Nan Liang

Peking University, Peping, Beijing, China

Are you Nan Liang?

Claim your profile

Publications (13)36.14 Total impact

  • Source
    Shuo Cao, Nan Liang
    [Show abstract] [Hide abstract]
    ABSTRACT: In order to test if there is energy transfer between dark energy and dark matter, we investigate cosmological constraints on two forms of nontrivial interaction between the dark matter sector and the sector responsible for the acceleration of the universe, in light of the newly revised observations including OHD, CMB, BAO and SNe Ia. More precisely, we find the same tendencies for both phenomenological forms of the interaction term $Q=3\gamma H\rho$, i.e., the parameter $\gamma$ to be a small number, $|\gamma|\approx 10^{-2}$. However, concerning the sign of the interaction parameter, we observe that $\gamma>0$ when the interaction between dark sectors is proportional to the energy density of dust matter, whereas the negative coupling ($\gamma<0$) is preferred by observations when the interaction term is proportional to dark energy density. We further discuss two possible explanations to this incompatibility and apply a quantitative criteria to judge the severity of the coincidence problem. Results suggest that the $\gamma_m$IDE model with a positive coupling may alleviate the coincidence problem, since its coincidence index $C$ is smaller than that for the $\gamma_d$IDE model, the interacting quintessence and phantom models by four orders of magnitude.
    International Journal of Modern Physics D 05/2011; · 1.03 Impact Factor
  • Source
    Shuo Cao, Nan Liang
    [Show abstract] [Hide abstract]
    ABSTRACT: In this paper, we propose an accurate test of the distance-duality (DD) relation, $\eta=D_{L}(z)(1+z)^{-2}/D_{A}(z)=1$ (where $D_{L}$ and $D_{A}$ are the luminosity distances and angular diameter distances, respectively), with a combination of cosmological observational data of Type Ia Supernave (SNe Ia) from Union2 set and the galaxy cluster sample under an assumption of spherical model. In order to avoid bias brought by redshift incoincidence between observational data and to consider redshift error bars of both clusters and SNe Ia in analysis, we carefully choose the SNe Ia points which have the minimum acceptable redshift difference of the galaxy cluster sample ($|\Delta z|_{\rm min} =\sigma_{z, \rm SN}+\sigma_{z, \rm cluster}$). By assuming $\eta$ a constant and functions of the redshift parameterized by six different expressions, we find that there exists no conceivable evidence for variations in the DD relation concerning with observational data, since it is well satisfied within $1\sigma$ confidence level for most cases. Further considering different values of $\Delta z$ in constraining, we also find that the choosing of $\Delta z$ may play an important role in this model-independent test of the distance-duality relation for the spherical sample of galaxy clusters.
    Research in Astronomy and Astrophysics 04/2011; 11(10). · 1.35 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: 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 $\eta \equiv {D_L}{(1+z)}^{-2}/{D_A}=1$ is satisfied within $2\sigma$ confidence level for various parameterizations of $\eta(z)$, which are more stringent than previous testing results without considering redshift bias.
    Monthly Notices of the Royal Astronomical Society 04/2011; · 5.52 Impact Factor
  • Source
    Shuo Cao, Nan Liang, Zong-Hong Zhu
    [Show abstract] [Hide abstract]
    ABSTRACT: In order to test the possible interaction between dark energy and dark matter, we investigate observational constraints on a phenomenological scenario, in which the ratio between the dark energy and matter densities is proportional to the power law case of the scale factor, $r\equiv (\rho_X/\rho_m)\propto a^{\xi}$. By using the Markov chain Monte Carlo method, we constrain the phenomenological interacting dark energy model with the newly revised $H(z)$ data, as well as the cosmic microwave background (CMB) observation from the 7-year Wilkinson Microwave Anisotropy Probe (WMAP7) results, the baryonic acoustic oscillation (BAO) observation from the spectroscopic Sloan Digital Sky Survey (SDSS) data release 7 (DR7) galaxy sample and the type Ia supernovae (SNe Ia) from Union2 set. The best-fit values of the model parameters are $\Omega_{m0}=0.27_{-0.02}^{+0.02}(1\sigma)_{-0.03}^{+0.04}(2\sigma)$, $\xi=3.15_{-0.50}^{+0.48}(1\sigma)_{-0.71}^{+0.72}(2\sigma)$, and $w_X=-1.05_{-0.14}^{+0.15}(1\sigma)_{-0.21}^{+0.21}(2\sigma)$, which are more stringent than previous results. These results show that the standard $\Lambda$CDM model without any interaction remains a good fit to the recent observational data; however, the interaction that the energy transferring from dark matter to dark energy is slightly favored over the interaction from dark energy to dark matter. It is also shown that the $H(z)$ data can give more stringent constraints on the phenomenological interacting scenario when combined to CMB and BAO observations, and the confidence regions of $H(z)$+BAO+CMB, SNe+BAO+CMB, and $H(z)$+SNe+BAO+CMB combinations are consistent with each other.
    Monthly Notices of the Royal Astronomical Society 12/2010; · 5.52 Impact Factor
  • Source
    Shuo Cao, Zong-Hong Zhu, Nan Liang
    [Show abstract] [Hide abstract]
    ABSTRACT: The interacting dark matter (IDM) scenario allows for the acceleration of the Universe without Dark Energy. We constrain the IDM model by using the newly revised observational data including $H(z)$ data and Union2 SNe Ia via the Markov chain Monte Carlo method. When mimicking the $\Lambda$CDM model, we obtain a more stringent upper limit to the effective annihilation term at $\kappa C_1\approx 10^{-3.4}\rm{Gyr}^{-1}$, and a tighter lower limit to the relevant mass of Dark Matter particles at $M_x\approx 10^{-8.6}\rm{Gev}$. When mimicking the $w$CDM model, we find that the effective equation of state of IDM is consistent with the concordance $\Lambda$CDM model and appears to be most consistent with the effective phantom model with a constant EoS for which $w<-1$.
    Astronomy and Astrophysics 11/2010; · 5.08 Impact Factor
  • Source
    Nan Liang, Zong-Hong Zhu
    [Show abstract] [Hide abstract]
    ABSTRACT: We investigate observational constraints on the Dvali, Gabadadze and Porrati (DGP) model with Gamma-ray bursts (GRBs) at high redshift obtained directly from the Union2 Type Ia supernovae data (SNe Ia) set. With the cosmology-independent GRBs, the Union2 set, as well as the cosmic microwave background (CMB) observations from the WMAP7 result, the baryon acoustic oscillation, the baryon mass fraction in clusters and the observed $H(z)$ data, we obtain that the best-fit values of the DGP model are ${\Omega_{M0}, \Omega_{rc}} =\{0.235_{-0.014}^{+0.015},0.138_{-0.048}^{+0.051}\}$, which favor a flat universe; and the transition redshift of the DGP model is $z_T=0.67_{-0.04}^{+0.03}$. These results lead to more stringent constraints than the previous results for the DGP model.
    Research in Astronomy and Astrophysics 10/2010; 11(5). · 1.35 Impact Factor
  • Source
    Nan Liang, Lixin Xu, Zong-Hong Zhu
    [Show abstract] [Hide abstract]
    ABSTRACT: We investigate observational constraints on the generalized Chaplygin gas (GCG) model including the gamma-ray bursts (GRBs) at high redshift obtained directly from the Union2 type Ia supernovae (SNe Ia) set. By using the Markov Chain Monte Carlo method, we constrain the GCG model with the cosmology-independent GRBs, as well as the Union2 set, the cosmic microwave background (CMB) observation from the Wilkinson Microwave Anisotropy Probe (WMAP7) result, and the baryonic acoustic oscillation (BAO) observation from the spectroscopic Sloan Digital Sky Survey (SDSS) data release 7 (DR7) galaxy sample. The best-fit values of the GCG model parameters are $A_S$=$0.7475_{-0.0539}^{+0.0556}(1\sigma)_{-0.0816}^{+0.0794}(2\sigma)$, $\alpha$=$-0.0256_{-0.1326}^{+0.1760}(1\sigma)_{-0.1907}^{+0.2730}(2\sigma)$, and the effective matter density $\Omega_{m}=0.2629_{-0.0153}^{+0.0155}(1\sigma)_{-0.0223}^{+0.0236}(2\sigma)$, which are more stringent than the previous results for constraining on GCG model parameters.
    Astronomy and Astrophysics 09/2010; · 5.08 Impact Factor
  • Source
    Nan Liang, Puxun Wu, Zong-Hong Zhu
    [Show abstract] [Hide abstract]
    ABSTRACT: In this paper, we constrain the Cardassian expansion models from the latest observations including the updated Gamma-ray bursts (GRBs), which calibrated cosmology-independently from the Union2 compilation of type Ia supernovae (SNe Ia). By combining the GRB data to the joint observations with the Union2 SNe Ia set, along with the Cosmic Microwave Background radiation observation from the seven-year Wilkinson Microwave Anisotropy Probe result, the baryonic acoustic oscillation observation from the spectroscopic Sloan Digital Sky Survey Data Release galaxy sample, we find significant constraints on model parameters of the original Cardassian model $\Omega_{{\rm M0}}=0.282_{-0.014}^{+0.015}$, $n= 0.03_{-0.05}^{+0.05}$; and $n= -0.16_{-3.26}^{+0.25}$, $\beta=0.76_{-0.58}^{+0.34}$ of the modified polytropic Cardassian model, which are consistent with the $\Lambda$CDM model in 1-$\sigma$ confidence region. From the reconstruction of the deceleration parameter $q(z)$ in Cardassian models, we obtain the transition redshift $z_{\rm T}=0.73\pm{0.04}$ for the original Cardassian model, and $z_{\rm\rm T}=0.68\pm{0.04}$ for the modified polytropic Cardassian model.
    Research in Astronomy and Astrophysics 06/2010; · 1.35 Impact Factor
  • Source
    He Gao, Nan Liang, Zong-Hong Zhu
    [Show abstract] [Hide abstract]
    ABSTRACT: For the use of Gamma-Ray Bursts (GRBs) to probe cosmology in a cosmology-independent way, a new method has been proposed to obtain luminosity distances of GRBs by interpolating directly from the Hubble diagram of SNe Ia, and then calibrating GRB relations at high redshift. In this paper, following the basic assumption in the interpolation method that objects at the same redshift should have the same luminosity distance, we propose another approach to calibrate GRB luminosity relations with cosmographic fitting directly from SN Ia data. In cosmography, there is a well-known fitting formula which can reflect the Hubble relation between luminosity distance and redshift with cosmographic parameters which can be fitted from observation data. Using the Cosmographic fitting results from the Union set of SNe Ia, we calibrate five GRB relations using GRB sample at $z\leq1.4$ and deduce distance moduli of GRBs at $1.4< z \leq 6.6$ by generalizing above calibrated relations at high redshift. Finally, we constrain the dark energy parameterization models of the Chevallier-Polarski-Linder (CPL) model, the Jassal-Bagla-Padmanabhan (JBP) model and the Alam model with GRB data at high redshift, as well as with the Cosmic Microwave Background radiation (CMB) and the baryonic acoustic oscillation (BAO) observations, and we find the $\Lambda$CDM model is consistent with the current data in 1-$\sigma$ confidence region.
    International Journal of Modern Physics D 03/2010; · 1.03 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: We investigate the cosmological evolution of a two-field model of dark energy, where one is a dilaton field with canonical kinetic energy and the other is a phantom field with a negative kinetic energy term. Phase-plane analysis shows that the ``phantom"-dominated scaling solution is the stable late-time attractor of this type of model. We find that during the evolution of the universe, the equation of state w changes from w > -1 to w < -1, which is consistent with recent observations.
    Chinese Physics Letters 01/2009; 26(6). · 0.92 Impact Factor
  • Source
    Nan Liang, Shuang Nan Zhang
    [Show abstract] [Hide abstract]
    ABSTRACT: This report is an update and extension of our paper accepted for publication in ApJ (arXiv:0802.4262). Since objects at the same redshift should have the same luminosity distance and the distance moduli of type Ia supernovae (SNe Ia) obtained directly from observations are completely cosmology independent, we obtain the distance modulus of a gamma-ray burst (GRB) at a given redshift by interpolating or iterating from the Hubble diagram of SNe Ia. Then we calibrate five GRB relations without assuming a particular cosmological model, from different regression methods, and construct the GRB Hubble diagram to constrain cosmological parameters. Based upon these relations we list the cosmology-independent distance moduli of 42 GRBs between redshift of 1.44 and 6.60, with the 1-$\sigma$ uncertainties of 1-3%. Comment: 6 pages, 2 figures, 3 tables. To appear in the proceedings of "2008 Nanjing GRB conference", Nanjing, 23-27 June 2008
    08/2008;
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: An important concern in the application of gamma-ray bursts (GRBs) to cosmology is that the calibration of GRB luminosity/energy relations depends on the cosmological model, due to the lack of a sufficient low-redshift GRB sample. In this paper, we present a new method to calibrate GRB relations in a cosmology-independent way. Since objects at the same redshift should have the same luminosity distance and since the distance moduli of Type Ia supernovae (SNe Ia) obtained directly from observations are completely cosmology independent, we obtain the distance modulus of a GRB at a given redshift by interpolating from the Hubble diagram of SNe Ia. Then we calibrate seven GRB relations without assuming a particular cosmological model and construct a GRB Hubble diagram to constrain cosmological parameters. From the 42 GRBs at $1.4<z\le6.6$, we obtain $\Omega_{\rm M}=0.25_{-0.05}^{+0.04}$, $\Omega_{\Lambda}=0.75_{-0.04}^{+0.05}$ for the flat $\Lambda$CDM model, and for the dark energy model with a constant equation of state $w_0=-1.05_{-0.40}^{+0.27}$, which is consistent with the concordance model in a 1-$\sigma$ confidence region. Comment: 7 pages, 3 figures, 1 table, now matches the editorially revised version; accepted for publication in ApJ (vol 685);
    The Astrophysical Journal 02/2008; · 6.73 Impact Factor
  • Source
    TaiShan Wang, Nan Liang
    [Show abstract] [Hide abstract]
    ABSTRACT: Constraints on the original Cardassian model and the modified polytropic Cardassian model are examined from the recently derived 42 gamma-ray bursts (GRBs) data calibrated with the method that can avoid the circularity problem. The results show that GRBs can be an optional observation to constrain the Cardassian models. Combining the GRBs data with the newly derived size of baryonic acoustic oscillation peak from the Sloan Digital Sky Survey (SDSS), and the position of the first acoustic peak of the Cosmic Microwave Background radiation (CMB) from Wilkinson Microwave Anisotropy Probe (WMAP), we find Ω mo = 0.27−0.02+0.02, n = 0.06−0.08+0.07 (1σ for the original Cardassian model, and Ω mo = 0.27−0.02+0.03, n = −0.09−1.91+0.23 β = 0.82−0.62+2.10 (1 σ) for the modified polytropic Cardassian model. KeywordsCardassian-Gamma ray burst-Cosmic Microwave Background-baryonic acoustic oscillation
    Science China: Physics, Mechanics and Astronomy 53(9):1720-1725. · 1.17 Impact Factor