KiDS-1000 Cosmology: Multi-probe weak gravitational lensing and
  spectroscopic galaxy clustering constraints
  We present a joint cosmological analysis of weak gravitational lensing
observations from the Kilo-Degree Survey (KiDS-1000), with redshift-space
galaxy clustering observations from the Baryon Oscillation Spectroscopic Survey
(BOSS), and galaxy-galaxy lensing observations from the overlap between
KiDS-1000, BOSS and the spectroscopic 2-degree Field Lensing Survey (2dFLenS).
This combination of large-scale structure probes breaks the degeneracies
between cosmological parameters for individual observables, resulting in a
constraint on the structure growth parameter $S_8=\sigma_8 \sqrt{\Omega_{\rm
m}/0.3} = 0.766^{+0.020}_{-0.014}$, that has the same overall precision as that
reported by the full-sky cosmic microwave background observations from Planck.
The recovered $S_8$ amplitude is low, however, by $8.3 \pm 2.6$ % relative to
Planck. This result builds from a series of KiDS-1000 analyses where we
validate our methodology with variable depth mock galaxy surveys, our lensing
calibration with image simulations and null-tests, and our
optical-to-near-infrared redshift calibration with multi-band mock catalogues
and a spectroscopic-photometric clustering analysis. The systematic
uncertainties identified by these analyses are folded through as nuisance
parameters in our cosmological analysis. Inspecting the offset between the
marginalised posterior distributions, we find that the $S_8$-difference with
Planck is driven by a tension in the matter fluctuation amplitude parameter,
$\sigma_8$. We quantify the level of agreement between the CMB and our
large-scale structure constraints using a series of different metrics, finding
differences with a significance ranging between $\sim\! 3\,\sigma$, when
considering the offset in $S_{8}$, and $\sim\! 2\,\sigma$, when considering the
full multi-dimensional parameter space.
