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Dark Energy at early times and ACT: a larger Hubble constant without late-time priors
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Dark Energy at early times and ACT: a larger Hubble constant without late-time priors
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In this paper we fit two models of Early Dark Energy (EDE) (an increase in the expansion rate before recombination) to the combination of Atacama Cosmology Telescope (ACT) measurements of the Cosmic Microwave Background (CMB) with data from either the WMAP or the Planck satellite, along with measurements of the baryon acoustic oscillations and uncalibrated supernovae luminosity distance. We study a phenomenological axion-like potential ('axEDE') and a scalar field experiencing a first-order phase-transition ('NEDE'). We find that for both models the 'Planck-free' analysis yields non-zero EDE at > 2 sigma and an increased value for $H_0 \sim 70-74$ km/s/Mpc, compatible with local measurements, without the inclusion of any prior on $H_0$. On the other hand, the inclusion of Planck data restricts the EDE contribution to an upper-limit only at 95% C.L. For axEDE, the combination of Planck and ACT leads to constraints 30% weaker than with Planck alone, and there is no residual Hubble tension. On the other hand, NEDE is more strongly constrained in a Planck+ACT analysis, and the Hubble tension remains at $\sim 3\sigma$, illustrating the ability for CMB data to distinguish between EDE models. We explore the apparent inconsistency between the Planck and ACT data and find that it comes (mostly) from a slight tension between the temperature power spectrum at multipoles around $\sim 1000$ and $\sim 1500$. Finally, through a mock analysis of ACT data, we demonstrate that the preference for EDE is not driven by a lack of information at high-$\ell$ when removing Planck data, and that a LCDM fit to the fiducial EDE cosmology results in a significant bias on $\{H_0,\omega_{\rm cdm}\}$. More accurate measurements of the TT power spectra above $\ell\sim 2500$ and EE between $\ell \sim 300-500$ will play a crucial role in differentiating EDE models.
Forward citations
Cited by 10 Pith papers
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Any unified early and late dark energy scenario with a single tracking scalar field requires a potential with three distinct slopes arranged in a steep-steeper-shallow hierarchy.
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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.
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The local Hubble constant is measured as 73.04 ± 1.04 km/s/Mpc from Cepheid-calibrated Type Ia supernovae, showing a 5-sigma discrepancy with the Planck+LCDM prediction.
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Hubble tension: a short review of theoretical explanations
A comprehensive review finds no theoretical Hubble-tension solution yet passes all consistency tests; new early-dark-energy chains reach high H0 only when the SH0ES calibration is added.
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Imprint of swampland-inspired coupled early dark energy
A swampland-inspired DM-EDE coupling is tested against DESI DR2 BAO data, showing the EDE potential construction affects late-time dark energy constraints.
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Cosmological Viability of Exponential Infrared $f(T)$ Gravity
Exponential IR f(T) gravity Model I alleviates Hubble tension but is disfavoured by combined Planck/ACT/SPT+DESI+Pantheon+ data; Model II is ruled out because background constraints force unphysical shifts in CMB parameters.
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What it takes to solve the Hubble tension through Modifications of Cosmological Recombination II: in light of ACT DR6 and DESI DR2
Perturbative modifications to the electron mass m_e(z) resolve the Hubble tension with Planck+ACT CMB data but cannot when DESI DR2 BAO data are added due to lowered Omega_m.
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The Hubble tension: A decade review
Pure early or late fixes to the Hubble tension are tightly constrained; remaining options are combined early-late interacting dark energy or new physics at the local-to-homogeneous transition.
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The Hubble tension: A decade review
A review summarizing the Hubble tension as a persistent crisis and discussing resolutions via interacting dark energy models that combine early-time and late-time modifications.
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The Hubble Tension and Early Dark Energy
The Hubble tension between local and early-universe expansion-rate measurements may be resolved by early dark energy that speeds up expansion before recombination while satisfying existing constraints.
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