What do the cosmological supernova data really tell us?

Abstract

Not much by themselves, aparently. We try to reconstruct the scale factor $a(t)$ of the universe from the SNe Ia data, i.e. the luminosity distance $d_L(z)$, using only the cosmological principle and the assumption that gravitation is governed by a metric theory. In our hence "model-independent," or "cosmographic" study, we fit functions to $d_L(z)$ rather than $a(t)$, since $d_L(z)$ is what is measured. We find that the acceleration history of the universe cannot be reliably determined in this approach due to the irregularity and parametrization-dependence of the results. However, adding the GRB data to the dataset cures most of the irregularities, at the cost of compromising the model-independent nature of the study slightly. Then we can determine the redshift of transition to cosmic acceleration as $z_{\mathrm{t}}\sim 0.50\pm 0.09$ for a flat universe (larger for positive spatial curvature). If Einstein gravity (GR) is assumed, we find a redshift at which the density of the universe predicted from the $d_L(z)$ data is independent of curvature. We use this point to derive an upper limit on matter density, hence a lower limit on the density of dark energy. While these limits do not improve the generally accepted ones, they are derived *only using the $d_L(z)$ data*.

27 regular LaTeX pages, 16 figures, 4 tables

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• The Hubble Diagram to Redshift >6 from 69 Gamma-Ray Bursts
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• Cosmological Applications of Pade Approximant
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• The High-z Quasar Hubble Diagram
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• Quantifying the evidence for the current speed-up of the Universe with low and intermediate-redshift data. A more model-independent approach
• Pantheon update on a model-independent analysis of cosmological supernova data
• New Generalizations of Cosmography Inspired by the Pade Approximant
• Modeling Transit Dark Energy in $f(R,L_m)$-gravity
• Transit String Dark Energy Models in $f(Q)$ Gravity
• Consistency of nonlinear interacting ghost dark energy with recent observations
• Joint Constraints on the Hubble Constant, Spatial Curvature, and Sound Horizon from the Late-time Universe with Cosmography
• Assessing the foundation and applicability of some dark energy fluid models in the Dirac-Born-Infeld framework
• Observational backreaction in discrete black holes lattice cosmological models
• Cosmological parameter constraints using phenomenological symbolic expressions: On the significance of symbolic expression complexity and accuracy
• Analysis of Pantheon+ supernova data suggests evidence of sign-changing pressure of the cosmological fluid