Papers › Dark Sector to Restore Cosmological Concordance
Dark Sector to Restore Cosmological Concordance
Itamar J. Allali, Mark P. Hertzberg, Fabrizio Rompineve
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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 ∼5,000, to raise today's value of the Hubble parameter -- addressing the H₀ tension, and (ii) an ultra-light axion (ULA), which starts oscillating at z≳10⁴, to suppress the matter power spectrum -- addressing the S₈ 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 ΛCDM model, while importantly reducing both the H₀ and S₈ tensions with late universe probes (≲3σ). Combined with measurements from cosmic shear surveys, we find that the discrepancy on S₈ is reduced to the 1.4σ level, and the value of H₀ is further raised. Adding local supernovae measurements, we find that the H₀ and S₈ tensions are reduced to the 1.4σ and 1.2σ level respectively, with a significant improvement Δχ²≃-18 compared to the ΛCDM model. With this complete dataset, the DDE and ULA are detected at ≃4σ and ≃2σ, 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.
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