scholarly journals Modified Statistical Analysis of SNe1a Data

2020 ◽  
Vol 240 ◽  
pp. 02001
Author(s):  
Lisa Goh ◽  
Cindy Ng
Keyword(s):  
Profile Likelihood ◽  
Cosmic Acceleration ◽  
Confidence Levels ◽  
Accelerating Expansion ◽  
Original Analysis ◽  
Λcdm Model ◽  
Contour Plots ◽  
Expansion Of The Universe ◽  
Best Fit ◽  
The Universe

We review an improved maximum likelihood analysis of the Type 1a Supernova (SNe1a) data. We calculate the profile likelihood in the Ωm -ΩΛ pa- rameter space by conducting a parameter sweep across the 8 SNe1a parameters, using a Markov Chain Monte Carlo (MCMC) optimization algorithm. This im- proved analysis, which does not assume arbitrary values for the uncertainties, has the advantage of being bias-free as compared to the original analysis. We use the Joint Lightcurve Analysis (JLA) dataset containing 740 SN1a data sam- ples for our study, and compare among 5 different models: the ΛCDM model, the flat wCDM model, its non-flat generalization, as well as two dynamical w(z) parametrizations. We find that the ΛCDM model is favoured over the other models, and the best fit values based on this model are Ωm =0.40 and ΩΛ =0.55. Interestingly, in most of the contour plots we obtain, the line of no acceleration is crossed at 2∼3σ confidence levels, which is similar to the results published by Nielsen et al, the original authors who introduced the improved maximum like- lihood analysis. When we generalize the wCDM model to the dynamical w(z) parametrizations, the evidence for cosmic acceleration becomes even weaker. This raises the question of how secure we can be of an accelerating expansion of the universe.

Observational data analysis for generalized cosmic Chaplygin gas in the background of Brans–Dicke theory

2021 ◽  
pp. 2150157
Author(s):  
Ujjal Debnath
Keyword(s):  
Data Analysis ◽  
State Parameter ◽  
Chaplygin Gas ◽  
Information Criteria ◽  
Model Parameters ◽  
Confidence Levels ◽  
Expansion Of The Universe ◽  
Generalized Cosmic Chaplygin Gas ◽  
Best Fit ◽  
The Universe

In this paper, we have considered the generalized cosmic Chaplygin gas (GCCG) in the background of Brans–Dicke (BD) theory and also assumed that the Universe is filled in GCCG, dark matter and radiation. To investigate the data fitting of model parameters, we have constrained the model using recent observations. Using [Formula: see text] minimum test, the best-fit values of the model parameters are determined by OHD+CMB+BAO+SNIa joint data analysis. We have drawn the contour figures for different confidence levels [Formula: see text], [Formula: see text] and [Formula: see text]. To examine the viability of the GCCG model in BD theory, we have also determined △AIC and △BIC using the information criteria (AIC and BIC). Graphically, we have analyzed the natures of the equation of state parameter and deceleration parameter for our best-fit values of model parameters. Also, we have studied the square speed of sound [Formula: see text] which lies in the interval [Formula: see text] for expansion of the Universe. So, our considered model is classically stable by considering the best-fit values of the model parameters due to the data analysis.

scholarly journals Universe opacity and Type Ia supernova dimming

2019 ◽  
Vol 489 (1) ◽  
pp. L63-L68 ◽  
Author(s):  
Václav Vavryčuk
Keyword(s):  
Cold Dark Matter ◽  
Hubble Constant ◽  
Light Extinction ◽  
Universe Model ◽  
Type Ia Supernova ◽  
Accelerating Expansion ◽  
Λcdm Model ◽  
Type Ia ◽  
Expansion Of The Universe ◽  
The Universe

ABSTRACT In this paper, I revoke a debate about an origin of Type Ia supernova (SN Ia) dimming. I argue that except for a commonly accepted accelerating expansion of the Universe, a conceivable alternative for explaining this observation is universe opacity caused by light extinction by intergalactic dust, even though it is commonly assumed that this effect is negligible. Using data of the Union2.1 SN Ia compilation, I find that the standard Λ cold dark matter (ΛCDM) model and the opaque universe model fit the SN Ia measurements at redshifts z < 1.4 comparably well. The optimum solution for the opaque universe model is characterized by the B-band intergalactic opacity $\lambda _{B} = 0.10 \pm 0.03 \, \mathrm{Gpc}^{-1}$ and the Hubble constant $H_0 = 68.0 \pm 2.5 \, \mathrm{km\, s^{-1}\, Mpc^{-1}}$. The intergalactic opacity is higher than that obtained from independent observations but still within acceptable limits. This result emphasizes that the issue of the accelerating expansion of the Universe as the origin of the SN Ia dimming is not yet definitely resolved. Obviously, the opaque universe model as an alternative to the ΛCDM model is attractive, because it avoids puzzles and controversies associated with dark energy and the accelerating expansion.

scholarly journals Almost-Pseudo-Ricci Symmetric FRW Universe with a Dynamic Cosmological Term and Equation of State

Universe ◽  
2021 ◽  
Vol 7 (7) ◽  
pp. 205
Author(s):  
Sanjay Mandal ◽  
Avik De ◽  
Tee-How Loo ◽  
Pradyumn Kumar Sahoo
Keyword(s):  
Equation Of State ◽  
Cosmological Parameters ◽  
Cosmological Term ◽  
Ricci Scalar ◽  
Energy Conditions ◽  
Late Time ◽  
Frw Universe ◽  
Accelerating Expansion ◽  
Expansion Of The Universe ◽  
The Universe

The objective of the present paper is to investigate an almost-pseudo-Ricci symmetric FRW spacetime with a constant Ricci scalar in a dynamic cosmological term Λ(t) and equation of state (EoS) ω(t) scenario. Several cosmological parameters are calculated in this setting and thoroughly studied, which shows that the model satisfies the late-time accelerating expansion of the universe. We also examine all of the energy conditions to check our model’s self-stability.

scholarly journals Hints for possible low redshift oscillation around the best fit ΛCDM model in the expansion history of the universe

2020 ◽  
Author(s):  
L Kazantzidis ◽  
H Koo ◽  
S Nesseris ◽  
L Perivolaropoulos ◽  
A Shafieloo
Keyword(s):  
Monte Carlo ◽  
Monte Carlo Simulations ◽  
Absolute Magnitude ◽  
Density Parameter ◽  
Statistical Fluctuations ◽  
Full Dataset ◽  
Λcdm Model ◽  
History Of ◽  
Best Fit ◽  
The Universe

Abstract We search for possible deviations from the expectations of the concordance ΛCDM model in the expansion history of the Universe by analysing the Pantheon Type Ia Supernovae (SnIa) compilation along with its Monte Carlo simulations using redshift binning. We demonstrate that the redshift binned best fit ΛCDM matter density parameter Ω0m and the best fit effective absolute magnitude $\cal M$ oscillate about their full dataset best fit values with considerably large amplitudes. Using the full covariance matrix of the data taking into account systematic and statistical errors, we show that at the redshifts below z ≈ 0.5 such oscillations can only occur in 4 to 5% of the Monte Carlo simulations. While statistical fluctuations can be responsible for this apparent oscillation, we might have observed a hint for some behaviour beyond the expectations of the concordance model or a possible additional systematic in the data. If this apparent oscillation is not due to statistical or systematic effects, it could be due to either the presence of coherent inhomogeneities at low z or due to oscillations of a quintessence scalar field.

Spectral redshift does not imply an accelerating expansion of the universe

2013 ◽  
Vol 26 (3) ◽  
pp. 452-456
Author(s):  
Dimitrios Laskaroudis
Keyword(s):  
Red Shift ◽  
Gravity Center ◽  
Erroneous Conclusion ◽  
Minimum Value ◽  
Accelerating Expansion ◽  
Expansion Of The Universe ◽  
The Creation ◽  
The Universe ◽  
Spectral Redshift

Spectra received from faraway heavenly objects display a redshift. In this paper, it is shown that there is a moment in time tx at which time the red shift has its minimum value. This moment is different for every object and depends on the distance of the emission from the gravity center of the object. So from the time of the creation of the object and up until the time tx, the red shift is decreasing and from that moment on it is increasing while the object, due to the expansion of the universe, continues to move away with decreasing speed. Due to the change of the red shift from decreasing to increasing, it is possible to observe faraway supernovas with a brightness that is less than what is expected. This observation leads to the erroneous conclusion that the universe is expanding with acceleration. Finally, an explanation is given to the fact that the number of quasars is decreasing in time.

scholarly journals ACCELERATING EXPANSION OF THE UNIVERSE MAY BE CAUSED BY INHOMOGENEITIES

2006 ◽  
Vol 21 (14) ◽  
pp. 1117-1125 ◽  
Author(s):  
GYULA BENE ◽  
VIKTOR CZINNER ◽  
MÁTYÁS VASÚTH
Keyword(s):  
Friedmann Equation ◽  
Additional Term ◽  
Density Fluctuations ◽  
Einstein Equations ◽  
The Other ◽  
Accelerating Expansion ◽  
Expansion Of The Universe ◽  
The Universe ◽  
Homogeneous Approximation ◽  
Spatial Inhomogeneities

We point out that, due to the nonlinearity of the Einstein equations, a homogeneous approximation in cosmology leads to the appearance of an additional term in the Friedmann equation. This new term is associated with the spatial inhomogeneities of the metric and can be expressed in terms of density fluctuations. Although it is not constant, it decays much slower (as t-2/3) than the other terms (like density) which decrease as t-2. The presence of the new term leads to a correction in the scale factor that is proportional to t2and may give account of the recently observed accelerating expansion of the universe without introducing a cosmological constant.

scholarly journals R+RG gravity with maximal Noether symmetry

2021 ◽  
Vol 2081 (1) ◽  
pp. 012028
Author(s):  
Yu E Pokrovsky
Keyword(s):  
Dimensional Space ◽  
Accelerated Expansion ◽  
Acoustic Oscillations ◽  
Riemann Curvature Tensor ◽  
Metric Tensor ◽  
Λcdm Model ◽  
Dimensional Space Time ◽  
Expansion Of The Universe ◽  
Alpha Beta ◽  
The Universe

Abstract A Noether symmetric, 3rd order polynomial in the Riemann curvature tensor R αβμν extension of the General Relativity (GR) without cosmological constant (R+RG gravity) is suggested and discussed as a possible fundamental theory of gravity in 4-dimensional space-time with the geometric part of the Lagrangian to be L R + R G = − g 2 k R ( 1 + G G P ) . Here k = 8 π G N c 4 is the Einstein constant, g = det ( g μ ν ) , g μ ν - the metric tensor, GN - the Newton constant, c - the speed of light, R = R μ ν μ ν - the Ricci scalar, G = R 2 − 4 R μ ν R μ ν + R α β μ ν R α β μ ν - the Gauss-Bonnet topological invariant, and GP - a new constant of the gravitational self-interaction to model the cosmological bounce, inflation, accelerated expansion of the Universe, etc. The best fit to the Baryon Acoustic Oscillations data for the Hubble parameter H (z) at the redshifts z<2.36 leads to G P 1 / 4 = ( 0.557 ± 0.014 ) T p c − 1 with the mean square weighted deviation from the data about 3 times smaller than for the standard cosmological (ΛCDM) model. Due to the self-gravitating term ∼RG the respective Einstein equation in the R+RG gravity contains the additional (tachyonic in the past and now) scalar (spin = 0) graviton and the perfect geometric fluid tensor with pressure-and matter-like terms equal to the respective terms in the ΛCDM model at |z| 1. Some predictions of this R+RG gravity for the Universe are also done.

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