Atacama Cosmology Telescope: Constraints on prerecombination early dark energy

The early dark energy (EDE) scenario aims to increase the value of Hubble constant (H0) inferred from cosmic microwave background (CMB) data over that found in standard cosmological model (ΛCDM), via introduction a new form density Universe. EDE component briefly accelerates expansion just prior recombination, which reduces physical size sound horizon imprinted CMB. Previous work has nonzero is not preferred by Planck CMB power spectrum alone, yield 95% confidence level (C.L.) upper limit fEDE<0.087 on maximal fractional contribution field budget. In this paper, we fit Atacama Cosmology Telescope (ACT) release 4. We find combination ACT, large-scale TT (similar WMAP), lensing, and BAO prefers existence at >99.7% C.L.: fEDE=0.091−0.036+0.020, with H0=70.9−2.0+1.0 km/s/Mpc (both 68% C.L.). From model-selection standpoint, favored ΛCDM these roughly 3σ significance. contrast, joint analysis full ACT yields no evidence for EDE, as previously alone. show preference alone driven its TE EE data. tight constraint high-ℓ Understanding whether differing constraints are nature, due systematics, or simply rare statistical fluctuation high priority. best-fit models exhibit coherent differences across wide range multipoles EE, indicating powerful test anticipated near-future other ground-based experiments.18 MoreReceived 14 September 2021Accepted June 2022DOI:https://doi.org/10.1103/PhysRevD.105.123536© 2022 American Physical SocietyPhysics Subject Headings (PhySH)Research AreasCosmic backgroundCosmological parametersDark energyEvolution UniverseGravitation, & Astrophysics