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

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_νłeq 1. 5, eV, w₀ = -1. 0± 0. 7, and wₐ = +1. 9 _ -2. 0 while ΩK = 0. 08^ +0. 16 _ -0. 17 (1σ bounds) with an almost equal goodness of fit. The w₀wₐCDM 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 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 w₀ wₐCDM for all probes combined. Ω_ /0. 3 m