article · The Astrophysical Journal
New measurements of cosmic microwave background lensing cover 9,400 square degrees of the sky using five seasons of temperature and polarisation observations from the Atacama Cosmology Telescope Data Release 6. A pipeline designed to minimise sensitivity to foregrounds and noise properties yields an amplitude of the lensing power spectrum at 2.3 percent precision, corresponding to a 43 sigma significance. The analysis relies on a blinded framework supported by extensive null tests, consistency checks, and systematic error evaluations. Because these constraints do not depend on Planck or galaxy survey data, they provide an independent test of large-scale structure growth. The measured amplitude closely matches standard cosmological predictions, yielding constraints on cosmic matter clustering that align with early universe observations. The results confirm structure growth expectations across redshifts from 0.5 to 5 with no evidence of structure suppression.
Cosmologists study whether cosmic matter has clumped together over billions of years at the rate predicted by standard physics. By providing a highly precise and independent measurement of cosmic microwave background lensing, these results confirm that large-scale cosmic structure has grown in full agreement with the standard cosmological model, helping resolve debates surrounding potential discrepancies in the expansion and clustering history of the universe.
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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 large-scale structure growth and potential tensions in structure measurements. The baseline spectrum is well fit by a lensing amplitude of A lens = 1.013 ± 0.023 relative to the Planck 2018 CMB power spectra best-fit ΛCDM model and A lens = 1.005 ± 0.023 relative to the ACT DR4 + WMAP best-fit model. From our lensing power spectrum measurement, we derive constraints on the parameter combination <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msubsup> <mml:mrow> <mml:mi>S</mml:mi> </mml:mrow> <mml:mrow> <mml:mn>8</mml:mn> </mml:mrow> <mml:mrow> <mml:mi>CMBL</mml:mi> </mml:mrow> </mml:msubsup> <mml:mo>≡</mml:mo> <mml:msub> <mml:mrow> <mml:mi>σ</mml:mi> </mml:mrow> <mml:mrow> <mml:mn>8</mml:mn> </mml:mrow> </mml:msub> <mml:msup> <mml:mrow> <mml:mfenced close=")" open="("> <mml:mrow> <mml:msub> <mml:mrow> <mml:mi mathvariant="normal">Ω</mml:mi> </mml:mrow> <mml:mrow> <mml:mi>m</mml:mi> </mml:mrow> </mml:msub> <mml:mrow> <mml:mo stretchy="true">/</mml:mo> </mml:mrow> <mml:mn>0.3</mml:mn> </mml:mrow> </mml:mfenced> </mml:mrow> <mml:mrow> <mml:mn>0.25</mml:mn> </mml:mrow> </mml:msup> </mml:math> of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msubsup> <mml:mrow> <mml:mi>S</mml:mi> </mml:mrow> <mml:mrow> <mml:mn>8</mml:mn> </mml:mrow> <mml:mrow> <mml:mi>CMBL</mml:mi> </mml:mrow> </mml:msubsup> <mml:mo>=</mml:mo> <mml:mn>0.818</mml:mn> <mml:mo>±</mml:mo> <mml:mn>0.022</mml:mn> </mml:math> from ACT DR6 CMB lensing alone and <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msubsup> <mml:mrow> <mml:mi>S</mml:mi> </mml:mrow> <mml:mrow> <mml:mn>8</mml:mn> </mml:mrow> <mml:mrow> <mml:mi>CMBL</mml:mi> </mml:mrow> </mml:msubsup> <mml:mo>=</mml:mo> <mml:mn>0.813</mml:mn> <mml:mo>±</mml:mo> <mml:mn>0.018</mml:mn> </mml:math> when combining ACT DR6 and Planck 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 redshifts z ∼ 0.5–5 are thus fully consistent with ΛCDM structure growth predictions based on CMB anisotropies probing primarily z ∼ 1100. We find no evidence for a suppression of the amplitude of cosmic structure at low redshifts.
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DOI: 10.3847/1538-4357/acfe06
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