Results from Hubble parameter data: oscillating dark energy?

TL;DR

This work addresses whether dark energy can exhibit nontrivial dynamics by performing a model-independent analysis of $H(z)$ data. It improves a previous Lagrange-mean-value-theorem-based method by carefully propagating mid-value approximation errors and applying sensible redshift and uncertainty constraints to obtain $H'(z)$ and $q(z)$. An expanded data set of $43$ $H(z)$ measurements yields 204 $H'(z)$ and $q(z)$ data points, revealing alternating phases of accelerated and decelerated expansion and suggesting $w_x\leq w_t<-1$ around $z\approx 1.3$–$1.53$, i.e., oscillatory dark energy. These results, if confirmed with higher-precision data, could imply a nontrivial, oscillatory dark-energy component and a more nuanced expansion history of the Universe.

Abstract

Using a model-independent analysis method which bases on the Lagrange mean value theorem for obtaining the derivative of the Hubble function, we analyze $H(z)$ parameter data with some restrictive conditions. We find that: (a) the Universe may experience an accelerated expansion with a confidence level greater than 5 $σ$ at redshift $z_{101}\in (0, 0.36)$ and greater than 1.9 $σ$ at redshifts $z_{3835}\in (1.3, 1.53)$ and $z_{3836}\in (1.43, 1.53)$, where $z_j<z_{ij}<z_i$ and $i$ marks the $i$-th Hubble parameter data we consider; (b) the Universe may experience a decelerated expansion with a confidence level greater than 1.5 $σ$ at redshift $z_{2012}\in (0.40, 0.52)$; (c) $w_{\rm{x}}\leq w_{\rm{t}}<-1$ with confidence level great than 1.6 $σ$ at redshift $z_{3836}\in (1.43, 1.53)$. These results indicate that the evolution of dark energy may be oscillatory.