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Towards constraining cosmological parameters with SPT-3G observations of 25% of the sky

A. Vitrier ^1,*, K. Fichman^2,3,4, L. Balkenhol¹, E. Camphuis¹, F. Guidi^5,1, A. R. Khalife¹, A. J. Anderson^6,3,7, B. Ansarinejad⁸, M. Archipley^7,3 et al. (SPT-3G Collaboration)

M. Archipley^7,3, D. R. Barron⁹, K. Benabed¹, A. N. Bender^4,3,7, B. A. Benson^6,3,7, F. Bianchini^10,11,12, L. E. Bleem^4,3,7, S. Bocquet¹³, F. R. Bouchet¹, L. Bryant¹⁴, M. G. Campitiello⁴, J. E. Carlstrom^3,14,2,4,7, J. Carron^15,16, C. L. Chang^4,3,7, P. Chaubal⁸, P. M. Chichura^2,3, A. Chokshi⁷, T.-L. Chou^7,3,17, A. Coerver¹⁸, T. M. Crawford^7,3, C. Daley^19,20, T. de Haan²¹, K. R. Dibert^7,3, M. A. Dobbs^22,23, M. Doohan⁸, A. Doussot¹, D. Dutcher²⁴, W. Everett²⁵, C. Feng^26,27,28, K. R. Ferguson^29,30, N. C. Ferree^31,10,11, A. Foster²⁴, S. Galli¹, A. E. Gambrel³, A. K. Gao²⁸, R. W. Gardner¹⁴, F. Ge^31,10,11,5, N. Goeckner-Wald^11,10, R. Gualtieri^4,32, S. Guns¹⁸, N. W. Halverson^33,34, E. Hivon¹, A. Y. Q. Ho³⁵, G. P. Holder²⁸, W. L. Holzapfel¹⁸, J. C. Hood³, A. Hryciuk^2,3, N. Huang¹⁸, T. Jhaveri^7,3, F. Kéruzoré⁴, L. Knox⁵, M. Korman³⁶, K. Kornoelje^7,3,4, C.-L. Kuo^10,11,12, K. Levy⁸, Y. Li³, A. E. Lowitz³, C. Lu²⁸, G. P. Lynch⁵, T. J. Maccarone³⁷, A. S. Maniyar^10,11,12, E. S. Martsen^7,3, F. Menanteau^20,38, M. Millea¹⁸, J. Montgomery²², Y. Nakato¹¹, T. Natoli³, G. I. Noble^39,40, Y. Omori^7,3, A. Ouellette²⁸, Z. Pan^4,3,2, P. Paschos¹⁴, K. A. Phadke^20,38,41, A. W. Pollak⁷, K. Prabhu⁵, W. Quan^4,2,3, M. Rahimi⁸, A. Rahlin^7,3, C. L. Reichardt⁸, M. Rouble²², J. E. Ruhl³⁶, E. Schiappucci⁸, A. C. Silva Oliveira^31,10,11, A. Simpson^7,3, J. A. Sobrin^6,3, A. A. Stark⁴², J. Stephen¹⁴, C. Tandoi²⁰, B. Thorne⁵, C. Trendafilova³⁸, C. Umilta²⁸, J. D. Vieira^20,28,38, A. G. Vieregg^3,7,14,2, Y. Wan^20,38, N. Whitehorn³⁰, W. L. K. Wu^31,10,12, M. R. Young^6,3, and J. A. Zebrowski^3,7,6 (SPT-3G Collaboration)

¹Sorbonne Université, CNRS, UMR 7095, Institut d’Astrophysique de Paris, 98 bis bd Arago, 75014 Paris, France
²Department of Physics, University of Chicago, 5640 South Ellis Avenue, Chicago, Illinois 60637, USA
³Kavli Institute for Cosmological Physics, University of Chicago, 5640 South Ellis Avenue, Chicago, Illinois 60637, USA
⁴High-Energy Physics Division, Argonne National Laboratory, 9700 South Cass Avenue, Lemont, Illinois 60439, USA
⁵Department of Physics and Astronomy, University of California, One Shields Avenue, Davis, California 95616, USA
⁶Fermi National Accelerator Laboratory, MS209, P.O. Box 500, Batavia, Illinois 60510, USA
⁷Department of Astronomy and Astrophysics, University of Chicago, 5640 South Ellis Avenue, Chicago, Illinois 60637, USA
⁸School of Physics, University of Melbourne, Parkville, VIC 3010, Australia
⁹Department of Physics and Astronomy, University of New Mexico, Albuquerque, New Mexico 87131, USA
¹⁰Kavli Institute for Particle Astrophysics and Cosmology, Stanford University, 452 Lomita Mall, Stanford, California 94305, USA
¹¹Department of Physics, Stanford University, 382 Via Pueblo Mall, Stanford, California 94305, USA
¹²SLAC National Accelerator Laboratory, 2575 Sand Hill Road, Menlo Park, California 94025, USA
¹³University Observatory, Faculty of Physics, Ludwig-Maximilians-Universität, Scheinerstr. 1, 81679 Munich, Germany
¹⁴Enrico Fermi Institute, University of Chicago, 5640 South Ellis Avenue, Chicago, Illinois 60637, USA
¹⁵Université de Genève, Département de Physique Théorique, 24 Quai Ansermet, CH-1211 Genève 4, Switzerland
¹⁶Department of Physics and Astronomy, University of Sussex, Brighton BN1 9QH, United Kingdom
¹⁷National Taiwan University, No. 1, Sec.IV, Roosevelt Road, Taipei 106319, Taiwan
¹⁸Department of Physics, University of California, Berkeley, California 94720, USA
¹⁹Université Paris-Saclay, Université Paris Cité, CEA, CNRS, AIM, 91191, Gif-sur-Yvette, France
²⁰Department of Astronomy, University of Illinois Urbana-Champaign, 1002 West Green Street, Urbana, Illinois 61801, USA
²¹High Energy Accelerator Research Organization (KEK), Tsukuba, Ibaraki 305-0801, Japan
²²Department of Physics and McGill Space Institute, McGill University, 3600 Rue University, Montreal, Quebec H3A 2T8, Canada
²³Canadian Institute for Advanced Research, CIFAR Program in Gravity and the Extreme Universe, Toronto, Ontario M5G 1Z8, Canada
²⁴Joseph Henry Laboratories of Physics, Jadwin Hall, Princeton University, Princeton, New Jersey 08544, USA
²⁵Department of Astrophysical and Planetary Sciences, University of Colorado, Boulder, Colorado 80309, USA
²⁶Department of Astronomy, University of Science and Technology of China, Hefei 230026, China
²⁷School of Astronomy and Space Science, University of Science and Technology of China, Hefei 230026, China
²⁸Department of Physics, University of Illinois Urbana-Champaign, 1110 West Green Street, Urbana, Illinois 61801, USA
²⁹Department of Physics and Astronomy, University of California, Los Angeles, California 90095, USA
³⁰Department of Physics and Astronomy, Michigan State University, East Lansing, Michigan 48824, USA
³¹California Institute of Technology, 1200 East California Boulevard., Pasadena, California, 91125, USA
³²Department of Physics and Astronomy, Northwestern University, 633 Clark St, Evanston, Illinois 60208, USA
³³CASA, Department of Astrophysical and Planetary Sciences, University of Colorado, Boulder, Colorado 80309, USA
³⁴Department of Physics, University of Colorado, Boulder, Colorado 80309, USA
³⁵Department of Astronomy, Cornell University, Ithaca, New York 14853, USA
³⁶Department of Physics, Case Western Reserve University, Cleveland, Ohio 44106, USA
³⁷Department of Physics and Astronomy, Box 41051, Texas Tech University, Lubbock Texas 79409-1051, USA
³⁸Center for AstroPhysical Surveys, National Center for Supercomputing Applications, Urbana, Illinois 61801, USA
³⁹Dunlap Institute for Astronomy and Astrophysics, University of Toronto, 50 St. George Street, Toronto, Ontario, M5S 3H4, Canada
⁴⁰David A. Dunlap Department of Astronomy and Astrophysics, University of Toronto, 50 St. George Street, Toronto, Ontario, M5S 3H4, Canada
⁴¹NSF-Simons AI Institute for the Sky (SkAI), 172 East Chestnut Street, Chicago, Illinois 60611, USA
⁴²Center for Astrophysics/Harvard and Smithsonian, 60 Garden Street, Cambridge, Massachusetts 02138, USA

^*Contact author: vitrier@iap.fr

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Phys. Rev. D 114, 043548 – Published 25 August, 2026

DOI: https://doi.org/10.1103/8yfb-t1j9

Abstract

The South Pole Telescope (SPT), using its third-generation camera, SPT-3G, is conducting observations of the cosmic microwave background (CMB) in temperature and polarization across approximately $10 000 \deg^{2}$ of the sky at 95, 150, and 220 GHz. This comprehensive dataset should yield stringent constraints on cosmological parameters. In this work, we explore its potential to address the Hubble tension by forecasting constraints from temperature, polarization, and CMB lensing on early dark energy (EDE) and the variation in electron mass in spatially flat and curved universes. For this purpose, we investigate first whether analyzing the distinct SPT-3G observation fields independently, as opposed to as a single, unified region, results in a loss of information relevant to cosmological parameter estimation. We develop a realistic temperature and polarization likelihood pipeline capable of analyzing these fields in these two ways, and subsequently forecast constraints on cosmological parameters. Our findings indicate that any loss of constraining power from analyzing the fields separately is primarily concentrated at low multipoles ( $ℓ < 50$ ) and the overall impact on the relative uncertainty on standard $Λ$ cold dark matter parameters is minimal ( $< 3 %$ ). Our forecasts suggest that SPT-3G data should improve by more than a factor of 90 and 190 the figure of merit of the EDE and the varying electron mass models, respectively, when combined with Planck data. The likelihood pipeline developed and used in this work is made publicly available online.

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Towards constraining cosmological parameters with SPT-3G observations of 25% of the sky

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