Revisiting Metastable Dark Energy and Tensions in the Estimation of Cosmological Parameters

TL;DR

This work tests two metastable dark-energy models against the latest cosmological data, comparing them with ΛCDM. It analyzes Model I (exponential DE decay) and Model II (DE decays into dark matter) within a flat FLRW framework, using Pantheon SNe Ia, extensive BAO data, Lyα measurements, and Planck 2018 distance priors to constrain $Ω_{m,0}h^2$, $H_0$, and the decay rate $Γ$. The study finds that while metastable models can improve SN+BAO fits, they do not meaningfully resolve the $H_0$ and $Ω_{m,0}h^2$ tensions once CMB data are included; Lyα BAO and CMB data pull the parameters in different directions, and a consistent reconciliation remains elusive. The authors conclude that simple metastable extensions are unlikely to eliminate current cosmological tensions, pointing instead to more complex expansion histories, unaccounted systematics, or non-conventional early-Universe physics as potential resolutions, with future data needed to reassess their viability.

Abstract

We investigate constraints on some key cosmological parameters by confronting metastable dark energy models with different combinations of the most recent cosmological observations. Along with the standard $Λ$CDM model, two phenomenological metastable dark energy models are considered: (\romannumeral1) DE decays exponentially, (\romannumeral2) DE decays into dark matter. We find that: (1) when considering the most recent supernovae and BAO data, and assuming a fiducial $Λ$CDM model, the inconsistency in the estimated value of the $Ω_{\rm{m,0}}h^2$ parameter obtained by either including or excluding Planck CMB data becomes very much substantial and points to a clear tension~\citep{sahni2014model,zhao2017dynamical}; (2) although the two metastable dark energy models that we study provide greater flexibility in fitting the data, and they indeed fit the SNe Ia+BAO data substantially better than $Λ$CDM, they are not able to alleviate this tension significantly when CMB data are included; (3) while local measurements of the Hubble constant are significantly higher relative to the estimated value of $H_0$ in our models (obtained by fitting to SNe Ia and BAO data), the situation seems to be rather complicated with hints of inconsistency among different observational data sets (CMB, SNe Ia+BAO and local $H_0$ measurements). Our results indicate that we might not be able to remove the current tensions among different cosmological observations by considering simple modifications of the standard model or by introducing minimal dark energy models. A complicated form of expansion history, different systematics in different data and/or a non-conventional model of the early Universe might be responsible for these tensions.

Figures (11)

• Figure 1: Observed constrains on standard $\rm{\Lambda}$CDM. Left plot gives the 1D likelihood for $\Omega_{\rm{m,0}}h^2$ and right plots shows the 1$\sigma$ and 2$\sigma$ contours for $\Omega_{\rm{m,0}}$ vs $H_0$. The cyan shadow in the right plot give $H_0$ results from riess20162 and we show the constrain results from different data sets in different color.
• Figure 2: Observed constrains on model I. The upper two plots show the marginalized 1D likelihood for $\Omega_{m,0}h^2$ (left) and $\Gamma/H_0$ (right). The lower two plots show the marginalized 1$\sigma$ and 2$\sigma$ contours for matter density vs Hubble constant (left) and $\Omega_{\rm{DE}}$ vs $\Gamma/H_0$ (right). Different color denotes for the constraint results from different data sets.
• Figure 3: The Hubble parameter $H(z)$ for the metastable DE model I obtained with different data combinations. The solid black lines and the dashed black lines show $H(z)$ from the best fit of the $\rm{\Lambda}$CDM model and the metastable DE model I with same data set, respectively.
• Figure 4: The equation of state of dark energy as a function of redshift for the metastable DE model I obtained with different data combinations. The solid black lines and the dashed black lines show $w(z)$ from the best fit of the $\rm{\Lambda}$CDM model and the metastable DE model I with same data set, respectively.
• Figure 5: The $Om$ diagnostic as a function of redshift for the metastable DE model I obtained with different data combinations. The solid black lines and the dashed black lines show $Om(z)$ from the best fit of the $\rm{\Lambda}$CDM model and the metastable DE model I with the same data set, respectively.