive, i.e., give $|A|<0.03$, $P<0.03$, and $χ^2<1.5$, with some of the methods already reaching sub-percent accuracy. The fraction of light curves yielding a time delay measurement is typically in the range $f = $20--40\%. It depends strongly on the quality of the data: COSMOGRAIL-quality cadence and light curve lengths yield significantly higher $f$ than does sparser sampling. Taking the results of TDC1 at face value, we estimate that LSST should provide around 400 robust time-delay measurements, each with $P<0.03$ and $|A|<0.01$, comparable to current lens modeling uncertainties. In terms of observing strategies, we find that $A$ and $f$ depend mostly on season length, while P depends mostly on cadence and campaign duration.

astro-ph.IM↗

arXiv2013

A Consistent Test of the Distance-Duality Relation with Galaxy Clusters and Type Ia Supernave

We propose a new consistent method to test of the distance-duality (DD) relation which related angular diameter distances (DA) to the luminosity distances (DL) in a cosmology-independent way. In order to avoid any bias brought by redshift incoincidence between galaxy clusters and Type Ia Supernave (SNe Ia), as well as to ensure the integrity of the galaxy clusters samples, we obtain the luminosity distance of a certain SN Ia point at the same redshift of the corresponding galaxy cluster by interpolating from the nearby SNe Ia. With the observational data at the same redshifts of the angular diameter distances from the complete 38 galaxy cluster sample for the spherical model and the corrected luminosity distances interpolated from the Union2 set, we find that $η\equiv {D_L}{(1+z)}^{-2}/{D_A}=1$ is satisfied within $2σ$ confidence level for various parameterizations of $η(z)$, which are more stringent than previous testing results without considering redshift bias.

astro-ph.CO↗

arXiv2013

Probing modified gravity theories with the Sandage-Loeb test

In this paper, we quantify the ability of a future measurement of the Sandage-Loeb test signal from the Cosmic-Dynamic-Experiment-like spectrograph to constrain some popular modified gravity theories including DGP brane-world scenario, $f(R)$ modified gravity and $f(T)$ gravity theory. We find that the Sandage-Loeb test measurements are able to break degeneracies between model parameters markedly and thus greatly improve cosmological constraints for all concerned modified gravity theories when combined with the latest observations of CMB--shift parameter. However, they yield almost the same degeneracy directions between model parameters as that from the distance ratio data derived from the latest observations of the cosmic microwave background and baryonic acoustic oscillations (CMB/BAO). Moreover, for the $f(R)$ modified gravity, the Sandage-Loeb test could provide completely different bounded regions in model parameters space as compared to CMB/BAO and thus supplement strong complementary constraints.

gr-qc↗

arXiv2012

Testing cosmic opacity from SNe Ia and Hubble parameter through three cosmological-model-independent methods

We 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.

astro-ph.CO↗

arXiv2012

A unification of RDE model and XCDM model

In this Letter, we propose a new generalized Ricci dark energy (NGR) model to unify Ricci dark energy (RDE) and XCDM. Our model can distinguish between RDE and XCDM by introducing a parameter $β$ called weight factor. When $β=1$, NGR model becomes the usual RDE model. The XCDM model is corresponding to $β=0$. Moreover, NGR model permits the situation where neither $β=1$ nor $β=0$. We then perform a statefinder analysis on NGR model to see how $β$ effects the trajectory on the $r-s$ plane. In order to know the value of $β$, we constrain NGR model with latest observations including type Ia supernovae (SNe Ia) from Union2 set (557 data), baryonic acoustic oscillation (BAO) observation from the spectroscopic Sloan Digital Sky Survey (SDSS) data release 7 (DR7) galaxy sample and cosmic microwave background (CMB) observation from the 7-year Wilkinson Microwave Anisotropy Probe (WMAP7) results. With Markov Chain Monte Carlo (MCMC) method, the constraint result is $β$=$0.08_{-0.21}^{+0.30}(1σ)_{-0.28}^{+0.43}(2σ)$, which manifests the observations prefer a XCDM universe rather than RDE model. It seems RDE model is ruled out in NGR scenario within $2σ$ regions. Furthermore, we compare it with some of successful cosmological models using AIC information criterion. NGR model seems to be a good choice for describing the universe.

astro-ph.CO↗

arXiv2012

Energy conditions in $f(R,L_{m})$ gravity

In order to constrain $f(R,L_{m})$ gravity from theoretical aspects, its energy conditions are derived in this paper. These energy conditions given by us are quite general and can be degenerated to the well-known energy conditions in General Relativity and $f(R)$ theories of gravity with arbitrary coupling, non-minimal coupling and non-coupling between matter and geometry, respectively, as special cases. To exemplify how to use these energy conditions to restrict $f(R,L_{m})$ gravity, we consider a special model in the FRW cosmology and give some corresponding results by using astronomical observations.

physics.gen-ph↗

arXiv2012

Testing the interaction model with cosmological data and gamma-ray bursts

We use the new gamma-ray bursts (GRBs) data, combined with the baryon acoustic oscillation(BAO) observation from the spectroscopic Sloan Digital Sky Survey (SDSS) data release, the newly obtained $A$ parameter at $z=0.6$ from the WiggleZ Dark Energy Survey, the cosmic microwave background (CMB) observations from the 7-Year Wilkinson Microwave Anisotropy Probe (WMAP7) results, and the type Ia supernovae (SNeIa) from Union2 set, to constrain a phenomenological model describing possible interactions between dark energy and dark matter, which was proposed to alleviate the coincidence problem of the standard $Λ$CDM model. By using the Markov Chain Monte Carlo (MCMC) method, we obtain the marginalized $1σ$ constraints $Ω_{m}=0.2886\pm{0.0135}$, $r_m=-0.0047\pm{0.0046}$, and $w_X=-1.0658\pm{0.0564}$. We also consider other combinations of these data for comparison. These results show that: (1) the energy of dark matter is slightly transferring to that of dark energy; (2) even though the GRBs+BAO+CMB data present less stringent constraints than SNe+BAO+CMB data do, the GRBs can help eliminate the degeneracies among parameters.

astro-ph.CO↗

arXiv2012

Observational constraints on new generalized Chaplygin gas model

We use the latest data to investigate observational constraints on the new generalized Chaplygin gas (NGCG) model. Using the Markov Chain Monte Carlo (MCMC) method, we constrain the NGCG model with the type Ia supernovae (SNe Ia) from Union2 set (557 data), the usual baryonic acoustic oscillation (BAO) observation from the spectroscopic Sloan Digital Sky Survey (SDSS) data release 7 (DR7) galaxy sample, the cosmic microwave background (CMB) observation from the 7-year Wilkinson Microwave Anisotropy Probe (WMAP7) results, the newly revised $H(z)$ data, as well as a value of $θ_{BAO} (z=0.55) = (3.90 \pm 0.38)^{\circ}$ for the angular BAO scale. The constraint results for NGCG model are $ω_X = -1.0510_{-0.1685}^{+0.1563}(1σ)_{-0.2398}^{+0.2226}(2σ)$, $η= 1.0117_{-0.0502}^{+0.0469}(1σ)_{-0.0716}^{+0.0693}(2σ)$, and $Ω_X = 0.7297_{-0.0276}^{+0.0229}(1σ)_{-0.0402}^{+0.0329}(2σ)$, which give a rather stringent constraint. From the results, we can see a phantom model is slightly favored and the probability that energy transfers from dark matter to dark energy is a little larger than the inverse.

astro-ph.CO↗

arXiv2012

Constraints on f(R) cosmologies from strong gravitational lensing systems

f(R) gravity is thought to be an alternative to dark energy which can explain the acceleration of the universe. It has been tested by different observations including type Ia supernovae (SNIa), the cosmic microwave background (CMB), the baryon acoustic oscillations (BAO) and so on. In this Letter, we use the Hubble constant independent ratio between two angular diameter distances $D=D_{ls}/D_s$ to constrain f(R) model in Palatini approach $f(R)=R-αH^2_0(-\frac{R}{H^2_0})^β$. These data are from various large systematic lensing surveys and lensing by galaxy clusters combined with X-ray observations. We also combine the lensing data with CMB and BAO, which gives a stringent constraint. The best-fit results are $(α,β)=(-1.50,0.696)$ or $(Ω_m,β)=(0.0734,0.696)$ using lensing data only. When combined with CMB and BAO, the best-fit results are $(α,β)=(-3.75,0.0651)$ or $(Ω_m,β)=(0.286,0.0651)$. If we further fix $β=0$ (corresponding to $Λ$CDM), the best-fit value for $α$ is $α$=$-4.84_{-0.68}^{+0.91}(1σ)_{-0.98}^{+1.63}(2σ)$ for the lensing analysis and $α$=$-4.35_{-0.16}^{+0.18}(1σ)_{-0.25}^{+0.3}(2σ)$ for the combined data, respectively. Our results show that $Λ$CDM model is within 1$σ$ range.

astro-ph.CO↗

arXiv2012

Observational constraints on unified dark matter including Hubble parameter data

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 $P_X= p_0 +αρ_X$. 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: $Ω_Λ$=$0.719_{-0.0305}^{+0.0264}(1σ)_{-0.0458}^{+0.0380}(2σ)$, $α$=$1.72_{-4.79}^{+3.92}(1σ)_{-7.30}^{+5.47}(2σ)(\times10^{-3})$, $Ω_bh^2$=$0.0226_{-0.0011}^{+0.0011}(1σ)_{-0.0015}^{+0.0016}(2σ)$. Moreover, when considering a non-flat universe, $Ω_Λ$=$0.722_{-0.0447}^{+0.0362}(1σ)_{-0.0634}^{+0.0479}(2σ)$, $α$=$0.242_{-0.775}^{+0.787}(1σ)_{-1.03}^{+1.10}(2σ)(\times10^{-2})$, $Ω_bh^2$=$0.0227_{-0.0014}^{+0.0015}(1σ)_{-0.0018}^{+0.0021}(2σ)$, $Ω_k$=$-0.194_{-1.85}^{+2.02}(1σ)_{-2.57}^{+2.75}(2σ)(\times10^{-2})$. 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.

astro-ph.CO↗