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Abstract Diverse astrophysical observations suggest the existence of cold dark matter that interacts only gravitationally with radiation and ordinary baryonic matter. Any nonzero coupling between dark matter and baryons would provide a significant step towards understanding the particle nature of dark matter. Measurements of the cosmic microwave background (CMB) provide constraints on such a coupling that complement laboratory searches. In this work we place upper limits on a variety of models for dark matter elastic scattering with protons and electrons by combining largescale CMB data from the Planck satellite with smallscale information from Atacama Cosmology Telescope (ACT) DR4 data. In the case of velocityindependent scattering, we obtain bounds on the interaction cross section for protons that are 40% tighter than previous constraints from the CMB anisotropy. For some models with velocitydependent scattering we find bestfitting cross sections with a 2 σ deviation from zero, but these scattering models are not statistically preferred over ΛCDM in terms of model selection.more » « less

Abstract We present cosmological constraints from a gravitational lensing mass map covering 9400 deg^{2}reconstructed from measurements of the cosmic microwave background (CMB) made by the Atacama Cosmology Telescope (ACT) from 2017 to 2021. In combination with measurements of baryon acoustic oscillations and big bang nucleosynthesis, we obtain the clustering amplitude
σ _{8}= 0.819 ± 0.015 at 1.8% precision, , and the Hubble constant ${S}_{8}\equiv {\sigma}_{8}{({\mathrm{\Omega}}_{\mathrm{m}}/0.3)}^{0.5}=0.840\pm 0.028$H _{0}= (68.3 ± 1.1) km s^{−1}Mpc^{−1}at 1.6% precision. A joint constraint with Planck CMB lensing yieldsσ _{8}= 0.812 ± 0.013, , and ${S}_{8}\equiv {\sigma}_{8}{({\mathrm{\Omega}}_{\mathrm{m}}/0.3)}^{0.5}=0.831\pm 0.023$H _{0}= (68.1 ± 1.0) km s^{−1}Mpc^{−1}. These measurements agree with ΛCDM extrapolations from the CMB anisotropies measured by Planck. We revisit constraints from the KiDS, DES, and HSC galaxy surveys with a uniform set of assumptions and find thatS _{8}from all three are lower than that from ACT+Planck lensing by levels ranging from 1.7σ to 2.1σ . This motivates further measurements and comparison, not just between the CMB anisotropies and galaxy lensing but also between CMB lensing probingz ∼ 0.5–5 on mostly linear scales and galaxy lensing atz ∼ 0.5 on smaller scales. We combine with CMB anisotropies to constrain extensions of ΛCDM, limiting neutrino masses to ∑m _{ν}< 0.13 eV (95% c.l.), for example. We describe the mass map and related data products that will enable a wide array of crosscorrelation science. Our results provide independent confirmation that the universe is spatially flat, conforms with general relativity, and is described remarkably well by the ΛCDM model, while paving a promising path for neutrino physics with lensing from upcoming groundbased CMB surveys. 
Abstract We present new measurements of cosmic microwave background (CMB) lensing over 9400 deg^{2}of the sky. These lensing measurements are derived from the Atacama Cosmology Telescope (ACT) Data Release 6 (DR6) CMB data set, which consists of five seasons of ACT CMB temperature and polarization observations. We determine the amplitude of the CMB lensing power spectrum at 2.3% precision (43
σ significance) using a novel pipeline that minimizes sensitivity to foregrounds and to noise properties. To ensure that our results are robust, we analyze an extensive set of null tests, consistency tests, and systematic error estimates and employ a blinded analysis framework. Our CMB lensing power spectrum measurement provides constraints on the amplitude of cosmic structure that do not depend on Planck or galaxy survey data, thus giving independent information about largescale structure growth and potential tensions in structure measurements. The baseline spectrum is well fit by a lensing amplitude ofA _{lens}= 1.013 ± 0.023 relative to the Planck 2018 CMB power spectra bestfit ΛCDM model andA _{lens}= 1.005 ± 0.023 relative to the ACT DR4 + WMAP bestfit model. From our lensing power spectrum measurement, we derive constraints on the parameter combination of ${S}_{8}^{\mathrm{CMBL}}\equiv {\sigma}_{8}{\left({\mathrm{\Omega}}_{m}/0.3\right)}^{0.25}$ from ACT DR6 CMB lensing alone and ${S}_{8}^{\mathrm{CMBL}}=0.818\pm 0.022$ when combining ACT DR6 and Planck ${S}_{8}^{\mathrm{CMBL}}=0.813\pm 0.018$NPIPE CMB lensing power spectra. These results are in excellent agreement with ΛCDM model constraints from Planck or ACT DR4 + WMAP CMB power spectrum measurements. Our lensing measurements from redshiftsz ∼ 0.5–5 are thus fully consistent with ΛCDM structure growth predictions based on CMB anisotropies probing primarilyz ∼ 1100. We find no evidence for a suppression of the amplitude of cosmic structure at low redshifts. 
Abstract We use Atacama Cosmology Telescope (ACT) observations at 98 GHz (2015–2019), 150 GHz (2013–2019), and 229 GHz (2017–2019) to perform a blind shiftandstack search for Planet 9. The search explores distances from 300 au to 2000 au and velocities up to 6.′3 per year, depending on the distance ( r ). For a 5 Earthmass Planet 9 the detection limit varies from 325 au to 625 au, depending on the sky location. For a 10 Earthmass planet the corresponding range is 425 au to 775 au. The predicted aphelion and most likely location of the planet corresponds to the shallower end of these ranges. The search covers the whole 18,000 square degrees of the ACT survey. No significant detections are found, which is used to place limits on the millimeterwave flux density of Planet 9 over much of its orbit. Overall we eliminate roughly 17% and 9% of the parameter space for a 5 and 10 Earthmass Planet 9, respectively. These bounds approach those of a recent INPOP19a ephemerisbased analysis, but do not exceed it. We also provide a list of the 10 strongest candidates from the search for possible followup. More generally, we exclude (at 95% confidence) the presence of an unknown solar system object within our survey area brighter than 4–12 mJy (depending on position) at 150 GHz with current distance 300 au < r < 600 au and heliocentric angular velocity 1 .′ 5 yr − 1 < v · 500 au r < 2 .″ 3 yr − 1 , corresponding to lowtomoderate eccentricities. These limits worsen gradually beyond 600 au, reaching 5–15 mJy by 1500 au.more » « less