Type Ia Supernovae Data Research Articles

THE ΛCDM GROWTH RATE OF STRUCTURE REVISITED

We re-examine the growth index of the concordance Λ cosmology in the light of the latest 6dF and WiggleZ data. In particular, we investigate five different models for the growth index γ, by comparing their cosmological evolution using observational data of the growth rate of structure formation at different redshifts. Performing a joint likelihood analysis of the recent supernovae type Ia data, the Cosmic Microwave Background shift parameter, Baryonic Acoustic Oscillations and the growth rate data, we determine the free parameters of the γ(z) parametrizations and we statistically quantify their ability to represent the observations. We find that the addition of the 6dF and WiggleZ growth data in the likelihood analysis improves significantly the statistical results. As an example, considering a constant growth index we find Ωm0 = 0.273 ± 0.011 and [Formula: see text].

Holographic Λ(t)CDM model in a non-flat universe

The holographic Λ(t)CDM model in a non-flat universe is studied in this paper. In this model, to keep the form of the stress-energy of the vacuum required by general covariance, the holographic vacuum is enforced to exchange energy with dark matter. It is demonstrated that for the holographic model the best choice for the IR cutoff of the effective quantum field theory is the event horizon size of the universe. We derive the evolution equations of the holographic Λ(t)CDM model in a non-flat universe. We constrain the model by using the current observational data, including the 557 Union2 type Ia supernovae data, the cosmic microwave background anisotropy data from the 7-yr WMAP, and the baryon acoustic oscillation data from the SDSS. Our fit results show that the holographic Λ(t)CDM model tends to favor a spatially closed universe (the best-fit value of Ω k0 is −0.042), and the 95 % confidence level range for the spatial curvature is −0.101<Ω k0<0.040. We show that the interaction between the holographic vacuum and dark matter induces an energy flow of which the direction is first from vacuum to dark matter and then from dark matter to vacuum. Thus, the holographic Λ(t)CDM model is just a time-varying vacuum energy scenario in which the interaction between vacuum and dark matter changes sign during the expansion of the universe.

RECONSTRUCTING THE HISTORY OF ENERGY CONDITION VIOLATION FROM OBSERVATIONAL DATA

We study the likelihood of energy condition violations in the history of the Universe. Our method is based on a set of functions that characterize energy condition violation. FLRW cosmological models are built around these "indication functions". By computing the Fisher matrix of model parameters using type Ia supernova and Hubble parameter data, we extract the principal modes of these functions' redshift evolution. These modes allow us to obtain general reconstructions of energy condition violation history independent of the dark energy model. We find that the data suggest a history of strong energy condition violation, but the null and dominant energy conditions are likely to be fulfilled. Implications for dark energy models are discussed.

Constraining dynamical dark energy with a divergence-free parametrization in the presence of spatial curvature and massive neutrinos

In this Letter, we report the results of constraining the dynamical dark energy with a divergence-free parameterization, w(z)=w0+wa(ln(2+z)1+z−ln2), in the presence of spatial curvature and massive neutrinos, with the 7-yr WMAP temperature and polarization data, the power spectrum of LRGs derived from SDSS DR7, the Type Ia supernova data from Union2 sample, and the new measurements of H0 from HST, by using a MCMC global fit method. Our focus is on the determinations of the spatial curvature, Ωk, and the total mass of neutrinos, ∑mν, in such a dynamical dark energy scenario, and the influence of these factors to the constraints on the dark energy parameters, w0 and wa. We show that Ωk and ∑mν can be well constrained in this model; the 95% CL limits are: −0.0153<Ωk<0.0167 and ∑mν<0.56eV. Comparing to the case in a flat universe, we find that the error in w0 is amplified by 25.51%, and the error in wa is amplified by 0.14%; comparing to the case with a zero neutrino mass, we find that the error in w0 is amplified by 12.24%, and the error in wa is amplified by 1.63%.

Combined cosmological and solar system constraints on chameleon mechanism

The chameleon mechanism appearing in the massive tensor-scalar theory of gravity can effectively reduce locally the nonminimal coupling between the scalar field and matter. This mechanism is invoked to reconcile large-scale departures from general relativity, supposedly accounting for cosmic acceleration, to small-scale stringent constraints on general relativity. In this paper, we carefully investigate this framework on cosmological and solar system scales to derive combined constraints on model parameters, notably by performing a nonambiguous derivation of observables like luminosity distance and local post-Newtonian parameters. The likelihood analysis of type Ia supernovae data and of an admissible domain for the parametrized-post-Newtonian parameters clearly demonstrates that the chameleon mechanism cannot occur in the same region of parameter space as the one necessary to account for cosmic acceleration with the assumed Ratra-Peebles potential and exponential coupling function.

Constraining the dark energy and smoothness parameter with type Ia supernovae and gamma-ray bursts

The existence of inhomogeneities in the observed Universe modifies the distance-redshift relations thereby affecting the results of cosmological tests in comparison to the ones derived assuming spatially uniform models. By modeling the inhomogeneities through a Zeldovich-Kantowski-Dyer-Roeder (ZKDR) approach which is phenomenologically characterized by a smoothness parameter $\alpha$, we rediscuss the constraints on the cosmic parameters based on Supernovae type Ia and Gamma-Ray Bursts (GRBs) data. The present analysis is restricted to a flat $\Lambda$CDM model with the reasonable assumption that $\Lambda$ does not clump. A $\chi^{2}$-analysis using 557 SNe Ia data from the Union2 Compilation Data (Amanullah {\it et al.} 2010) constrains the pair of parameters ($\Omega_m, \alpha$) to $\Omega_m=0.27_{-0.03}^{+0.08}$($2\sigma$) and $\alpha \geq 0.25$. A similar analysis based only on 59 Hymnium GRBs (Wei 2010) constrains the matter density parameter to be $\Omega_m= 0.35^{+0.62}_{-0.24}$ ($2\sigma$) while all values for the smoothness parameter are allowed. By performing a joint analysis, it is found that $\Omega_m = 0.27^{+0.06}_{-0.03}$ and $\alpha \geq 0.52$. As a general result, although considering that current GRB data alone cannot constrain the smoothness $\alpha$ parameter our analysis provides an interesting cosmological probe for dark energy even in the presence of inhomogeneities.

Dynamics and constraints of the dissipative Liouville cosmology

In this article we investigate the properties of the FLRW flat cosmological models in which the cosmic expansion of the Universe is affected by a dilaton dark energy (Liouville scenario). In particular, we perform a detailed study of these models in the light of the latest cosmological data, which serves to illustrate the phenomenological viability of the new dark energy paradigm as a serious alternative to the traditional scalar field approaches. By performing a joint likelihood analysis of the recent supernovae type Ia data (SNIa), the differential ages of passively evolving galaxies, and the baryonic acoustic oscillations (BAOs) traced by the Sloan Digital Sky Survey (SDSS), we put tight constraints on the main cosmological parameters. Furthermore, we study the linear matter fluctuation field of the above Liouville cosmological models. In this framework, we compare the observed growth rate of clustering measured from the optical galaxies with those predicted by the current Liouville models. Performing various statistical tests we show that the Liouville cosmological model provides growth rates that match well with the observed growth rate. To further test the viability of the models under study, we use the Press–Schechter formalism to derive their expected redshift distribution of cluster-size halos that will be provided by future X-ray and Sunyaev–Zeldovich cluster surveys. We find that the Hubble flow differences between the Liouville and the LambdaCDM models provide a significantly different halo redshift distribution, suggesting that the models can be observationally distinguished.

Cosmological tests of sudden future singularities

We discuss combined constraints, coming from the cosmic microwave background shift parameter $\mathcal{R}$, baryon acoustic oscillations (BAO) distance parameter $\mathcal{A}$, and from the latest type Ia supernovae data, imposed on cosmological models which allow sudden future singularities of pressure. We show that due to their weakness such sudden singularities may happen in the very near future and that at present they can mimic standard dark energy models.

Perturbations for transient acceleration

According to the standard ΛCDM model, the accelerated expansion of the Universe will go on forever. Motivated by recent observational results, we explore the possibility of a finite phase of acceleration which asymptotically approaches another period of decelerated expansion. Extending an earlier study on a corresponding homogeneous and isotropic dynamics, in which interactions between dark matter and dark energy are crucial, the present paper alsoinvestigates the dynamics of the matter perturbations both on the Newtonian and General Relativistic (GR) levels andquantifies the potential relevance of perturbations of the dark-energy component.In the background, the model is tested against the Supernova type Ia (SNIa) data of the Constitution setand on the perturbative level against growth rate data, among them those of the WiggleZ survey, and the data of the 2dFGRS project.Our results indicate that a transient phase of accelerated expansion is not excluded by current observations.

Einstein-aether theory as an alternative to dark energy model?

In the generalized Einstein-aether theories by taking a special form of the Lagrangian density of aether field, the possibility of Einstein-aether theory as an alternative to dark energy model is discussed in detail, that is, taking a special aether field as a dark energy candidate. We compute the joint statistic constraints on this special modelʼs parameters by using the recent type Ia supernovae (SNe Ia) data, the Cosmic Microwave Background (CMB) shift parameter data, and the Baryonic Acoustic Oscillations (BAOs) data traced by the Sloan Digital Sky Survey (SDSS). Furthermore, we analyze other constrains from the Observational Hubble parameter Data (OHD). The comparison with the standard cosmological model (cosmological constant Λ Cold Dark Matter (ΛCDM) model) is clearly shown with new features; also we comment on an interesting relation between the coupling constant M in this model and the possible existence of a special accelerating scale in the MOdified Newtonian Dynamics (MOND) model initially given by Milgrom with the hope for interpreting the galaxy rotation curves without introducing mysterious dark matter.

From cosmic deceleration to acceleration: new constraints from SN Ia and BAO/CMB

We use type Ia supernovae (SN Ia) data in combination with recent baryonic acoustic oscillations (BAO) and cosmic microwave background (CMB) observations to constrain a kink-like parametrization of the deceleration parameter (q). This q-parametrization can be written in terms of the initial (qi) and present (q0) values of the deceleration parameter, the redshift of the cosmic transition from deceleration to acceleration (zt) and the redshift width of such transition (τ). By assuming a flat space geometry, qi = 1/2 and adopting a likelihood approach to deal with the SN Ia data we obtain, at the 68% confidence level (C.L.), that: zt = 0.56+0.13−0.10, τ = 0.47+0.16−0.20 and q0 = −0.31+0.11−0.11 when we combine BAO/CMB observations with SN Ia data processed with the MLCS2k2 light-curve fitter. When in this combination we use the SALT2 fitter we get instead, at the same C.L.: zt = 0.64+0.13−0.07, τ = 0.36+0.11−0.17 and q0 = −0.53+0.17−0.13. Our results indicate, with a quite general and model independent approach, that MLCS2k2 favors Dvali-Gabadadze-Porrati-like cosmological models, while SALT2 favors ΛCDM-like ones. Progress in determining the transition redshift and/or the present value of the deceleration parameter depends crucially on solving the issue of the difference obtained when using these two light-curve fitters.

Holographic Ricci dark energy: interacting model and cosmological constraints

We extend the holographic Ricci dark energy model to include some direct, non-gravitational interaction between dark energy and dark matter. We consider three phenomenological forms for the interaction term $Q$ in the model, namely, $Q$ is taken proportional to the Hubble expansion rate and the energy densities of dark sectors (taken to be $\rho_{\rm de}$, $\rho_{\rm m}$, and $\rho_{\rm de}+\rho_{\rm m}$, respectively). We obtain a uniform analytical solution to the three interacting models. Furthermore, we constrain the models by using the latest observational data, including the 557 Union2 type Ia supernovae data, the cosmic microwave background anisotropy data from the 7-yr WMAP, and the baryon acoustic oscillation data from the SDSS. We show that in the interacting models of the holographic Ricci dark energy, a more reasonable value of $\Omega_{\rm m0}$ will be obtained, and the observations favor a rather strong coupling between dark energy and dark matter.

A Specific Case of Generalized Einstein-aether Theories

With the dark energy phenomena explored over a decade, in this present work we discuss a specific case of the generalized Einstein-aether theories, in which the modified Friedmann equation is similar to that in the Dvali—Gabadadze—Porrati (DGP) brane world model. We compute the joint statistic constraints on model parameters in this specific case by using the recent type Ia supernovae (SNe Ia) data, the cosmic microwave background (CMB) shift parameter data, and the baryonic acoustic oscillations (BAOs) data traced by the Sloan Digital Sky Survey (SDSS). Furthermore, we analyze other constrains from the observational Hubble parameter data (OHD). The comparison with the standard cosmological model (cosmological constant Λ cold dark matter (ΛCDM) model) is clearly shown; also we comment on the interesting relation between the coupling constant M in this model and the special accelerate scale in the modified Newtonian dynamics (MOND) model initially given by Milgrom with the hope for interpreting the galaxy rotation curves without introducing mysterious dark matter.

Testing the cosmic distance duality with X-ray gas mass fraction and supernovae data

Abstract In this Letter, we discuss a new cosmological-model-independent test for the cosmic distance duality relation (CDDR), η=DL(L)(1 +z)−2/DA(z) = 1, where DA(z) and DL(z) are the angular diameter and luminosity distances, respectively. Using the general expression for X-ray gas mass fraction (fgas) of galaxy clusters, fgas∝DLDA1/2, we show that fgas observations jointly with Type Ia supernovae (SNe Ia) data furnish a validity test for the CDDR. To perform our analysis, we use 38 fgas measurements recently studied by two groups considering different assumptions to describe the clusters and two subsamples of SNe Ia distance luminosity extracted from the Union2 compilation. In our test, we consider the η parameter as a function of the redshift parametrized by two different functional forms. It is found that the La Roque et al. sample is in perfect agreement with the duality relation (η= 1), whereas the Ettori et al. sample presents a significant conflict.

THE EFFECT OF DIFFERENT OBSERVATIONAL DATA IN CONSTRAINING COSMOLOGICAL PARAMETERS

We use the SNLS3 compilation of 472 type Ia supernova data, the baryon acoustic oscillation measurement of distance, and the cosmic microwave background radiation data from the seven year Wilkinson Microwave Anisotropy Probe to study the effect of their different combinations on the fittings of cosmological parameters. Neither BAO nor WMAP7 data alone gives good constraint on the equation of state parameter of dark energy, but both WMAP7 data and BAO data help type Ia supernova data break the degeneracies among the model parameters, hence tighten the constraint on the variation of equation of state parameter wa, and WMAP7 data does the job a little better. Although BAO and WMAP7 data provide reasonably good constraints on Ωm and Ωk, it is not able to constrain the dynamics of dark energy, we need SNe Ia data to probe the property of dark energy, especially the variation of the equation of state parameter of dark energy. For the SNLS SNe Ia data, the nuisance parameters α and β are consistent for all different combinations of the above data. Their impacts on the fittings of cosmological parameters are minimal. ΛCDM model is consistent with current observational data.

Constraining thawing quintessence

We look at observational constraints on the thawing class of scalar field models proposed to explain the late time acceleration of the universe. Using the recently introduced `Statefinder Hierarchy', we compare these thawing class of models with other widely studied dark energy (and modified gravity) models to check the underlying parameter degeneracies. We put constraints on the deviations of these thawing models from the canonical \Lambda CDM model using a large class of observational data, e.g, the Supernova Type Ia data, the BAO data, the CMB data and data from the measurements of the Hubble parameter using red-envelope galaxies. We also forecast constraints using a simulated dataset for the future JDEM SNe survey. Our study shows that, although with current data it is difficult to distinguish different thawing models from \Lambda CDM, a future JDEM like mission would be able tell apart thawing models from \Lambda CDM for currently acceptable values of \Omega_{m0}

χ2versus median statistics in supernova type Ia data analysis

In this paper we compare the performances of the chi-square and median likelihood analysis in the determination of cosmological constraints using type Ia supernovae data. We perform a statistical analysis using the 307 supernovae of the Union 2 compilation of the Supernova Cosmology Project and find that the chi-square statistical analysis yields tighter cosmological constraints than the median statistic if only supernovae data is taken into account. We also show that when additional measurements from the Cosmic Microwave Background and Baryonic Acoustic Oscillations are considered, the combined cosmological constraints are not strongly dependent on whether one applies the chi-square statistic or the median statistic to the supernovae data. This indicates that, when complementary information from other cosmological probes is taken into account, the performances of the chi-square and median statistics are very similar, demonstrating the robustness of the statistical analysis.

Testing the distance-duality relation with a combination of cosmological distance observations

We propose an accurate test of the distance-duality (DD) relation, η = DL(z)(1 + z)−2/DA(z) = 1 (where DL and DA are the luminosity distances and angular diameter distances, respectively), with a combination of cosmological observational data of Type Ia Supernovae (SNe Ia) from the Union2 set and the galaxy cluster sample under an assumption of the spherical model. In order to avoid bias brought on by redshift non-coincidence between observational data and to consider redshift error bars of both clusters and SNe Ia in the analysis, we carefully choose the SNe Ia points which have the minimum acceptable redshift difference of the galaxy cluster sample (|Δz|min = σz,SN + σz,cluster). By assuming η to be a constant and defined as functions of the redshift parameterized by six different expressions, we find that there exists no observable evidence for variations in the DD relation based on the collected data, since related statistical tests are well satisfied within the 1σ confidence level for most cases. Further, considering different values of Δz as constraints, we also find that the choice of Δz may play an important role in this model-independent test of the DD relation for the spherical sample of galaxy clusters.

Generalized Lemaître-Tolman-Bondi model with inhomogeneous isotropic dark energy: Observational constraints

We consider on-center and off-center observers in an inhomogeneous, spherically symmetric, isocurvature (flat) concentration of dark energy with a typical size of a few Gpc. Such a concentration could be produced e.g. by a recently formed global monopole with core size that approaches the Hubble scale. In this case we would have what may be called ``topological quintessence'' in analogy with the well-known topological inflation. We show that the minimum comoving radius ${r}_{0\mathrm{min}}$ of such a dark energy inhomogeneity that is consistent with the Union2 type Ia supernovae data at the $3\ensuremath{\sigma}$ level is ${r}_{0\mathrm{min}}\ensuremath{\simeq}1.8\text{ }\text{ }\mathrm{Gpc}$. As expected, the best-fit fractional dark energy density at the center, ${\ensuremath{\Omega}}_{X,\mathrm{in}}$, approaches the corresponding $\ensuremath{\Lambda}\mathrm{CDM}$ value ${\ensuremath{\Omega}}_{X,\mathrm{in}}=0.73$ for large enough values of the inhomogeneity radius ${r}_{0}$ (${r}_{0}&gt;4\text{ }\text{ }\mathrm{Gpc}$). Using the Union2 data, we show that the maximum allowed shift ${r}_{\mathrm{obs}\mathrm{\text{\ensuremath{-}}}\mathrm{max}}$ of the observer from the center of the inhomogeneity is about $0.7{r}_{0}$, which respects the Copernican principle. The model naturally predicts the existence of a preferred axis and alignment of the low CMB multipoles. However, the constraints on ${r}_{\mathrm{obs}\mathrm{\text{\ensuremath{-}}}\mathrm{max}}$ coming from the magnitude of the CMB dipole remain a severe challenge to the Copernican principle and lead to ${r}_{\mathrm{obs}\mathrm{\text{\ensuremath{-}}}\mathrm{max}}&lt;110\text{ }\text{ }\mathrm{Mpc}$, even for an inhomogeneity radius as large as ${r}_{0}=7\text{ }\text{ }\mathrm{Gpc}$.

Analysis of recent type Ia supernova data based on evolving dark energy models

We study characters of recent type Ia supernova (SNIa) data using evolving dark energy models with changing equation of state parameter w. We consider sudden-jump approximation of w for some chosen redshift spans with double transitions, and constrain these models based on Markov Chain Monte Carlo (MCMC) method using the SNIa data (Constitution, Union, Union2) together with baryon acoustic oscillation A parameter and cosmic microwave background shift parameter in a flat background. In the double-transition model the Constitution data shows deviation outside 1 sigma from LCDM model at low (z < 0.2) and middle (0.2 < z < 0.4) redshift bins whereas no such deviations are noticeable in the Union and Union2 data. By analyzing the Union members in the Constitution set, however, we show that the same difference is actually due to different calibration of the same Union sample in the Constitution set, and is not due to new data added in the Constitution set. All detected deviations are within 2 sigma from the LCDM world model. From the LCDM mock data analysis, we quantify biases in the dark energy equation of state parameters induced by insufficient data with inhomogeneous distribution of data points in the redshift space and distance modulus errors. We demonstrate that location of peak in the distribution of arithmetic means (computed from the MCMC chain for each mock data) behaves as an unbiased estimator for the average bias, which is valid even for non-symmetric likelihood distributions.