scholarly journals Cosmographic Parameters in Model-independent Approaches

2021 ◽  
Vol 923 (2) ◽  
pp. 274
Author(s):  
Ahmad Mehrabi ◽  
Mehdi Rezaei
Keyword(s):  
High Redshift ◽  
Data Sets ◽  
Ongoing Debate ◽  
Technical Problems ◽  
Advantages And Disadvantages ◽  
Type Ia ◽  
Cosmological Data ◽  
Model Independent ◽  
Ia Supernovae ◽  
The Universe

Abstract The cosmographic approach, a Taylor expansion of the Hubble function, has been used as a model-independent method to investigate the evolution of the universe in the presence of cosmological data. Apart from possible technical problems like the radius of convergence, there is an ongoing debate about the tensions that appear when one investigates some high-redshift cosmological data. In this work, we consider two common data sets, namely, Type Ia supernovae (Pantheon sample) and the Hubble data, to investigate advantages and disadvantages of the cosmographic approach. To do this, we obtain the evolution of cosmographic functions using the cosmographic method, as well as two other well-known model-independent approaches, namely, the Gaussian process and the genetic algorithm. We also assume a ΛCDM model as the concordance model to compare the results of mentioned approaches. Our results indicate that the results of cosmography compared with the other approaches are not exact enough. Considering the Hubble data, which are less certain, the results of q 0 and j 0 obtained in cosmography provide a tension at more than 3σ away from the best result of ΛCDM. Assuming both of the data samples in different approaches, we show that the cosmographic approach, because it provides some biased results, is not the best approach for reconstruction of cosmographic functions, especially at higher redshifts.

scholarly journals Model-independent cosmic acceleration and redshift-dependent intrinsic luminosity in type-Ia supernovae

2019 ◽  
Vol 625 ◽  
pp. A15 ◽  
Author(s):  
I. Tutusaus ◽  
B. Lamine ◽  
A. Blanchard
Keyword(s):  
Spline Interpolation ◽  
High Redshift ◽  
Cosmic Acceleration ◽  
Expansion Rate ◽  
Type Ia Supernovae ◽  
Type Ia ◽  
Model Independent ◽  
Ia Supernovae ◽  
The Universe ◽  
Intrinsic Luminosity

Context. The cosmological concordance model (ΛCDM) is the current standard model in cosmology thanks to its ability to reproduce the observations. The first observational evidence for this model appeared roughly 20 years ago from the type-Ia supernovae (SNIa) Hubble diagram from two different groups. However, there has been some debate in the literature concerning the statistical treatment of SNIa, and their stature as proof of cosmic acceleration. Aims. In this paper we relax the standard assumption that SNIa intrinsic luminosity is independent of redshift, and examine whether it may have an impact on our cosmological knowledge and more precisely on the accelerated nature of the expansion of the universe. Methods. To maximise the scope of this study, we do not specify a given cosmological model, but we reconstruct the expansion rate of the universe through a cubic spline interpolation fitting the observations of the different cosmological probes: SNIa, baryon acoustic oscillations (BAO), and the high-redshift information from the cosmic microwave background (CMB). Results. We show that when SNIa intrinsic luminosity is not allowed to vary as a function of redshift, cosmic acceleration is definitely proven in a model-independent approach. However, allowing for redshift dependence, a nonaccelerated reconstruction of the expansion rate is able to fit, at the same level of ΛCDM, the combination of SNIa and BAO data, both treating the BAO standard ruler rd as a free parameter (not entering on the physics governing the BAO), and adding the recently published prior from CMB observations. We further extend the analysis by including the CMB data. In this case we also consider a third way to combine the different probes by explicitly computing rd from the physics of the early universe, and we show that a nonaccelerated reconstruction is able to nicely fit this combination of low- and high-redshift data. We also check that this reconstruction is compatible with the latest measurements of the growth rate of matter perturbations. We finally show that the value of the Hubble constant (H0) predicted by this reconstruction is in tension with model-independent measurements. Conclusions. We present a model-independent reconstruction of a nonaccelerated expansion rate of the universe that is able to fit all the main background cosmological probes nicely. However, the predicted value of H0 is in tension with recent direct measurements. Our analysis points out that a final reliable and consensual value for H0 is critical to definitively prove cosmic acceleration in a model-independent way.

scholarly journals Testing the isotropy of the Universe with Type Ia supernovae in a model-independent way

2017 ◽  
Vol 474 (3) ◽  
pp. 3516-3522 ◽  
Author(s):  
Yu-Yang Wang ◽  
F Y Wang
Keyword(s):  
Dark Energy ◽  
Equation Of State ◽  
Light Curve ◽  
Type Ia Supernovae ◽  
Anisotropic Universe ◽  
Preferred Direction ◽  
Type Ia ◽  
Model Independent ◽  
Ia Supernovae ◽  
The Universe

Abstract In this paper, we study an anisotropic universe model with Bianchi-I metric using Joint light-curve analysis (JLA) sample of Type Ia supernovae (SNe Ia). Because light-curve parameters of SNe Ia vary with different cosmological models and SNe Ia samples, we fit the SNe Ia light-curve parameters and cosmological parameters simultaneously employing Markov chain Monte Carlo method. Therefore, the results on the amount of deviation from isotropy of the dark energy equation of state (δ), and the level of anisotropy of the large-scale geometry (Σ0) at present, are totally model-independent. The constraints on the skewness and cosmic shear are −0.101 < δ < 0.071 and −0.007 < Σ0 < 0.008. This result is consistent with a standard isotropic universe (δ = Σ0 = 0). However, a moderate level of anisotropy in the geometry of the Universe and the equation of state of dark energy, is allowed. Besides, there is no obvious evidence for a preferred direction of anisotropic axis in this model.

Toward cosmological-model-independent calibrations for the luminosity relations of Gamma-Ray Bursts

2015 ◽  
Vol 24 (07) ◽  
pp. 1550057 ◽  
Author(s):  
Xuheng Ding ◽  
Zhengxiang Li ◽  
Zong-Hong Zhu
Keyword(s):  
Cosmological Model ◽  
Gamma Ray ◽  
Distance Estimation ◽  
Gamma Ray Bursts ◽  
Type Ia ◽  
Model Independent ◽  
Global Fit ◽  
Ia Supernovae ◽  
Distance Indicators ◽  
The Universe

Gamma-ray bursts (GRBs), have been widely used as distance indicators to measure the cosmic expansion and explore the nature of dark energy. A popular method adopted in previous works is to calibrate the luminosity relations which are responsible for distance estimation of GRBs with more primary (low redshift) cosmic distance ladder objects, type Ia supernovae (SNe Ia). Since distances of SNe Ia in all SN Ia samples used to calibrate GRB luminosity relations were usually derived from the global fit in a specific cosmological model, the distance of GRB at a given redshift calibrated with matching SNe Ia was still cosmological-model-dependent. In this paper, we first directly determine the distances of SNe Ia with the Angular Diameter Distances (ADDs) of galaxy clusters without any assumption for the background of the universe, and then calibrate GRB luminosity relations with our cosmology-independent distances of SNe Ia. The results suggest that, compared to the previous original manner where distances of SNe Ia used as calibrators are determined from the global fit in a particular cosmological model, our treatments proposed here yield almost the same calibrations of GRB luminosity relations and the cosmological implications of them do not suffer any circularity.

scholarly journals CONSTRAINTS ON THE COSMOLOGICAL DENSITY PARAMETERS AND COSMIC TOPOLOGY

2007 ◽  
Vol 16 (02n03) ◽  
pp. 207-217 ◽  
Author(s):  
M. J. REBOUÇAS
Keyword(s):  
Mass Fraction ◽  
Type Ia Supernovae ◽  
Data Sets ◽  
X Ray ◽  
Set Constraints ◽  
Type Ia ◽  
Ia Supernovae ◽  
The Universe ◽  
Nontrivial Topology ◽  
Spatial Section

A nontrivial topology of the spatial section of the universe is an observable which can be probed for all homogeneous and isotropic universes, without any assumption on the cosmological density parameters. We discuss how one can use this observable to set constraints on the density parameters of the universe by using a specific spatial topology along with type Ia supernovae and X-ray gas mass fraction data sets.

scholarly journals SNe Ia as a cosmological probe

2015 ◽  
Vol 24 (14) ◽  
pp. 1530029 ◽  
Author(s):  
Xiangcun Meng ◽  
Yan Gao ◽  
Zhanwen Han
Keyword(s):  
Dark Energy ◽  
Equation Of State ◽  
High Redshift ◽  
Type Ia Supernovae ◽  
Analysis Techniques ◽  
Type Ia ◽  
History Of ◽  
Acceleration Of The Universe ◽  
Ia Supernovae ◽  
The Universe

Type Ia supernovae (SNe Ia) luminosities can be corrected in order to render them useful as standard candles that are able to probe the expansion history of the universe. This technique was successfully applied to discover the present acceleration of the universe. As the number of SNe Ia observed at high redshift increases and analysis techniques are perfected, people aim to use this technique to probe the equation-of-state of the dark energy (EOSDE). Nevertheless, the nature of SNe Ia progenitors remains controversial and concerns persist about possible evolution effects that may be larger and harder to characterize than the more obvious statistical uncertainties.

FRW cosmology in f(R,T) gravity

2019 ◽  
Vol 16 (02) ◽  
pp. 1950024 ◽  
Author(s):  
Nisha Godani
Keyword(s):  
Polynomial Function ◽  
High Redshift ◽  
Apparent Magnitude ◽  
Type Ia Supernovae ◽  
Type Ia ◽  
Frw Model ◽  
Age Of The Universe ◽  
Hubble Parameters ◽  
Ia Supernovae ◽  
The Universe

In the present paper, the work of Moreas et al. [P. H. R. S. Moraes, G. Ribeiro and R. A. C. Correa, A transition from a decelerated to an accelerated phase of the universe expansion from the simplest non-trivial polynomial function of T in the [Formula: see text] formalism, Astrophys. Space Sci. 361 (2016) 227–231] is extended to study the FRW model in [Formula: see text] gravity. The expressions for deceleration and Hubble parameters are determined in terms of redshift. The age of the universe is established using [Formula: see text] high-redshift type Ia supernovae data from the Supernova cosmology project and 15 low-redshift type Ia supernovae data from the Calán/Tolono Supernova survey [S. Permutter et al., Measurements of Omega and Lambda from 42 High-Redshift Supernovae, Astrophys. J. 517 (1999) 565–585]. For these redshifts, the data of observed apparent magnitude and luminosity distance are used for the comparison with the obtained theoretical values.

scholarly journals Expansion of the Universe and cosmological redshift

2021 ◽  
Author(s):  
Vaclav Vavrycuk
Keyword(s):  
Dark Energy ◽  
Light Propagation ◽  
High Redshift ◽  
Cosmic Time ◽  
Unsuccessful Attempt ◽  
Cosmological Redshift ◽  
Type Ia ◽  
Ia Supernovae ◽  
High Redshift Universe ◽  
The Universe

Abstract The re-examination of light propagation in space described by the Friedmann-Lemaitre-Robertson-Walker (FLRW) metric reveals surprisingly that this metric does not predict the cosmological redshift as so far incorrectly supposed. It is shown that the change in the frequency of light is always connected with time dilation, similarly as for the gravitational redshift. Therefore, the conformal time must be considered as the cosmic time at the high redshift universe and the original FLRW metric must be substituted by its conformal version. The correctness of the proposed conformal metric is convincingly confirmed by Type Ia supernovae (SNe Ia) observations. The standard FLRW metric produces essential discrepancy with the SNe Ia observations called the ‘supernova dimming’, and consequently dark energy has to be introduced to comply theoretical predictions with data. By contrast, the conformal FLRW metric fits data well with no need to introduce any new free parameter. Hence, the discovery of the supernova dimming actually revealed the failure of the FLRW metric and introducing dark energy was just an unsuccessful attempt to cope with the problem within this false metric. Obviously, adopting the conformal FLRW metric for describing the evolution of the Universe has fundamental cosmological consequences.

scholarly journals Defying the laws of gravity I: model-independent reconstruction of the Universe expansion from growth data

2020 ◽  
Vol 494 (1) ◽  
pp. 819-826 ◽  
Author(s):  
Benjamin L’Huillier ◽  
Arman Shafieloo ◽  
David Polarski ◽  
Alexei A Starobinsky
Keyword(s):  
Type Ia Supernovae ◽  
Growth Data ◽  
Growth History ◽  
Type Ia ◽  
History Of ◽  
Space Distortion ◽  
Model Independent ◽  
Ia Supernovae ◽  
The Universe

ABSTRACT Using redshift space distortion data, we perform model-independent reconstructions of the growth history of matter inhomogeneity in the expanding Universe using two methods: crossing statistics and Gaussian processes. We then reconstruct the corresponding history of the Universe background expansion and fit it to Type Ia supernovae data, putting constraints on (Ωm, 0, σ8, 0). The results obtained are consistent with the concordance flat-ΛCDM model and General Relativity as the gravity theory given the current quality of the inhomogeneity growth data.

scholarly journals The ESO’s VLT type Ia supernova spectral set of the final two years of SNLS

2018 ◽  
Vol 614 ◽  
pp. A134 ◽  
Author(s):  
C. Balland ◽  
F. Cellier-Holzem ◽  
C. Lidman ◽  
P. Astier ◽  
M. Betoule ◽  
...  
Keyword(s):  
High Redshift ◽  
Host Galaxy ◽  
Data Sets ◽  
Host Galaxies ◽  
Spectral Evolution ◽  
Local Color ◽  
Galaxy Surveys ◽  
Type Ia ◽  
Spectral Set ◽  
Ia Supernovae

Aims. We aim to present 70 spectra of 68 new high-redshift type Ia supernovae (SNe Ia) measured at ESO’s VLT during the final two years of operation (2006–2008) of the Supernova Legacy Survey (SNLS). This new sample complements the VLT three year spectral set. Altogether, these two data sets form the five year sample of SNLS SN Ia spectra measured at the VLT on which the final SNLS cosmological analysis will partly be based. In the redshift range considered, this sample is unique in terms of homogeneity and number of spectra. We use it to investigate the possibility of a spectral evolution of SNe Ia populations with redshift as well as SNe Ia spectral properties as a function of lightcurve fit parameters and the mass of the host-galaxy. Methods. Reduction and extraction are based on both IRAF standard tasks and our own reduction pipeline. Redshifts are estimated from host-galaxy lines whenever possible or alternatively from supernova features. We used the spectro-photometric SN Ia model SALT2 combined with a set of galaxy templates that model the host-galaxy contamination to assess the type Ia nature of the candidates. Results. We identify 68 new SNe Ia with redshift ranging from z = 0.207 to z = 0.98 for an average redshift of z = 0.62. Each spectrum is presented individually along with its best-fit SALT2 model. Adding this new sample to the three year VLT sample of SNLS, the final dataset contains 209 spectra corresponding to 192 SNe Ia identified at the VLT. We also publish the redshifts of other candidates (host galaxies or other transients) whose spectra were obtained at the same time as the spectra of live SNe Ia. This list provides a new redshift catalog useful for upcoming galaxy surveys. Using the full VLT SNe Ia sample, we build composite spectra around maximum light with cuts in color, the lightcurve shape parameter (“stretch”), host-galaxy mass and redshift. We find that high-z SNe Ia are bluer, brighter and have weaker intermediate mass element absorption lines than their low-z counterparts at a level consistent with what is expected from selection effects. We also find a flux excess in the range [3000–3400] Å for SNe Ia in low mass host-galaxies (M < 1010M⊙) or with locally blue U–V colors, and suggest that the UV flux (or local color) may be used in future cosmological studies as a third standardization parameter in addition to stretch and color.

scholarly journals Model-independent reconstruction of the expansion history of the Universe from Type Ia supernovae

2011 ◽  
Vol 419 (1) ◽  
pp. 513-521 ◽  
Author(s):  
S. Benitez-Herrera ◽  
F. Röpke ◽  
W. Hillebrandt ◽  
C. Mignone ◽  
M. Bartelmann ◽  
...  
Keyword(s):  
Type Ia Supernovae ◽  
Type Ia ◽  
History Of ◽  
Model Independent ◽  
Ia Supernovae ◽  
The Universe
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