Dark Energy at early times and ACT: a larger Hubble constant without late-time priors

Abstract

Recent observations using the Atacama Cosmology Telescope (ACT) have provided ground-based cosmic microwave background (CMB) maps with higher angular resolution than the Planck satellite. These have the potential to put interesting constraints on models resolving the 'Hubble tension'. In this paper we fit two models of Early Dark Energy (EDE) (an increase in the expansion rate around matter/radiation equality) to the combination of ACT data with large-scale measurements of the CMB either from the WMAP or the Planck satellite (including lensing), 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 phasetransition ('NEDE'). We find that for both models the 'Planck-free' analysis yields non-zero EDE at 2σ and an increased value for H0 ∼ 70 − 74 km/s/Mpc, compatible with local measurements, without the inclusion of any prior on H0. 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 ∼ 3σ, illustrating the ability for CMB data to distinguish between different EDE models. We further 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 ∼ 1000 and ∼ 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-when removing Planck data, and that a ΛCDM fit to the fiducial EDE cosmology results in a significant bias on {H0, ω cdm }. More accurate measurements of the TT CMB power spectra above ∼ 2500 and EE between ∼ 300 − 500 will play a crucial role in differentiating between EDE models.

The Early Dark Sector, the Hubble Tension, and the Swampland

“…Meanwhile, the preference for a non-zero EDE component is strengthened (as found in [56,69,81]): we find the marginalized constraint f EDE = 0.108 +0.053 −0.023 when ACT is included, compared to f EDE = 0.099 +0.056 −0.041 without ACT data. However, the f EDE posterior distribution in Fig.…”

“…The ACT collaboration analyzed the EDE model in [56] and found that ACT data combined with low-Planck T T data ( < 650, similar to WMAP ) mildly prefer a non-zero f EDE at ≈ 3σ significance (see also [69] and [70]). When combining ACT with the full Planck data set, this preference is no longer seen, due to the dominant statistical weight of Planck (which does not prefer EDE on its own).…”

Hot New Early Dark Energy: Towards a Unified Dark Sector of Neutrinos, Dark Energy and Dark Matter

“…During the NEDE phase transition ψ ≡ √ 2|Ψ 0 | → v Ψ , which implies a breaking of the global U(1) L and, as shown before, gives a mass to the active neutrinos. From (15) we derive the vacuum condition…”

“…It has been known for a while now, that one of the most promising avenues for resolving the Hubble tension in cosmology is an extra component of DE, which decays just before recombination. In the first proposal of this type, called early dark energy (EDE) [10][11][12][13][14][15], the decay of this extra component of DE happened just before recombination in a second-order rollover of an axion-like scalar field (also see [16][17][18][19][20][21][22][23][24][25][26][27][28][29][30][31][32] for related work and [33][34][35][36][37][38][39][40][41] for other early-time approaches). But without fine-tuning of the axion potential the EDE component does not dilute fast enough after the transition to be in agreement with data.…”

“…The upshot is that EDE and NEDE are equally strong phenomenological models, but differences are expected to arise with more precise CMB temperature and polarization data. In fact, first hints of these differences have already emerged in a recent ACT analysis, although it remains to be seen how much they are driven by internal inconsistencies between Planck and ACT data [15]. Beyond that, the idea of using a firstorder phase transition during the CMB epoch has led to further interesting NEDE model building efforts that, for example, consider a chain of tunneling events [25] or a confinement phase transition [26].…”