KiDS-1000 Cosmology: Constraints beyond flat ΛCDM

We present constraints on extensions to the standard cosmological model of a spatially flat Universe governed by general relativity, a cosmological constant (Lambda), and cold dark matter (CDM) by varying the spatial curvature Omega (K), the sum of the neutrino masses Sigma m(nu), the dark energy equation of state parameter w, and the Hu-Sawicki f(R) gravity f(R0) parameter. With the combined 3x2 pt measurements of cosmic shear from the Kilo-Degree Survey (KiDS-1000), galaxy clustering from the Baryon Oscillation Spectroscopic Survey (BOSS), and galaxy-galaxy lensing from the overlap between KiDS-1000, BOSS, and the spectroscopic 2-degree Field Lensing Survey, we find results that are fully consistent with a flat Lambda CDM model with Omega (K) = 0.011(-0.057)(+0.054) Omega K = 0 . 011 - 0.057 + 0.054 Sigma ,Sigma m(nu)<1.76 eV (95% CL), and w = -0.99(-0.13)(+0.11) w = - 0 . 99 - 0.13 + 0.11 text . The f(R0) parameter is unconstrained in our fully non-linear f(R) cosmic shear analysis. Considering three different model selection criteria, we find no clear preference for either the fiducial flat Lambda CDM model or any of the considered extensions. In addition to extensions to the flat Lambda CDM parameter space, we also explore restrictions to common subsets of the flat Lambda CDM parameter space by fixing the amplitude of the primordial power spectrum to the Planck best-fit value, as well as adding external data from supernovae and lensing of the cosmic microwave background (CMB). Neither the beyond-Lambda CDM models nor the imposed restrictions explored in this analysis are able to resolve the similar to 3 sigma tension in S-8 between the 3x2 pt constraints and the Planck temperature and polarisation data, with the exception of wCDM, where the S-8 tension is resolved. The tension in the wCDM case persists, however, when considering the joint S-8-w parameter space. The joint flat Lambda CDM CMB lensing and 3x2 pt analysis is found to yield tight constraints on Omega (m) = 0.307(-0.013)(+0.008) Omega m = 0 . 307 - 0.013 + 0.008 , sigma (8) = 0.769(-0.010)(+0.022) sigma 8 = 0 . 769 - 0.010 + 0.022 , and S-8 = 0.779(-0.013)(+0.013) S 8 = 0 . 779 - 0.013 + 0.013 .

Automated summary

The study presents constraints on extensions to the standard cosmological model involving parameters related to the curvature of space, neutrino masses, and dark energy. By combining measurements from various sources, the results confirm the consistency of the flat Lambda CDM model and offer tight constraints on key parameters.