Gaussian-process reconstructions and model building of quintom dark energy from latest cosmological observations

TL;DR

This work develops a model-independent approach to probing dark energy dynamics by applying Gaussian-process regression to a jointly analyzed set of background probes ($SNe$, $BAO$, $CC$) and growth observables ($RSD$). By reconstructing $H(z)$ and its derivative, it derives the dark-energy equation of state $w(z)$ and the normalized density $X(z)$, testing for deviations from general relativity via the growth factor parameter $\mu(z)$. The analysis identifies three dynamical-DE categories—negative-energy dark energy, late-dominated dark energy, and oscillating dark energy—and provides physical interpretations within modified gravity frameworks, scalar-field models, and EoS parametrizations, all unified under an effective-field theory (EFT) of dark energy. The results show strong concordance with $\Lambda$CDM at low redshift, while high-redshift reconstructions point to dynamical behavior and sign changes in $X(z)$, with growth data constraining large deviations from GR; EFT offers a cohesive language to compare these scenarios and to guide future observational tests.

Abstract

In this article we use the latest cosmological observations, including SNe, BAO, CC and RSD, to reconstruct the cosmological evolution via the Gaussian process. At the background level, we find consistency with the quintom dynamics for different data combinations and divide the characteristics of dark energy into three different categories, which are negative-energy dark energy, late-dominated dark energy and oscillating dark energy, respectively. Considering the effect of modified gravity on the growth of matter perturbations, the reconstruction results at the perturbative level show that we only need minor corrections to general relativity. Furthermore, we provide theoretical interpretation for the three different types of dynamical dark-energy behavior, in the framework of modified gravity, scalar fields, and dark-energy equation-of-state parametrizations. Finally, we show that all of these models can be unified in the framework of effective field theory.

Figures (6)

• Figure 1: The mean value of the reconstructed dark energy EoS parameter $w(z)$ and the normalized dark energy density parameter $X(z)$, along with the $1\sigma$ and $2\sigma$ uncertainties, for CC/SNe only and CC/SNe + BAO datasets. For comparison, we have added the yellow solid line, which shows the value of the parameters predicted by the $\Lambda$CDM paradigm. Finally, the black dashed line is added for convenience, and marks whether $w$ and $X$ change sign.
• Figure 2: The mean value of the reconstructed dark energy EoS parameter $w(z)$ and the normalized dark energy density parameter $X(z)$, along with the $1\sigma$ and $2\sigma$ uncertainties for CC + SNe and CC + SNe + BAO datasets. For comparison, we have added the yellow solid line, which shows the value of the parameters predicted by the $\Lambda$CDM paradigm. Finally, the black dashed line is added for convenience, and marks whether $w$ and $X$ change sign.
• Figure 3: The mean value of the reconstructed modified gravity parameter $\mu(z)$ along with the $1\sigma$ and $2\sigma$ uncertainties for CC/SNe + RSD and CC/SNe + RSD + BAO datasets. For comparison, we have added the yellow solid line, which shows the value of the parameters predicted by the $\Lambda$CDM paradigm. Finally, the black dashed line is added for convenience, and marks whether $w$ and $X$ change sign.
• Figure 4: An example of negative-energy dark energy model within $f(T)$ gravity. The parameter values have been chosen as $\alpha=0.9$, $b=-1.5\times 10^{-7}$, where $\alpha$ is a dimensionless parameter, while $b$ has dimensions of $H_0^{-2}$.
• Figure 5: An example for late-dominated dark energy realization within quintessence scenario. The parameter values have been chosen as $V_0=1$ and $\lambda=\sqrt{3}$, where $V_0$ has dimensions of $H_0^2$ and $\lambda$ is a dimensionless parameter. We have set the initial conditions as $\phi(z=0)=-5.4$ and $d \phi/d z(z=0)=0.2$.