Dark Sector to Restore Cosmological Concordance

Abstract

We develop a new phenomenological model that addresses current tensions between observations of the early and late Universe. Our scenario features: (i) a decaying dark energy fluid (DDE), which undergoes a transition at $z\sim 5,000$, to raise today's value of the Hubble parameter -- addressing the $H_0$ tension, and (ii) an ultra-light axion (ULA), which starts oscillating at $z\gtrsim 10^4$, to suppress the matter power spectrum -- addressing the $S_8$ tension. Our Markov Chain Monte Carlo analyses show that such a Dark Sector model fits a combination of Cosmic Microwave Background (CMB), Baryon Acoustic Oscillations, and Large Scale Structure (LSS) data slightly better than the $\Lambda$CDM model, while importantly reducing both the $H_0$ and $S_8$ tensions with late universe probes ($\lesssim 3\sigma$). Combined with measurements from cosmic shear surveys, we find that the discrepancy on $S_8$ is reduced to the $1.4\sigma$ level, and the value of $H_0$ is further raised. Adding local supernovae measurements, we find that the $H_0$ and $S_8$ tensions are reduced to the $1.4\sigma$ and $1.2\sigma$ level respectively, with a significant improvement $\Delta {\chi }^2\simeq -18$ compared to the $\Lambda$CDM model. With this complete dataset, the DDE and ULA are detected at $\simeq 4\sigma$ and $\simeq 2\sigma$, respectively. We discuss a possible particle physics realization of this model, with a dark confining gauge sector and its associated axion, although embedding the full details within microphysics remains an urgent open question. Our scenario will be decisively probed with future CMB and LSS surveys.

6+22 pages. v2: updated numerical results in the main text and in abstract; results for 2-parameters submodel and for different axion masses added to appendices; new references added. v3: typos corrected, additional comments on AIC and on "Olympics" ranking

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Cited by in corpus (31)

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• Implications for the Hubble tension from the ages of the oldest astrophysical objects
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• Updated constraints from the effective field theory analysis of BOSS power spectrum on Early Dark Energy
• No-go guide for the Hubble tension : Late-time solutions
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• Mirror Twin Higgs Cosmology: Constraints and a Possible Resolution to the $H_0$ and $S_8$ Tensions
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• Testing dark energy after pre-recombination early dark energy
• A grounded perspective on New Early Dark Energy using ACT, SPT, and BICEP/Keck
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• Addressing the Hubble and $S_8$ Tensions with a Kinetically Mixed Dark Sector
• Cosmological constraints on the Multi Scalar Field Dark Matter model
• Cascading Dark Energy
• Ultra-light axions and the kinetic Sunyaev-Zel'dovich Effect
• Altered Axion Abundance from a Dynamical Peccei-Quinn Scale
• Constraints from High-Precision Measurements of the Cosmic Microwave Background: The Case of Disintegrating Dark Matter with $\Lambda$ or Dynamical Dark Energy
• Does the fraction of dark matter diminish with early dark energy?
• Chameleon Early Dark Energy and the Hubble Tension
• Axi-Higgs cosmology: Cosmic Microwave Background and cosmological tensions
• New tests of dark sector interactions from the full-shape galaxy power spectrum
• The $H_0$ and $S_8$ tensions necessitate early and late time changes to $\Lambda$CDM