KiDS-450 : testing extensions to the standard cosmological model

We test extensions to the standard cosmological model with weak gravitational lensing tomography using 450 deg(2) of imaging data from the Kilo Degree Survey (KiDS). In these extended cosmologies, which include massive neutrinos, non-zero curvature, evolving dark energy, modified gravity and running of the scalar spectral index, we also examine the discordance between KiDS and cosmic microwave background (CMB) measurements from Planck. The discordance between the two data sets is largely unaffected by a more conservative treatment of the lensing systematics and the removal of angular scales most sensitive to non-linear physics. The only extended cosmology that simultaneously alleviates the discordance with Planck and is at least moderately favoured by the data includes evolving dark energy with a time-dependent equation of state (in the form of the w(0) - w(a) parametrization). In this model, the respective S-8 = sigma(8) root Omega(m)/0.3 constraints agree at the 1 sigma level, and there is 'substantial concordance' between the KiDS and Planck data sets when accounting for the full parameter space. Moreover, the Planck constraint on the Hubble constant is wider than in Lambda cold dark matter (Lambda CDM) and in agreement with the Riess et al. (2016) direct measurement of H-0. The dark energy model is moderately favoured as compared to Lambda CDM when combining the KiDS and Planck measurements, and marginalized constraints in the w(0)-w(a) plane are discrepant with a cosmological constant at the 3 sigma level. KiDS further constrains the sum of neutrino masses to 4.0 eV (95% CL), finds no preference for time or scale-dependent modifications to the metric potentials, and is consistent with flatness and no running of the spectral index.