The Atacama Cosmology Telescope: A Measurement of the DR6 CMB Lensing Power Spectrum and Its Implications for Structure Growth
Authors: Qu Frank J. , Sherwin Blake D. , Madhavacheril Mathew S. , Han Dongwon , Crowley Kevin T. , Abril-Cabezas Irene , Ade Peter A. R. , Aiola Simone , Alford Tommy , Amiri Mandana , Amodeo Stefania , An Rui , Atkins Zachary , Austermann Jason E. , Battaglia Nicholas , Battistelli Elia Stefano , Beall James A. , Bean Rachel , Beringue Benjamin , Bhandarkar Tanay , Biermann Emily , Bolliet Boris , Bond J Richard , Cai Hongbo , Calabrese Erminia , Calafut Victoria , Capalbo Valentina , Carrero Felipe , Carron Julien , Challinor Anthony , Chesmore Grace E. , Cho Hsiao-mei , Choi Steve K. , Clark Susan E. , Córdova Rosado Rodrigo , Cothard Nicholas F. , Coughlin Kevin , Coulton William , Dalal Roohi , Darwish Omar , Devlin Mark J. , Dicker Simon , Doze Peter , Duell Cody J. , Duff Shannon M. , Duivenvoorden Adriaan J. , Dunkley Jo , Dünner Rolando , Fanfani Valentina , Fankhanel Max , Farren Gerrit , Ferraro Simone , Freundt Rodrigo , Fuzia Brittany , Gallardo Patricio A. , Garrido Xavier , Gluscevic Vera , Golec Joseph E. , Guan Yilun , Halpern Mark , Harrison Ian , Hasselfield Matthew , Healy Erin , Henderson Shawn , Hensley Brandon , Hervías-Caimapo Carlos , Hill J. Colin , Hilton Gene C. , Hilton Matt , Hincks Adam D. , Hložek Renée , Ho Shuay-Pwu Patty , Huber Zachary B. , Hubmayr Johannes , Huffenberger Kevin M. , Hughes John P. , Irwin Kent , Isopi Giovanni , Jense Hidde T. , Keller Ben , Kim Joshua , Knowles Kenda , Koopman Brian J. , Kosowsky Arthur , Kramer Darby , Kusiak Aleksandra , La Posta Adrien , Lague Alex , Lakey Victoria , Lee Eunseong , Li Zack , Li Yaqiong , Limon Michele , Lokken Martine , Louis Thibaut , Lungu Marius , MacCrann Niall , MacInnis Amanda , Maldonado Diego , Maldonado Felipe , Mallaby-Kay Maya , Marques Gabriela A. , McMahon Jeff , Mehta Yogesh , Menanteau Felipe , Moodley Kavilan , Morris Thomas W. , Mroczkowski Tony , Naess Sigurd , Namikawa Toshiya , Nati Federico , Newburgh Laura , Nicola Andrina , Niemack Michael D. , Nolta Michael R. , Orlowski-Scherer John , Page Lyman A. , Pandey Shivam , Partridge Bruce , Prince Heather , Puddu Roberto , Radiconi Federico , Robertson Naomi , Rojas Felipe , Sakuma Tai , Salatino Maria , Schaan Emmanuel , Schmitt Benjamin L. , Sehgal Neelima , Shaikh Shabbir , Sierra Carlos , Sievers Jon , Sifón Cristóbal , Simon Sara , Sonka Rita , Spergel David N. , Staggs Suzanne T. , Storer Emilie , Switzer Eric R. , Tampier Niklas , Thornton Robert , Trac Hy , Treu Jesse , Tucker Carole , Ullom Joel , Vale Leila R. , Van Engelen Alexander , Van Lanen Jeff , van Marrewijk Joshiwa , Vargas Cristian , Vavagiakis Eve M. , Wagoner Kasey , Wang Yuhan , Wenzl Lukas , Wollack Edward J. , Xu Zhilei , Zago Fernando , Zheng Kaiwen 
Published: February 2024

Abstract
We present new measurements of cosmic microwave background (CMB) lensing over 9400 deg2 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 (43σ 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

S

8

CMBL

≡

σ

8

Ω

m

/

0.3

0.25

of

S

8

CMBL

=
0.818
±
0.022

from ACT DR6 CMB lensing alone and

S

8

CMBL

=
0.813
±
0.018

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.