We present power spectra of the cosmic microwave background (CMB) anisotropy in temperature and polarization, measured from the Data Release 6 maps made from Atacama Cosmology Telescope (ACT) data. These cover 19, 000 deg² of sky in bands centered at 98, 150 and 220 GHz, with white noise levels three times lower than Planck in polarization. We find that the ACT angular power spectra estimated over 10, 000 deg², and measured to arcminute scales in TT, TE and EE, are well fit by the sum of CMB and foregrounds, where the CMB spectra are described by the ΛCDM model. Combining ACT with larger-scale Planck data, the joint P-ACT dataset provides tight limits on the ingredients, expansion rate, and initial conditions of the universe. We find similar constraining power, and consistent results, from either the Planck power spectra or from ACT combined with WMAP data, as well as from either temperature or polarization in the joint P-ACT dataset. When combined with CMB lensing from ACT and Planck, and baryon acoustic oscillation data from DESI DR1, we measure a baryon density of Ωb h²=0. 02260. 0001, a cold dark matter density of Ωc h²=0. 1180. 001, a Hubble constant of H₀=68. 220. 36 km/s/Mpc, a spectral index of nₛ=0. 9740. 003, and an amplitude of density fluctuations of σ₈=0. 8130. 005. Including the DESI DR2 data tightens the Hubble constant to H₀=68. 430. 27 km/s/Mpc; ΛCDM parameters agree between the P-ACT and DESI DR2 data at the 1. 6σ level. We find no evidence for excess lensing in the power spectrum, and no departure from spatial flatness. The contribution from Sunyaev-Zel'dovich (SZ) anisotropy is detected at high significance; we find evidence for a tilt with suppressed small-scale power compared to our baseline SZ template spectrum, consistent with hydrodynamical simulations with feedback.
Louis et al. (Tue,) studied this question.