KiDS-Legacy: Constraining dark energy, neutrino mass, and curvature

¹ Argelander-Institut für Astronomie, Universität Bonn, Auf dem Hügel 71, D-53121 Bonn, Germany
² Ruhr University Bochum, Faculty of Physics and Astronomy, Astronomical Institute (AIRUB), German Centre for Cosmological Lensing, 44780 Bochum, Germany
³ Department of Physics and Astronomy, University College London, Gower Street, London WC1E 6BT, United Kingdom
⁴ School of Mathematics, Statistics and Physics, Newcastle University, Herschel Building, NE1 7RU, Newcastle-upon-Tyne, United Kingdom
⁵ Center for Theoretical Physics, Polish Academy of Sciences, al. Lotników 32/46, 02-668 Warsaw, Poland
⁶ Institute for Theoretical Physics, Utrecht University, Princetonplein 5, 3584 CC, Utrecht, The Netherlands
⁷ Leiden Observatory, Leiden University, P.O. Box 9513, 2300 RA, Leiden, The Netherlands
⁸ Institut de Física d’Altes Energies (IFAE), The Barcelona Institute of Science and Technology, Campus UAB, 08193 Bellaterra (Barcelona), Spain
⁹ Institute for Astronomy, University of Edinburgh, Royal Observatory, Blackford Hill, Edinburgh EH9 3HJ, United Kingdom
¹⁰ Centro de Investigaciones Energéticas, Medioambientales y Tecnológicas (CIEMAT), Av. Complutense 40, E-28040, Madrid, Spain
¹¹ Kavli Institute for Particle Astrophysics and Cosmology, Stanford University, Stanford, CA 94305, USA
¹² SLAC National Accelerator Laboratory, Menlo Park, CA 94025, USA
¹³ Universität Innsbruck, Institut für Astro- und Teilchenphysik, Technikerstr. 25/8, 6020 Innsbruck, Austria
¹⁴ The Oskar Klein Centre, Department of Physics, Stockholm University, AlbaNova University Centre, SE-106 91 Stockholm, Sweden
¹⁵ Imperial Centre for Inference and Cosmology (ICIC), Blackett Laboratory, Imperial College London, Prince Consort Road, London SW7 2AZ, United Kingdom
¹⁶ Department of Physics, University of Oxford, Denys Wilkinson Building, Keble Road, Oxford OX1 3RH, United Kingdom
¹⁷ Donostia International Physics Center, Manuel Lardizabal Ibilbidea, 4, 20018 Donostia, Gipuzkoa, Spain
¹⁸ Dipartimento di Fisica e Astronomia “Augusto Righi” – Alma Mater Studiorum Università di Bologna, Via Piero Gobetti 93/2, I-40129 Bologna, Italy
¹⁹ Istituto Nazionale di Astrofisica (INAF) – Osservatorio di Astrofisica e Scienza dello Spazio (OAS), Via Piero Gobetti 93/3, I-40129 Bologna, Italy
²⁰ Istituto Nazionale di Fisica Nucleare (INFN) – Sezione di Bologna, Viale Berti Pichat 6/2, I-40127 Bologna, Italy
²¹ Department of Physics “E. Pancini” University of Naples Federico II C.U. di Monte Sant’Angelo Via Cintia, 21 ed. 6, 80126 Naples, Italy
²² INAF – Osservatorio Astronomico di Padova, Via dell’Osservatorio 5, 35122 Padova, Italy
²³ Institute for Particle Physics and Astrophysics, ETH Zürich, Wolfgang-Pauli-Strasse 27, 8093 Zürich, Switzerland
²⁴ Institute for Computational Cosmology, Ogden Centre for Fundamental Physics – West, Department of Physics, Durham University, South Road, Durham DH1 3LE, United Kingdom
²⁵ Centre for Extragalactic Astronomy, Ogden Centre for Fundamental Physics – West, Department of Physics, Durham University, South Road, Durham DH1 3LE, United Kingdom
²⁶ Graduate School of Science, Nagoya University, Furocho, Chikusa-ku, Nagoya, Aichi 464-8602, Japan

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Received: 15 December 2025
Accepted: 17 March 2026

Abstract

We constrained minimally extended cosmological models with the cosmic shear analysis of the final data release from the Kilo-Degree Survey (KiDS-Legacy) in combination with external probes. Due to the consistency of the KiDS-Legacy analysis with the cosmic microwave background (CMB), we could combine these datasets reliably for the first time. Additionally, we used CMB lensing, galaxy redshift-space distortions, and baryon acoustic oscillations. We assessed, in turn, the effects of spatial curvature, varying neutrino masses, and an evolving dark energy component on cosmological constraints from KiDS-Legacy alone and from KiDS-Legacy combined with external probes. We find KiDS-Legacy to be consistent with the fiducial flat Λ-cold dark matter (ΛCDM) analysis with c²∑m_ν ≤ 1.5 eV, w₀ = −1.0 ± 0.7, and w_a = −1.3_−2.0^+1.9 while Ω_K = 0.8_−0.17^+0.16 (1σ bounds) with an almost equal goodness of fit. The w₀w_aCDM model is not a significant improvement over ΛCDM when cosmic shear and CMB lensing are combined, yielding a Bayes factor B = 0.07. If all probes are combined, however, B increases to 2.73, corresponding to a 2.6σ suspiciousness tension. The constraint on S₈ = σ₈√Ω_m/0.3 is robust to opening up the parameter space for cosmic shear. Adding all external datasets to KiDS-Legacy, we find S₈ = 0.816 ± 0.006 in ΛCDM and S₈ = 0.837 ± 0.008 in w₀w_aCDM for all probes combined.