The Atacama Cosmology Telescope: Constraints on Pre-Recombination Early Dark Energy
Creators: name: Hill, J. Colin
name: Calabrese, Erminia
name: Aiola, Simone
name: Battaglia, Nicholas
name: Bolliet, Boris
name: Choi, Steve K.
name: Devlin, Mark J.
name: Duivenvoorden, Adriaan J.
name: Dunkley, Jo
name: Ferraro, Simone
name: Gallardo, Patricio A.
name: Gluscevic, Vera
name: Hasselfield, Matthew
name: Hilton, Matt
name: Hincks, Adam D.
name: Hlozek, Renee
name: Koopman, Brian J.
name: Kosowsky, Arthur
name: La Posta, Adrien
name: Louis, Thibaut
name: Madhavacheril, Mathew S.
name: McMahon, Jeff
name: Moodley, Kavilan
name: Naess, Sigurd
name: Natale, Umberto
name: Nati, Federico
name: Newburgh, Laura
name: Niemack, Michael D.
name: Page, Lyman A.
name: Partridge, Bruce
name: Qu, Frank J.
name: Salatino, Maria
name: Schillaci, Alessandro
name: Sehgal, Neelima
name: Sherwin, Blake D.
name: Sifon, Cristobal
name: Spergel, David N.
name: Staggs, Suzanne T.
name: Storer, Emilie R.
name: van Engelen, Alexander
name: Vavagiakis, Eve M.
name: Wollack, Edward J.
name: Xu, Zhilei
Publisher: name: arXiv
Year: 2021
Subjects: subject: Cosmology and Nongalactic Astrophysics (astro-ph.CO)
subject: General Relativity and Quantum Cosmology (gr-qc)
subject: High Energy Physics - Phenomenology (hep-ph)
subject: FOS: Physical sciences
subject: FOS: Physical sciences

description: The early dark energy (EDE) scenario aims to increase the value of the Hubble constant ($H_0$) inferred from cosmic microwave background (CMB) data over that found in $Λ$CDM, via the introduction of a new form of energy density in the early universe. The EDE component briefly accelerates cosmic expansion just prior to recombination, which reduces the physical size of the sound horizon imprinted in the CMB. Previous work has found that non-zero EDE is not preferred by Planck CMB power spectrum data alone, which yield a 95% confidence level (CL) upper limit $f_{\rm EDE} &lt; 0.087$ on the maximal fractional contribution of the EDE field to the cosmic energy budget. In this paper, we fit the EDE model to CMB data from the Atacama Cosmology Telescope (ACT) Data Release 4. We find that a combination of ACT, large-scale Planck TT (similar to WMAP), Planck CMB lensing, and BAO data prefers the existence of EDE at $&gt;99.7$% CL: $f_{\rm EDE} = 0.091^{+0.020}_{-0.036}$, with $H_0 = 70.9^{+1.0}_{-2.0}$ km/s/Mpc (both 68% CL). From a model-selection standpoint, we find that EDE is favored over $Λ$CDM by these data at roughly $3σ$ significance. In contrast, a joint analysis of the full Planck and ACT data yields no evidence for EDE, as previously found for Planck alone. We show that the preference for EDE in ACT alone is driven by its TE and EE power spectrum data. The tight constraint on EDE from Planck alone is driven by its high-$\ell$ TT power spectrum data. Understanding whether these differing constraints are physical in nature, due to systematics, or simply a rare statistical fluctuation is of high priority. The best-fit EDE models to ACT and Planck exhibit coherent differences across a wide range of multipoles in TE and EE, indicating that a powerful test of this scenario is anticipated with near-future data from ACT and other ground-based experiments.
description: v1: 25+20 pages, 6+18 figures, submitted to PRD; v2: 26+20 pages, 7+18 figures, results unchanged, matches PRD accepted version. MCMC chains available at https://lambda.gsfc.nasa.gov/product/act/actpol_mcmc_chains_get.html