Cosmological parameter constraints for Horndeski scalar-tensor gravity
  We present new cosmological parameter constraints for general Horndeski
scalar-tensor theories, using CMB, redshift space distortion, matter power
spectrum and BAO measurements from the Planck, SDSS/BOSS and 6dF surveys. We
focus on theories with cosmological gravitational waves propagating at the
speed of light, $c_{\rm GW} = c$, implementing and discussing several
previously unaccounted for aspects in the constraint derivation for such
theories, that qualitatively affect the resulting constraints. In order to
ensure our conclusions are robust, we compare results for three different
parametrisations of the free functions in Horndeski scalar-tensor theories,
identifying several parametrisation-independent features of the constraints. We
also consider models, where $c_{\rm GW} \neq c$ in cosmological settings (still
allowed after GW170817 for frequency-dependent $c_{\rm GW}$) and show how this
affects cosmological parameter constraints.
