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A model-independent reconstruction of dark energy to very high redshift

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arxiv 2109.14848 v1 pith:F7BYSIQB submitted 2021-09-30 astro-ph.CO

classification astro-ph.CO
keywords darkenergylcdmdatadeltafreedomimprovementlarge
verification ladder T0 review T1 audit T2 compute T3 formal
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abstract

We provide a model-independent reconstruction of dark energy from $z=0$ to $ \gtrsim 10^5$. We parameterise the model by a perfect fluid with a series of physically well-motivated bins in energy-density, such that the equation of state is always $-1 \le w \le 1$. Our method is capable of describing a range of theoretical models with smooth modifications to the expansion history. Combining the latest CMB, BAO, SN and local $H_0$ measurements, we obtain a large improvement of $\Delta \chi^2=41.3$ over LCDM, at the expense of 33 additional parameters in the fit, with dark energy contributing significantly between $z \sim 10^4 - 10^5$, and intriguingly with a sound speed $c_s^2 \sim 1/3$. A significant part of the $\Delta \chi^2$ improvement comes from \Planck\ + Atacama Cosmology Telescope (\textsc{Act}) data, alleviating tension between them within LCDM. We apply a correlation prior to penalise models with unnecessary degrees of freedom and find no preference for deviations from LCDM at late-times, but moderate Bayesian evidence of an early dark energy (EDE) component. Although the model has a large amount of freedom, it is unable to reduce $S_8 \equiv \sigma_8 (\Omega_\mathrm{c} / 0.3)^{0.5}$ below that of \lcdm, to bring about full concordance with large-scale structure data.

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Cited by 5 Pith papers

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  1. The $H_0$ world cup. II. A comprehensive competition between proposed Hubble tension solutions

    astro-ph.CO 2026-07 conditional novelty 6.0 of 10

    Against a common 2025-26 dataset (Planck PR4, ACT DR6, SPT-3G, DESI DR2, Pantheon+), early dark energy and early modified gravity models win the H0 competition (~3σ residual tension), while radiation and late-time sol...

  2. Geometric Constraints on the Pre-Recombination Expansion History from the Hubble Tension

    astro-ph.CO 2026-04 unverdicted novelty 6.0 of 10

    Model-independent reconstruction shows that early-universe modifications resolving the Hubble tension exist at the background level, requiring a smooth ~15% pre-recombination expansion rate enhancement.

  3. Double the axions, half the tension: multi-field early dark energy eases the Hubble tension

    astro-ph.CO 2026-04 unverdicted novelty 6.0 of 10

    Two-field axion-like early dark energy reduces Hubble tension to 1.5 sigma residual and improves high-ell CMB fits over single-field models.

  4. The $H_0$ World Cup. I. Summary of the baseline group stage results

    astro-ph.CO 2026-07 conditional novelty 5.0 of 10

    In a systematic head-to-head analysis, early dark energy and early modified gravity models reduce the Hubble tension to about 3σ and are favored over ΛCDM, while radiation and late-time alternatives are not.

  5. Disentangling cosmic distance tensions with early and late dark energy

    astro-ph.CO 2026-04 unverdicted novelty 5.0 of 10

    Early dark energy resolves CMB-BAO tension and, combined with thawing quintessence, reduces overall cosmological tensions without phantom crossing.

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