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 Shedding Light On An Undiscovered Aspect That Perfectly Mimics Cosmic Acceleration

2022 ◽  
Author(s):  
Karan R. Takkhi
Keyword(s):  
Gamma Ray ◽  
Hubble Space Telescope ◽  
High Redshift ◽  
Cosmic Acceleration ◽  
Expansion Rate ◽  
Type Ia Supernovae ◽  
Time Relationship ◽  
Type Ia ◽  
Ia Supernovae ◽  
Distance Relationship

Abstract The comparison of redshift-distance relationship for high and low-redshift supernovae revealed the surprising transition of the Universe’s expansion from deceleration to acceleration. As compared to local supernovae, remote supernovae appear 10% to 25% dimmer as they are further away than expected. The expansion rate obtained for local supernovae is higher with low redshifts as compared to the expansion rate obtained for remote supernovae with high redshifts. Since observed redshifts in an expanding Universe provide an estimate of recession velocities, therefore, it is very disturbing to find that low recession velocities (just 1% of speed of light) indicate a faster rate of expansion (acceleration), whereas high recession velocities (60% of speed of light) indicate a slower rate of expansion (deceleration). In this paper, I unravel an undiscovered aspect that perfectly mimics cosmic acceleration. Rather than “cosmic deceleration that preceded the current epoch of cosmic acceleration”, I show in this paper, that “consecutive expansion epochs of the Universe that preceded the current epoch of cosmic expansion” were responsible for placing remote supernovae further away than expected. As a consequence of consecutive expansion, expansion began for remote structures in preceding expansion epochs before it did for local structures in the current (or more recent) expansion epoch; remote supernovae, quasars, and gamma-ray bursts are therefore not only further away than expected, but they also happen to yield a slower rate of expansion, thereby suggesting their deceleration even with “superluminal expansion”. As a result of consecutive expansion, preceding expansion epochs appear to be decelerating as compared to the expansion epoch that succeeds them. The analysis is based on the redshift-distance relationship plotted for 580 type Ia supernovae from the Supernova Cosmology Project, 7 additional high-redshift type Ia supernovae discovered through the Advanced Camera for Surveys on the Hubble Space Telescope from the Great Observatories Origins Deep Survey Treasury program, and 1 additional very high-redshift type Ia supernova discovered with Wide Field and Planetary Camera 2 on the Hubble Space Telescope. The results obtained by the High-Z Supernova Search Team through observations of type Ia supernovae have also been analysed. Studies incorporating quasars and gamma-ray bursts to determine how the expansion of the Universe has changed over time have been taken into consideration as well. The results obtained in this paper have been confirmed by plotting velocity-distance relationship, expansion rate vs. time relationship, expansion factor vs. time relationship, scale factor vs. time relationship, scale factor vs. distance relationship, distance-redshift relationship, and distance modulus vs. redshift relationship, moreover, the deceleration parameter (q0) is also found to be negative (q0 < 0).

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 &lt; δ &lt; 0.071 and −0.007 &lt; Σ0 &lt; 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.

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 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 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

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 Spectra of High-Redshift Type Ia Supernovae and a Comparison with Their Low-Redshift Counterparts

2005 ◽  
Vol 130 (6) ◽  
pp. 2788-2803 ◽  
Author(s):  
I. M. Hook ◽  
D. A. Howell ◽  
G. Aldering ◽  
R. Amanullah ◽  
M. S. Burns ◽  
...  
Keyword(s):  
High Redshift ◽  
Type Ia Supernovae ◽  
Type Ia ◽  
Ia Supernovae

The Berkeley-AAO Distant Supernova Search

1991 ◽  
Vol 9 (2) ◽  
pp. 261-265 ◽  
Author(s):  
W. J. Couch ◽  
S. Perlmutter ◽  
H. J. M. Newburg ◽  
C. Pennypacker ◽  
G. Goldhaber ◽  
...  
Keyword(s):  
Mass Density ◽  
Type Ia Supernovae ◽  
Standard Candle ◽  
Type Ia ◽  
Ia Supernovae ◽  
The Universe

AbstractA search for Type Ia supernovae at cosmological distances is being undertaken in an attempt to exploit their standard candle property to constrain the mass density of the universe. We describe the rationale for such a program, the observational approach and strategy taken, and the progress made to date. The science that is being generated by the project in additional to supernova detection is also discussed briefly.

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