Determination of the deceleration parameter from supernovae data

Monthly Notices of the Royal Astronomical Society, 2022

We study a parametrization of the deceleration parameter in a tilted universe, namely a cosmological model equipped with two families of observers. The first family follows the smooth Hubble flow, while the second is the real observers residing in a typical galaxy inside a bulk flow and moving relative to the smooth Hubble expansion with finite peculiar velocity. We use the compilation of Type Ia Supernovae (SnIa) data, as described in the Pantheon dataset, to find the quality of fit to the data and study the redshift evolution of the deceleration parameter. In so doing, we consider two alternative scenarios, assuming that the bulk-flow observers live in the ΛCDM and in the Einstein-de Sitter universe. We show that a tilted Einstein-de Sitter model can reproduce the recent acceleration history of the universe, without the need of a cosmological constant or dark energy, by simply taking into account linear effects of peculiar motions. By means of a Markov Chain Monte Carlo (MCMC) method, we also constrain the magnitude and the uncertainties of the parameters of the two models. From our statistical analysis, we find that the tilted Einstein-de Sitter model, equipped with one or two additional parameters that describe the assumed large-scale velocity flows, performs similar to the standard ΛCDM paradigm in the context of model selection criteria (Akaike Information Criterion and Bayesian Information Criterion).

Journal of Cosmology and Astroparticle Physics, 2014

We further investigate slowing down of acceleration of the universe scenario for five parametrizations of the equation of state of dark energy using four sets of Type Ia supernovae data. In a maximal probability analysis we also use the baryon acoustic oscillation and cosmic microwave background observations. We found the low redshift transition of the deceleration parameter appears, independently of the parametrization, using supernovae data alone except for the Union 2.1 sample. This feature disappears once we combine the Type Ia supernovae data with high redshift data. We conclude that the rapid variation of the deceleration parameter is independent of the parametrization. We also found more evidence for a tension among the supernovae samples, as well as for the low and high redshift data.

Journal of Cosmology and Astroparticle Physics, 2004

We investigate the behaviour of dark energy using the recently released supernova data of Riess et al., 2004 and a model independent parameterization for dark energy (DE). We find that, if no priors are imposed on Ω 0m and h, DE which evolves with time provides a better fit to the SNe data than ΛCDM. This is also true if we include results from the WMAP CMB data. From a joint analysis of SNe+CMB, the best-fit DE model has w 0 < ∼ − 1 at the present epoch and the transition from deceleration to acceleration occurs at z T = 0.39±0.03. However, DE evolution becomes weaker if the ΛCDM based CMB results Ω 0m = 0.27 ± 0.04, h = 0.71 ± 0.06 are incorporated in the analysis. In this case, z T = 0.57 ± 0.07. Our results also show that the extent of DE evolution is sensitive to the manner in which the supernova data is sampled.

Physical Review D, 2005

We use the Type Ia Supernova gold sample data of Riess et al in order to constrain three models of dark energy. We study the Cardassian model, the Dvali-Turner gravity modified model, and the generalized Chaplygin gas model of dark energy-dark matter unification. In our best-fit analysis for these three dark energy proposals we consider the flat model and the nonflat model priors. We also discuss the degeneracy of the models with the XCDM model through the computation of the so-called jerk parameter.

Foundations of Physics Letters, 2006

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.

The Astrophysical Journal, 2008

We extend and apply a model-independent analysis method developed earlier by Daly & Djorgovski to new samples of supernova standard candles, radio galaxy and cluster standard rulers, and use it to constrain physical properties of the dark energy as functions of redshift. Similar results are obtained for the radio galaxy and supernova data sets, which rely upon completely independent methods, suggesting that systematic errors are relatively small for both types of distances; distances to SZ clusters show a scatter which cannot be explained by the quoted measurement errors. The first and second derivatives of the distance are compared directly with predictions in a standard model based on General Relativity. The good agreement indicates that General Relativity provides an accurate description of the data on look-back time scales of about ten billion years. The first and second derivatives are combined to obtain the acceleration parameter q(z), assuming only the validity of the Robertson-Walker metric, independent of a theory of gravity and of the physical nature of the dark energy. The data are analyzed using a sliding window fit and using fits in independent

The European Physical Journal Plus 129 (2014) 22 [arXiv:1305.5190v2 [gr-qc]]

We study linearly varying deceleration parameter in terms of cosmic time t (LVDPt) with the companion linearly varying deceleration parameter in terms of cosmic redshift z (LVDPz) and in terms of cosmic scale factor a (LVDPa). We investigate in detail the kinematics and the fate of the Universe by confronting the three LVDP laws with the latest observational data from H(z) compilation (25 data points) and SN Ia Union2.1 compilation (580 data points). The study reveals that the LVDPt law is superior than LVDPz and LVDPa laws in many aspects. In particular, the goodness of fit to the observational data is found to be the best for the LVDPt law. The kinematics and dynamics (assuming general relativity) of the Universe is further studied by considering the LVDPt law in comparison with the standard LCDM model. It is found that these two models are observationally indistinguishable but the LVDPt fits the data slightly better than the LCDM model. These two models exhibit a very similar behavior for a long passage of time but make slightly different predictions for the earlier times of the Universe with considerably different predictions on the future of the Universe. According to the LVDPt model, the accelerating expansion of the Universe started when the Universe was 7.148+/-0.923 Gyr old at redshift 0.703+0.356/-0.148 and the age of the present Universe is 13.460+/-0.899 Gyr, whereas these values are found to be 7.233+/-0.225 Gyr, 0.682+/-0.082 and 13.389+/-0.289 Gyr in the LCDM model. Observational constraints on cosmic doomsday are carried out in the context of the LVDPt model, and it is found that the Universe will end in Big Rip when the age of the Universe is 36.602+/-7.930 Gyr.

Monthly Notices of the Royal Astronomical Society, 2020

Recently, a phenomenologically emergent dark energy (PEDE) model was presented with a dark energy density evolving as $\widetilde{\Omega }_{\rm {DE}}(z) = \Omega _{\rm {DE,0}}[ 1 - {\rm {tanh}}({\log }_{10}(1+z))]$, i.e. with no degree of freedom. Later on, a generalized model was proposed by adding one degree of freedom to the PEDE model, encoded in the parameter Δ. Motivated by these proposals, we constrain the parameter space ($h,\Omega _m^{(0)}$) and ($h,\Omega _m^{(0)}, \Delta$) for PEDE and generalized emergent dark energy (GEDE), respectively, by employing the most recent observational (non-)homogeneous and differential age Hubble data. Additionally, we reconstruct the deceleration and jerk parameters and estimate yield values at z = 0 of $q_0 = -0.784^{+0.028}_{-0.027}$ and $j_0 = 1.241^{+0.164}_{-0.149}$ for PEDE and $q_0 = -0.730^{+0.059}_{-0.067}$ and $j_0 = 1.293^{+0.194}_{-0.187}$ for GEDE using the homogeneous sample. We report values on the deceleration–acceleration t...

Journal of Cosmology and Astroparticle Physics, 2006

We present a simple mechanism which can mimic dark energy with an equation of state w < -1 as deduced from the supernova data. We imagine that the universe is accelerating under the control of a quintessence field, which is moving up a very gently sloping potential. As a result, the potential energy and hence the acceleration increases at lower redshifts. Fitting this behavior with a dark energy model with constant w would require w < -1. In fact we find that the choice of parameters which improves the fit to the SNe mimics w = -1.4 at low redshifts. Running up the potential in fact provides the best fit to the SN data for a generic quintessence model. However, unlike models with phantoms, our model does not have negative energies or negative norm states. Future searches for supernovae at low redshifts 0.1 < z < 0.5 and at high redshifts z > 1 may be a useful probe of our proposal.

Astrophys Space Sci 369, 17, 2024

Measurements of the current expansion rate of the Universe, H0, using standard candles, disagree with those derived from observations of the Cosmic Microwave Background (CMB). This discrepancy, known as the Hubble tension, is substantial and suggests the possibility of revisions to the standard cosmological model (Cosmological constant Λ and cold dark matter-ΛCDM). Dynamic dark energy (DE) models that introduce deviations in the expansion history relative to ΛCDM could potentially explain this tension. We used Type Ia supernovae (SNe) data to test a dynamic DE model consisting of an equation of state that varies linearly with the cosmological scale factor a. To evaluate this model, we developed a new statistic (the Tα statistic) used in conjunction with an optimization code that minimizes its value to obtain model parameters. The Tα statistic reduces bias errors (in comparison to the χ 2 statistic) because it retains the sign of the residuals, which is meaningful in testing the dynamic DE model as the deviations in the expansion history introduced by this model act asymmetrically in redshift space. The DE model fits the SNe data reasonably well, but the available SNe data lacks the statistical power to discriminate between ΛCDM and alternative models. To further assess the model using CMB data, we computed the distance to the last scattering surface and compared the results with that derived from the Planck observations. Although the simple dynamic DE model tested does not completely resolve the tension, it is not ruled out by the data and could still play a role alongside other physical effects.