Type Ia Supernovae Data Research Articles

How strong is the evidence for accelerated expansion?

We test the present expansion of the universe using supernova type Ia data without makingany assumptions about the matter and energy content of the universe or about theparametrization of the deceleration parameter. We assume the cosmological principle toapply in a strict sense. The result strongly depends on the data set, the light curve fittingmethod and the calibration of the absolute magnitude used for the test, indicatingstrong systematic errors. Nevertheless, in a spatially flat universe there is at least5σ evidence for accelerationwhich drops to 1.8σ in an open universe.

RECONSTRUCTING GENERALIZED GHOST CONDENSATE MODEL WITH DYNAMICAL DARK ENERGY PARAMETRIZATIONS AND OBSERVATIONAL DATASETS

Observations of high-redshift supernovae indicate that the universe is accelerating at the present stage, and we refer to the cause for this cosmic acceleration as "dark energy". In particular, the analysis of current data of type Ia supernovae (SNIa), cosmic large-scale structure (LSS), and the cosmic microwave background (CMB) anisotropy implies that, with some possibility, the equation-of-state parameter of dark energy may cross the cosmological-constant boundary (w = -1) during the recent evolution stage. The model of "quintom" has been proposed to describe this w = -1 crossing behavior for dark energy. As a single-real-scalar-field model of dark energy, the generalized ghost condensate model provides us with a successful mechanism for realizing the quintom-like behavior. In this paper, we reconstruct the generalized ghost condensate model in the light of three forms of parametrization for dynamical dark energy, with the best-fit results of up-to-date observational data.

Constraining bouncing cosmology caused by the Casimir effect

We constrain the Friedmann-Robertson-Walker (FRW) model with a “radiation-like” contribution to the Friedmann equation against the astronomical data. We analyze the observational bounds on a (1 + z)4 term from type Ia supernovae (SNIa) data, Fanaroff-Riley type IIb (FRIIb) radio galaxy (RG) data, baryon oscillation peak and cosmic microwave background radiation (CMBR) observations. We argue that it is not possible to determine the energy densities of individual components scaling like radiation from a kinematic astronomical test. The bounds for the density parameter of the total radiation-like term can be obtained. We find different interpretations of the presence of a scaling-like radiation term: the FRW universe filled with a massless scalar field in a quantum regime (the Casimir effect), the FRW model in a semiclassical approximation of loop quantum gravity, the FRW model in the Randall-Sundrum scenario with dark radiation or a cosmological model with global rotation. In this paper, we mainly concentrate on the Casimir effect arising from quantum effects of a scalar field. This contribution can describe a decaying part of the cosmological constant. We discuss the back-reaction of gravity on the Casimir-type force which is a manifestation of the vacuum fluctuations of the quantum scalar field at low temperature. It is shown that, while the Casimir energy gives rise to the accelerating Universe, the cosmological constant term is still required. We argue that a small negative contribution of a radiation-like term can reconcile the tension between the observed primordial 4He and D abundances. Moreover, the presence of such a contribution can also remove the disagreement between the Hubble parameter H0 values obtained from the SNIa and Wilkinson Microwave Anisotropy Probe (WMAP) satellite data.

Extending the Redshift-Distance Relation in Cosmological General Relativity to Higher Redshifts

The redshift-distance modulus relation, the Hubble Diagram, derived from Cosmological General Relativity has been extended to arbitrarily large redshifts. Numerical methods were employed and a density function was found that results in a valid solution of the field equations at all redshifts. The extension has been compared to 302 type Ia supernova data as well as to 69 Gamma-ray burst data. The latter however do not not truly represent a `standard candle' as the derived distance modulii are not independent of the cosmology used. Nevertheless the analysis shows a good fit can be achieved without the need to assume the existence of dark matter. The Carmelian theory is also shown to describe a universe that is always spatially flat. This results from the underlying assumption of the energy density of a cosmological constant $\Omega_{\Lambda} = 1$, the result of vacuum energy. The curvature of the universe is described by a \textit{spacevelocity} metric where the energy content of the curvature at any epoch is $\Omega_K = \Omega_{\Lambda} - \Omega = 1-\Omega$, where $\Omega$ is the matter density of the universe. Hence the total density is always $\Omega_K + \Omega = 1$

Bulk viscous cosmology

We propose a scenario in which the dark components of the Universe are manifestations of a single bulk viscous fluid. Using dynamical system methods, a qualitative study of the homogeneous, isotropic background scenario is performed in order to determine the phase space of all possible solutions. The specific model which we investigate shares similarities with a generalized Chaplygin gas in the background but is characterized by nonadiabatic pressure perturbations. This model is tested against supernova type Ia and matter power spectrum data. Different from other unified descriptions of dark matter and dark energy, the matter power spectrum is well behaved, i.e., there are no instabilities or oscillations on small perturbation scales. The model is competitive in comparison with the currently most popular proposals for the description of the cosmological dark sector.

CONSTRAINTS ON SIMPLIFIED QUARTESSENCE COSMOLOGY FROM THE LATEST OBSERVATIONAL DATA

The simplified generalized Chaplygin gas (GCG) model as a candidate of UDME is studied in this paper. By using the latest 162 ESSENCE type Ia supernovae (Sne Ia ) data, 30 high red shift Sne Ia data and the distance ratio from z = 0.35 to z = 1089 (the red shift of decoupling), we obtain [Formula: see text] and [Formula: see text] at a 95.4% confidence level. In addition the deceleration parameter for this simplified GCG model is investigated, and we find that the universe, at a 1σ confidence level, enters the acceleration era at the red shift zq = 0~ 0.53 - 0.66 and possesses an acceleration -qz = 0~ 0.66 - 0.78 at present.

Monte‐Carlo simulation of a possible correlation between the estimated luminosity distances and internal extinctions of type Ia supernovae

AbstractThis paper describes a Monte Carlo simulation of type Ia supernova data. It was shown earlier that the data of SNe Ia might contain a possible correlation between the estimated luminosity distances and internal extinctions. This correlation was shown by different statistical investigations of the data. In order to remove observational biases (for example the effect of the detection limit of the observing instrument) and to test the reality of the effect found earlier we developed a simple routine which simulates extinction values, redshifts and absolute magnitudes for Ia supernovae. We pointed out that the correlation found earlier in the real data between the internal extinction and luminosity distance does not occur in the simulated sample. Furthermore, it became obvious that the detection limit of the observing devices used in supernova projects does not affect the far end of the redshift‐luminosity distance relationship of Ia supernovae. This result strengthens the earlier conclusions of the authors that SN Ia supernovae alone do not support the existence of dark energy. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Narrowing constraints with type Ia supernovae: converging on a cosmologicalconstant

We apply a parameterization-independent approach to fitting the dark energyequation-of-state (EOS). Utilizing the latest type Ia supernova data, combined withresults from the cosmic microwave background and baryon acoustic oscillations,we find that the dark energy is consistent with a cosmological constant. Weestablish independent estimates of the evolution of the dark energy EOS bydiagonalizing the covariance matrix. We find three independent constraints,which taken together imply that the equation of state is more negative than−0.2 at the 68% confidence level in the redshift range0<z<1.8, independent of the flat universe assumption. Our estimates argue against previous claimsof dark energy ‘metamorphosis’, where the EOS was found to be strongly varying at lowredshifts. Our results are inconsistent with extreme models of dynamical dark energy, both inthe form of ‘freezing’ models where the dark energy EOS begins with a value greater than−0.2 atz>1.2 and rolls toa value of −1 today, and ‘thawing’ models where the EOS is near−1 at high redshifts, but rapidly evolves to values greater than−0.85 atz<0.2. Finally, we propose a parameterization-independent figure of merit (FOM), to help assessthe ability of future surveys to constrain dark energy. While the more common FOMpresumes a specific dark energy parameterization with two parameters, we suggest abinning approach to evaluate dark energy constraints with a minimum number ofassumptions.

Constraint on cosmological model with matter creation using complementary astronomical observations

The universe with adiabatic matter creation is considered. It is thought that the negative pressure caused by matter creation can play the role of a dark energy component, and drive the accelerating expansion of the universe. Using the Type Ia supernovae (SNe Ia) data, the observational Hubble parameter data, the Cosmic Microwave Background (CMB) data and the Baryonic Acoustic Oscillation (BAO) data, we make constraints on the cosmological parameters, assuming a spatially flat universe. Our results show that the model with matter creation is consistent with the SNe Ia data, while the joint constraints of all these observational data disfavor this model. If the cosmological constant is taken into account, a traditional model without matter creation is favored by the joint observations.

Observation Constraints on the Simplified GCG Model

A simplified version of generalized Chaplygin gas (GCG) as a dark energymodel is studied. By using the latest 162 ESSENCE type Ia supernovae(Sne Ia) data, 30 high redshift Sne Ia data, the baryonic acousticoscillation peak from SDSS and the CMB data from WMAP3, a strongconstraint on this simplified GCG model is obtained. At the 95.4%confidence level we obtain 0.21⩽Ωm⩽0.31 and0.994⩽α⩽1.0 with the best fit Ωm = 0.25 andα = 1. This best fit scenario corresponds to an acceleratinguniverse with q0≃−0.65 and z≃0.81 (a redshift of cosmicphase transition from deceleration to acceleration).

The tension of cosmological magnetic fields as a contribution to dark energy

We propose that cosmological magnetic fields generated in regions of finite spatial dimensions may manifest themselves in the global dynamics of the Universe as “dark energy”. We test our model in the context of spatially flat cosmological models by assuming that the Universe contains non-relativistic matter , dark energy , and an extra fluid with that corresponds to the magnetic field. We place constraints on the main cosmological parameters of our model by combining the recent supernovae type Ia data and the differential ages of passively evolving galaxies. In particular, we find that the model which best reproduces the observational data when = 0.26 is one with 0.03, 7.68, 0.71 and -0.8.

Constraining a double component dark energy model using supernova type Ia data

A two-component fluid representing dark energy is studied. One of the components has a polytropic form, while the other has a barotropic form. Exact solutions are obtained and the cosmological parameters are constrained using supernova type Ia data. In general, an open universe is predicted. A big rip scenario is largely preferred, but the dispersion in the parameter space is very high. Hence, even if scenarios without future singularities can not be excluded with the allowed range of parameters, a phantom cosmology, with an open spatial section, is a general prediction of the model. For a wide range of the equation of state parameters there is an asymptotic de Sitter phase.

Constraints on the Generalized Chaplygin Gas Model from Recent Supernova Data and Baryonic Acoustic Oscillations

Constraints from the Gold sample Type Ia supernova (SN Ia) data, the Supernova Legacy Survey (SNLS) SN Ia data, and the size of the baryonic acoustic oscillation (BAO) peak found in the Sloan Digital Sky Survey (SDSS) on the generalized Chaplygin gas (GCG) model, proposed as a candidate for the unified dark matter-dark energy scenario (UDME), are examined in the cases of both a spatially flat and a spatially curved universe. Our results reveal that the GCG model is consistent with a flat universe up to the 68% confidence level, and the model parameters are within the allowed parameter ranges of the GCG as a candidate for UDME. Meanwhile, we find that in the flat case, both the Gold sample + SDSS BAO data and the SNLS sample + SDSS BAO data break the degeneracy of As and α and allow for the scenario of a cosmological constant plus dark matter (α = 0) at the 68% confidence level, although they rule out the standard Chaplygin gas model (α = 1) at the 99% confidence level. However, for the case without a flat prior, the SNLS SN Ia + SDSS BAO data do not break the degeneracy between As and α, and they allow for ΛCDM (α = 0) and the standard Chaplygin gas model (α = 1) at a 68% confidence level, while the Gold SN Ia + SDSS BAO break the degeneracy of As and α and rule out ΛCDM at a 68% confidence level and the standard Chaplygin gas model at a 99% confidence level.

Constraints on the unified dark energy–dark matter model from latest observationaldata

The generalized Chaplygin gas (GCG) is studied in this paper by usingthe latest observational data including 182 gold sample type Ia supernovae(Sne Ia) data, the ESSENCE Sne Ia data, the distance ratio fromz = 0.35 to 1089 (the redshift of decoupling), the cosmic microwave background shift parameter andthe Hubble parameter data. Our results rule out the standard Chaplygin gas model(α = 1) at the99.7% confidence level,but allow for the λCDM model (α = 0) at the68.3% confidence level.At a 95.4% confidencelevel, we obtain w = −0.74−0.09+0.10 and α = −0.14−0.19+0.30. In addition, we find that the phase transition from deceleration to acceleration occurs at redshiftzq = 0∼0.78−0.89 ata 1σ confidence level for the GCG model.

Observational Constraints on the UnifiedDark-Energy–Dark-Matter Model

We investigate the constraints on a generalized Chaplygin gas (GCG)model using the gold sample type-Ia supernovae (Sne Ia) data, thenew Supernova Legacy Survey (SNLS) Sne Ia data and the size ofbaryonic acoustic oscillation peak found in Sloan Digital Sky Survey(SDSS). In a spatially flat universe case we obtain, at a 95.4%confidence level, As = 0.76−0.07+0.07 andα = 0.028−0.238+0.322. Our results are consistent withthe ΛCDM model (α = 0), but rule out the standardChaplygin gas model (α = 1).

Dark energy parametrizations and the curvature of the universe

We investigate observational constraints on the curvature of the universe not restrictingourselves to a cosmological constant as dark energy, in particular allowing a darkenergy equation of state to evolve with time in several ways. We use type Iasupernovae (SNeIa) data from the latest gold data set which includes 182SNeIa, along with the cosmic microwave background shift parameter and thebaryon acoustic oscillation peak. We show quantitatively that the constraint onthe curvature of the universe depends on the dark energy model: some popularparametrizations give constraints closely around the flat universe at 5% level(2σ C.L.) whereas some parametrizations allow the universe to be as open as havingΩk ∼ 0.2.

Cosmology with a variable Chaplygin gas

We consider a new generalized Chaplygin gas model that includes the original Chaplygin gas model as a special case. In such a model the generalized Chaplygin gas evolves as from dust to quiescence or phantom. We show that the background evolution for the model is equivalent to that for a coupled dark energy model with dark matter. The constraints from the current type Ia supernova data favour a phantom-like Chaplygin gas model.

Crossingw=−1by a single scalar on a Dvali-Gabadadze-Porrati brane

Recent type Ia supernovae data seem to favor a dark energy model whose equation of state $w(z)$ crosses $\ensuremath{-}1$, which is a much more amazing problem than the acceleration of the universe. Either the case that $w(z)$ evolves from above $\ensuremath{-}1$ to below $\ensuremath{-}1$ or the case that $w(z)$ runs from below $\ensuremath{-}1$ to above $\ensuremath{-}1$, is consistent with present data. In this paper we show that it is possible to realize the crossing behaviors of both of the two cases by only a single scalar field in frame of Dvali-Gabadadze-Porrati braneworld. At the same time we prove that there does not exist scaling solution in a universe with dust.

A possible interrelation between the estimated luminosity distances and internal extinctions of type Ia supernovae

We studied the statistical properties of the luminosity distance and internal extinction data of type Ia supernovae in the lists published by Tonry et al. (2003) and Barris et al. (2004). After selecting the luminosity distance in an empty Universe as a reference level we divided the sample into low z < 0.25 and high z ≥ 0.25 parts. We further divided these subsamples by the median of the internal extinction. Performing sign tests using the standardized residuals between the estimated logarithmic luminosity distances and those of an empty universe, on the four subsamples separately, we recognized that the residuals were distributed symmetrically in the low redshift region, independently from the internal extinction. On the contrary, the low extinction part of the data of z ≥ 0.25 clearly showed an excess of the points with respect to an empty Universe which was not the case in the high extinction region. This diversity pointed to an interrelation between the estimated luminosity distance and internal extinction. To characterize quantitatively this interrelation we introduced a hidden variable making use of the technics of factor analysis. After subtracting that part of the residual which was explained by the hidden variable we obtained luminosity distances which were already free from interrelation with internal extinction. Fitting the corrected luminosity distances with cosmological models we concluded that the SN Ia data alone did not exclude the possibility of the Λ = 0 solution. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Carmeli's Cosmology Fits Data for an Accelerating and Decelerating Universe Without Dark Matter or Dark Energy

A new relation for the density parameter Ω is derived as a function of expansion velocity υ based on Carmeli's cosmology. This density function is used in the luminosity distance relation D L. A heretofore neglected source luminosity correction factor (1 − (υ/c)2)−1/2 is now included in D L. These relations are used to fit type Ia supernovae (SNe Ia) data, giving consistent, well-behaved fits over a broad range of redshift 0.1 < z < 2. The best fit to the data for the local density parameter is Ωm = 0.0401 ± 0.0199. Because Ωm is within the baryonic budget there is no need for any dark matter to account for the SNe Ia redshift luminosity data. From this local density it is determined that the redshift where the universe expansion transitions from deceleration to acceleration is z t = 1.095+0.264 −0.155. Because the fitted data covers the range of the predicted transition redshift z t, there is no need for any dark energy to account for the expansion rate transition. We conclude that the expansion is now accelerating and that the transition from a closed to an open universe occurred about 8.54 Gyr ago.