Non-minimal dark sector physics and cosmological tensions (1910.09853v2)

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 $5\sigma$ 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)

• The paper investigates non-minimal dark sector models with interacting dark energy and dark matter to address discrepancies in cosmological data like the Hubble tension.
• Analysis shows these models, particularly interacting quintessence, reduce the H0 tension from 4.3σ to about 2.5σ and find strong statistical evidence for interaction.
• This work suggests non-minimal dark sector physics is a promising avenue for resolving cosmological tensions but requires future observations for full validation.

Overview of Non-minimal Dark Sector Physics and Cosmological Tensions

The paper "Non-minimal dark sector physics and cosmological tensions" aims to address significant discrepancies observed in cosmological data by investigating interactions between dark matter (DM) and dark energy (DE). The authors, Eleonora Di Valentino, Alessandro Melchiorri, Olga Mena, and Sunny Vagnozzi, paper models where DE does not conform to the usual cosmological constant scenario, potentially ameliorating tensions such as that in the Hubble constant ($H_0$).

Key Objectives and Methodology

The research focuses on models that allow for a DE equation of state $w \neq -1$, potentially indicating quintessence ($w > -1$) or phantom energy ($w < -1$). Additionally, the paper examines the possibility of an interaction between DM and DE, parameterized by a coupling constant, $\xi$. These models are evaluated using a combination of datasets, including 2019 Planck Cosmic Microwave Background (CMB) data, Cepheid-calibrated local distance ladder (R19) measurements, and recent Baryon Acoustic Oscillation (BAO) and Type Ia Supernovae (SNeIa) data.

The paper rigorously analyzes the constraints on these parameters to assess their potential in resolving the $H_0$ tension. The authors employ Markov Chain Monte Carlo methods to estimate the posterior distributions of the cosmological parameters and calculate the Bayes factor for model comparison against the standard $\Lambda$CDM scenario.

Noteworthy Results

1. Parameter Correlation and Stability: The paper reveals that to maintain stability and avoid early-time cosmological instabilities, the DE equation of state $w$ and the coupling parameter $\xi$ are correlated. The analysis distinguishes between quintessence models where $\xi < 0$ and $w > -1$, and phantom models where $\xi > 0$ and $w < -1$.
2. Alleviation of the $H_0$ Tension: All investigated models, particularly $\xi \Lambda$CDM, exhibit a capacity to raise the inferred value of the Hubble constant, reducing tension with local $H_0$ measurements. Notably, for models where the DE behaves as quintessence, there is a preference for $w > -1$, achieving concordance with data within approximately three standard deviations.
3. Statistical Preference for Interaction: In models like quintessence coupled dark energy, evidence for a non-zero coupling between the dark sectors can exceed $5\sigma$. These models demonstrate compatibility with existing data while mitigating the $H_0$ tension from a $4.3\sigma$ tension in $\Lambda$CDM down to about $2.5\sigma$ when considering Planck and BAO combination.
4. Implications for DE Models: Despite statistical fluctuations, the predictions of quintessence models with interaction suggest that they can offer a superior fit to observational data compared to non-interacting counterparts.

Theoretical and Practical Implications

This exploration into the non-standard dark sector scenarios provides an intriguing pathway for addressing cosmological tensions, particularly the $H_0$ discrepancy. The implications extend towards refining our understanding of DE's role in the universe's expansion history. However, these models, though promising, need further scrutiny through future experimental and observational advancements in high-precision cosmology.

Speculations for Future Developments

Continued observations, especially those from next-generation CMB experiments and large-scale structure surveys, could significantly impact the parameter space of these non-minimal dark sector models. Additionally, theoretical developments that integrate these findings within a broader framework of particle physics might yield further insights into the fundamental properties of DE and DM interactions. The potential for new physics revealed by this work is promising and underscores the necessity of rethinking standard cosmological paradigms.

In conclusion, this paper makes a compelling case for considering non-minimal dark sector physics as a viable resolution to present-day cosmological tensions, urging for comprehensive future studies that further investigate these models' validity and consequences.