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Non-minimal dark sector physics and cosmological tensions

Eleonora Di Valentino, Alessandro Melchiorri, Olga Mena, Sunny Vagnozzi

TL;DR

The paper probes whether non-minimal dark sector physics, specifically DM–DE coupling and a variable dark energy equation of state, can relieve the H0 tension. It develops an extended interacting dark energy framework with stability constraints that correlate the coupling xi and w, and tests three models (ξΛCDM, ξqCDM, ξpCDM) against Planck, BAO, Pantheon, and SH0ES data using MCMC and Bayesian model comparison. The results show that coupling can raise H0 and ease tension, with the coupled vacuum model generally favored by evidence in some datasets, while coupled quintessence and phantom scenarios are more strongly disfavored when all data are included. The study highlights both the potential of non-minimal dark energy to address tensions and the challenges of model selection and BAO interpretation in IDE frameworks, suggesting ξΛCDM as the most promising avenue among the explored models.

Abstract

We explore whether non-standard dark sector physics might be required to solve the existing cosmological tensions. The properties we consider in combination are an interaction between the dark matter and dark energy components, and a dark energy equation of state $w$ different from that of the canonical cosmological constant $w=-1$. In principle, these two parameters are independent. In practice, to avoid early-time, superhorizon instabilities, their allowed parameter spaces are correlated. We analyze three classes of extended interacting dark energy models in light of the 2019 Planck CMB results and Cepheid-calibrated local distance ladder $H_0$ measurements of Riess et al. (R19), as well as recent BAO and SNeIa distance data. We find that in quintessence coupled dark energy models, where $w > -1$, the evidence for a non-zero coupling between the two dark sectors can surpass the $5σ$ significance. On the other hand, in phantom coupled dark energy models, there is no such preference for a non-zero dark sector coupling. All the models we consider significantly raise the value of the Hubble constant easing the $H_0$ tension. The addition of low-redshift BAO and SNeIa measurements leaves some residual tension with R19 but at a level that could be justified by a statistical fluctuation. Bayesian evidence considerations mildly disfavour both the coupled quintessence and phantom models, while mildly favouring a coupled vacuum scenario, even when late-time datasets are considered. We conclude that non-minimal dark energy cosmologies, such as coupled quintessence, phantom, or vacuum models, are still an interesting route towards softening existing cosmological tensions, even when low-redshift datasets and Bayesian evidence considerations are taken into account. (abstract severely abridged)

Non-minimal dark sector physics and cosmological tensions

TL;DR

The paper probes whether non-minimal dark sector physics, specifically DM–DE coupling and a variable dark energy equation of state, can relieve the H0 tension. It develops an extended interacting dark energy framework with stability constraints that correlate the coupling xi and w, and tests three models (ξΛCDM, ξqCDM, ξpCDM) against Planck, BAO, Pantheon, and SH0ES data using MCMC and Bayesian model comparison. The results show that coupling can raise H0 and ease tension, with the coupled vacuum model generally favored by evidence in some datasets, while coupled quintessence and phantom scenarios are more strongly disfavored when all data are included. The study highlights both the potential of non-minimal dark energy to address tensions and the challenges of model selection and BAO interpretation in IDE frameworks, suggesting ξΛCDM as the most promising avenue among the explored models.

Abstract

We explore whether non-standard dark sector physics might be required to solve the existing cosmological tensions. The properties we consider in combination are an interaction between the dark matter and dark energy components, and a dark energy equation of state different from that of the canonical cosmological constant . In principle, these two parameters are independent. In practice, to avoid early-time, superhorizon instabilities, their allowed parameter spaces are correlated. We analyze three classes of extended interacting dark energy models in light of the 2019 Planck CMB results and Cepheid-calibrated local distance ladder measurements of Riess et al. (R19), as well as recent BAO and SNeIa distance data. We find that in quintessence coupled dark energy models, where , the evidence for a non-zero coupling between the two dark sectors can surpass the significance. On the other hand, in phantom coupled dark energy models, there is no such preference for a non-zero dark sector coupling. All the models we consider significantly raise the value of the Hubble constant easing the tension. The addition of low-redshift BAO and SNeIa measurements leaves some residual tension with R19 but at a level that could be justified by a statistical fluctuation. Bayesian evidence considerations mildly disfavour both the coupled quintessence and phantom models, while mildly favouring a coupled vacuum scenario, even when late-time datasets are considered. We conclude that non-minimal dark energy cosmologies, such as coupled quintessence, phantom, or vacuum models, are still an interesting route towards softening existing cosmological tensions, even when low-redshift datasets and Bayesian evidence considerations are taken into account. (abstract severely abridged)

Paper Structure

This paper contains 8 sections, 7 equations, 5 figures, 6 tables.

Table of Contents

  1. Introduction
  2. Extended interacting dark energy models
  3. Models and datasets
  4. Results
  5. Coupled vacuum: $\xi\Lambda$CDM model
  6. Coupled quintessence: $\xi q$CDM model
  7. Coupled phantom: $\xi p$CDM model
  8. Conclusions

Figures (5)

  • Figure 1: Left (right) panel: Samples from Planck chains in the ($H_0$, $\Omega_m h^2$) plane for the $\xi q$CDM ($\xi p$CDM) model, color-coded by $\xi$.
  • Figure 2: Left (right) panel: $68\%$ and $95\%$ CL allowed regions in the ($w, H_0$) plane for the $\xi q$CDM ($\xi p$CDM) model For Planck alone, Planck+BAO, and Planck+R19. Note the marginal overlap between the Planck+BAO and Planck+R19 confidence regions indicating an easing of the Hubble tension.
  • Figure 3: Triangular plot showing the 2D joint and 1D marginalized posteriors of $\Omega_ch^2$, $\xi$, $H_0$, and $\Omega_m$, obtained assuming the coupled vacuum $\xi\Lambda$CDM model, for the Planck (grey contours), Planck+BAO (red contours), and Planck+R19 (blue contours) dataset combinations. The plot clearly highlights the strong correlations between these parameters.
  • Figure 4: Triangular plot showing the 2D joint and 1D marginalized posteriors of $\Omega_ch^2$, $\xi$, $w$$H_0$, and $\Omega_m$, obtained assuming the coupled quintessence $\xi q$CDM model, for the Planck (grey contours), Planck+BAO (red contours), and Planck+R19 (blue contours) dataset combinations. The plot clearly highlights the strong correlations between these parameters.
  • Figure 5: Triangular plot showing the 2D joint and 1D marginalized posteriors of $\Omega_ch^2$, $\xi$, $w$, $H_0$, and $\Omega_m$, obtained assuming the coupled phantom $\xi p$CDM model, for the Planck (grey contours), Planck+BAO (red contours), and Planck+R19 (blue contours) dataset combinations. The plot clearly highlights the strong correlations between these parameters.