The Atacama Cosmology Telescope: DR6 constraints on extended cosmological models

Calabrese, Erminia ORCID: https://orcid.org/0000-0003-0837-0068, Hill, J. Colin, Jense, Hidde T., La Posta, Adrien, Abril-Cabezas, Irene, Addison, Graeme E., Ade, Peter A.R. ORCID: https://orcid.org/0000-0002-5127-0401, Aiola, Simone, Alford, Tommy, Alonso, David, Amiri, Mandana, An, Rui, Atkins, Zachary, Austermann, Jason E., Barbavara, Eleonora, Barbieri, Nicola, Battaglia, Nicholas, Battistelli, Elia Stefano, Beall, James A., Bean, Rachel, Beheshti, Ali, Beringue, Benjamin, Bhandarkar, Tanay, Biermann, Emily, Bolliet, Boris, Bond, J Richard, Capalbo, Valentina, Carrero, Felipe, Chen, Shi-Fan, Chesmore, Grace, Cho, Hsiao-mei, Choi, Steve K., Clark, Susan E., Cothard, Nicholas F., Coughlin, Kevin, Coulton, William, Crichton, Devin, Crowley, Kevin T., Darwish, Omar, Devlin, Mark J., Dicker, Simon, Duell, Cody J., Duff, Shannon M., Duivenvoorden, Adriaan J., Dunkley, Jo, Dunner, Rolando, Embil Villagra, Carmen, Fankhanel, Max, Farren, Gerrit S., Ferraro, Simone, Foster, Allen, Freundt, Rodrigo, Fuzia, Brittany, Gallardo, Patricio A., Garrido, Xavier, Gerbino, Martina, Giardiello, Serena, Gill, Ajay, Givans, Jahmour, Gluscevic, Vera, Goldstein, Samuel, Golec, Joseph E., Gong, Yulin, Guan, Yilun, Halpern, Mark, Harrison, Ian ORCID: https://orcid.org/0000-0002-4437-0770, Hasselfield, Matthew, He, Adam, Healy, Erin, Henderson, Shawn, Hensley, Brandon, Hervías-Caimapo, Carlos, Hilton, Gene C., Hilton, Matt, Hincks, Adam D., Hložek, Renée, Ho, Shuay-Pwu Patty, Hood, John, Hornecker, Erika, Huber, Zachary B., Hubmayr, Johannes, Huffenberger, Kevin M., Hughes, John P., Ikape, Margaret, Irwin, Kent, Isopi, Giovanni, Joshi, Neha, Keller, Ben, Kim, Joshua, Knowles, Kenda, Koopman, Brian J., Kosowsky, Arthur, Kramer, Darby, Kusiak, Aleksandra, Laguë, Alex, Lakey, Victoria, Lattanzi, Massimiliano, Lee, Eunseong, Li, Yaqiong, Li, Zack, Limon, Michele, Lokken, Martine, Louis, Thibaut, Lungu, Marius, MacCrann, Niall, MacInnis, Amanda, Madhavacheril, Mathew S., Maldonado, Diego, Maldonado, Felipe, Mallaby-Kay, Maya, Marques, Gabriela A., van Marrewijk, Joshiwa, McCarthy, Fiona, McMahon, Jeff, Mehta, Yogesh, Menanteau, Felipe, Moodley, Kavilan, Morris, Thomas W., Mroczkowski, Tony, Naess, Sigurd, Namikawa, Toshiya, Nati, Federico, Nerval, Simran K., Newburgh, Laura, Nicola, Andrina, Niemack, Michael D., Nolta, Michael R., Orlowski-Scherer, John, Pagano, Luca, Page, Lyman A., Pandey, Shivam, Partridge, Bruce, Perez Sarmiento, Karen, Prince, Heather, Puddu, Roberto, Qu, Frank J., Ragavan, Damien C., Ried Guachalla, Bernardita, Rogers, Keir K., Rojas, Felipe, Sakuma, Tai, Schaan, Emmanuel, Schmitt, Benjamin L., Sehgal, Neelima, Shaikh, Shabbir, Sherwin, Blake D., Sierra, Carlos, Sievers, Jon, Sifón, Cristóbal, Simon, Sara, Sonka, Rita, Spergel, David N., Staggs, Suzanne T., Storer, Emilie, Surrao, Kristen, Switzer, Eric R., Tampier, Niklas, Thiele, Leander, Thornton, Robert, Trac, Hy, Tucker, Carole ORCID: https://orcid.org/0000-0002-1851-3918, Ullom, Joel, Vale, Leila R., Van Engelen, Alexander, Van Lanen, Jeff, Vargas, Cristian, Vavagiakis, Eve M., Wagoner, Kasey, Wang, Yuhan, Wenzl, Lukas, Wollack, Edward J., Zheng, Kaiwen and The Atacama Cosmology Telescope collaboration, . 2025. The Atacama Cosmology Telescope: DR6 constraints on extended cosmological models. Journal of Cosmology and Astroparticle Physics 2025 (11) , 063. 10.1088/1475-7516/2025/11/063

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Abstract

We use new cosmic microwave background (CMB) primary temperature and polarization anisotropy measurements from the Atacama Cosmology Telescope (ACT) Data Release 6 (DR6) to test foundational assumptions of the standard cosmological model, ΛCDM, and set constraints on extensions to it. We derive constraints from the ACT DR6 power spectra alone, as well as in combination with legacy data from the Planck mission. To break geometric degeneracies, we include ACT and Planck CMB lensing data and baryon acoustic oscillation data from DESI Year-1. To test the dependence of our results on non-ACT data, we also explore combinations replacing Planck with WMAP and DESI with BOSS, and further add supernovae measurements from Pantheon+ for models that affect the late-time expansion history. We verify the near-scale-invariance (running of the spectral index dns /d ln k = 0.0062 ± 0.0052) and adiabaticity of the primordial perturbations. Neutrino properties are consistent with Standard Model predictions: we find no evidence for new light, relativistic species that are free-streaming (N eff = 2.86 ± 0.13, which combined with astrophysical measurements of primordial helium and deuterium abundances becomes N eff = 2.89 ± 0.11), for non-zero neutrino masses (∑mν < 0.089 eV at 95% CL), or for neutrino self-interactions. We also find no evidence for self-interacting dark radiation (N idr < 0.134), or for early-universe variation of fundamental constants, including the fine-structure constant (α EM/α EM,0 = 1.0043 ± 0.0017) and the electron mass (me /me,0 = 1.0063 ± 0.0056). Our data are consistent with standard big bang nucleosynthesis (we find Yp = 0.2312 ± 0.0092), the COBE/FIRAS-inferred CMB temperature (we find T CMB = 2.698 ± 0.016 K), a dark matter component that is collisionless and with only a small fraction allowed as axion-like particles, a cosmological constant (w = -0.986 ± 0.025), and the late-time growth rate predicted by general relativity (γ = 0.663 ± 0.052). We find no statistically significant preference for a departure from the baseline ΛCDM model. In fits to models invoking early dark energy, primordial magnetic fields, or an arbitrary modified recombination history, we find H 0 = 69.9+0.8 -1.5, 69.1 ± 0.5, or 69.6 ± 1.0 km/s/Mpc, respectively; using BOSS instead of DESI BAO data reduces the central values of these constraints by 1–1.5 km/s/Mpc while only slightly increasing the error bars. In general, models introduced to increase the Hubble constant or to decrease the amplitude of density fluctuations inferred from the primary CMB are not favored over ΛCDM by our data.

Item Type:	Article
Date Type:	Published Online
Status:	Published
Schools:	Schools > Physics and Astronomy
Additional Information:	License information from Publisher: LICENSE 1: URL: http://creativecommons.org/licenses/by/4.0/, Type: cc-by
Publisher:	IOP Publishing
Date of First Compliant Deposit:	27 November 2025
Date of Acceptance:	21 June 2025
Last Modified:	27 Nov 2025 11:27
URI:	https://orca.cardiff.ac.uk/id/eprint/182702

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